Management Measures Tool for Marine Renewable Energy

Accessing Management Measures that support Deployment of Wave and Tidal Devices

As the MRE industry moves beyond deployment of individual wave and tidal devices towards arrays, there continue to be onerous monitoring requirements placed on device developers. Certain risks of MRE devices on the marine environment are not sufficiently well resolved to allow smooth transitions towards a commercial industry. As an example, the potential collision of marine animals with single tidal turbines continues to create concern for stakeholders and regulators in many jurisdictions.

In consultation with the research and regulatory communities, it was determined that having a set of robust management measures might act as safeguards for marine animals and habitats until such time as definitive monitoring data become available to determine the level of risk from turbines and WECs. At that point, mitigation measures could be dialed back or removed, if warranted.

With the input of the researchers, regulators, and developers at a workshop held May 9th 2017 in Glasgow UK, the following criteria were used to develop the management measures tool shown here:

Ensure common understanding of parameters that describe management measures proposed for collision risk, EMF, noise, and benthic disturbance;
Evaluate each measure for effectiveness in addressing the risk for which it is intended;
Determine the feasibility and practicality of each measure;
Facilitate the development of a toolbox of management measures that can be made broadly available, as they are needed; and
Consider the use of the tool to guide initial discussions between project proponents and regulators.

The tool can be explored using the following steps:

Filter by Technology:

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Filter by Project Phase:

Filter by Stressor:

Filter by Receptor:

Technology	Management Measure Category	Phase of Project	Stressor	Receptor	Specific Receptor	Interaction	Specific Management Measures	Implications of Measure
Tidal	Mitigation	Operation & Maintenance	Vessel disturbance	Birds	Shore-nesting birds	Potential for disturbance from project vessels.	Avoidance of sensitive shore nesting areas during sensitive periods with appropriate clearance distance.	Reduces potential effects and is a relatively low cost measure.
Wave	None identified	Operation & Maintenance	Barrier to movement	Fish	Basking shark; Whale shark; Fish	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Tidal	Mitigation	Installation	Changes in sediment dynamics	Fish	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Decommissioning	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Operation & Maintenance	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. Alrhough, use of lower toxicity materials may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Compliance	Installation	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Migratory fish; Elasmobranchs	Impacts of electromagnetic fields from subsea cables on sensitive species.	Install cable protection/ armour/ rock placement/ other cable protection.	Reduces the level of EMF to surrounding water column and therefore any potential effects. Reduces 'snagging risk' for vessels and may create habitat for species. Potential for adverse impacts on surrounding benthic habitats and sensitive species, e.g. from smothering. This measure forms part of normal project design.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Elasmobranchs	Impacts of electromagnetic fields from subsea cables on sensitive species.	Bundle cables together to reduce field vectors.	Reduce the level of EMF to surrounding water column and therefore any potential effects. Could result in there being less redundancy in the system and potential commercial and technical feasibility issues.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Limit cable voltage.	n/a
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Strategic use of rock placement/other cable protection.	n/a
Wave	Design feature	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in device mooring lines and cables.	Cable design with maximum bend radius.	Would remove/reduce risk of entanglement, however cable design driven by technical and commercial consideration. Entanglement records are a useful way to track events.
Wave	Monitoring	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in lost fishing gear or other equipment trapped on infrastructure.	Ensure standard notifications of loss of fishing gear in region notified to operators. Reporting of entanglement events.	Good practice for emergency preparedness.
Wave	Monitoring	Operation & Maintenance	Habitat creation	Fish	All receptors	The introduction of infrastructure and artificial substrates will provide habitat and artificial refuges.	Monitor near-field behaviours.	Informs understanding of potential positive impacts from colonisation and use of the project infrastructure which could benefit future project applications. However, there is a cost implication associated with monitoring.
Wave	Design feature	Installation	Loss of habitat	Fish	Demersal fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Minimise footprint of anchors / foundations.	This could reduce effects on sensitive habitats, however may impact technical considerations.
Wave	Mitigation	Installation	Loss of seabed habitat	Fish	Fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Use of locally sourced materials, for cable protection, of the same type as the habitat to be disturbed by cable installation.	Minimise impact on biodiversity/ ecosystem.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Wave	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Installation	Underwater noise	Fish	Fish	The potential effects from underwater noise generated during installation/ construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Wave	Mitigation	Decommissioning	Vessel disturbance	Fish	Large fish	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Installation	Airborne noise	Marine Mammals	Marine Mammals	The potential effects from airborne noise generated during installation/construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs and important cliff nesting sites, during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, however may could increase project construction timescales e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Tidal	Mitigation	Installation	Changes in sediment dynamics	Marine Mammals	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Monitoring	Operation & Maintenance	Collision risk	Marine Mammals	Marine Mammals	Potential for collision with turbine blades.	Install a 'detect and shut-down' system using active sonar and other appropriate monitoring equipment.	This could reduce/remove risk of collision with moving blades and enable a route through the consenting process, particulalrly at high sensitivity locations. However, this could affect power production, is expensive to implement and does not help to reduce scientific uncertainty regarding the risk. The reductions in power production, although small, would bring about uncertainty in the investment process and there are questions around impacts of sonar on sensitive species.
Tidal	Monitoring	Operation & Maintenance	Collision risk	Marine Mammals	Marine Mammals	Potential for collision with turbine blades.	Environmental monitoring to better understand near-field behaviour and avoidance.	This will help reduce scientific uncertainty, however monitoring can be costly.
Wave	Mitigation	Installation	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Decommissioning	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Mitigation	Operation & Maintenance	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event, ensures that contingency plans are in place and demonstrates compliance with environmental management systems.
Wave	None identified	Operation & Maintenance	Displacement	Marine Mammals	Marine Mammals	Potential displacement of essential activities due to the presence of devices and associated moorings / support structures.	None identified.	n/a
Wave	Monitoring	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Install tension sensors on mooring lines.	Informs of problem with mooring lines allowing rectification, however this comes at an additional cost and control system integration requirement.
Wave	Monitoring	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Removes/reduces risk of entanglement and is a low cost monitoring capability.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Monitoring	Decommissioning	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Wave	Monitoring	Operation & Maintenance	Underwater noise	Marine Mammals	Marine Mammals	The potential effects from underwater noise generated by wave and tidal energy converters.	Measure noise generated by device(s) during operation to better understand the potential effects on sensitive species.	Measured noise levels can be correlated with threshold values of relevant species to determine impact and need for adaptive management measures, however this can be complex and costly to undertake this type of monitoring in high energy environments.
Wave	Mitigation	Installation	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Installation	Vessel disturbance	Marine Mammals	Seals	Disturbance at seal haul-out sites from project vessels.	Avoid transiting within 500m of known seal haul outs.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Decommissioning	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Care will be taken to avoid splitting up groups and mothers and young.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Installation	Changes in sediment dynamics	Reptiles	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Decommissioning	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Operation & Maintenance	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. Although, use of lower toxicity materials may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Installation	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Compliance	Decommissioning	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Monitoring	Operation & Maintenance	Entanglement	Reptiles	Sea turtles	Potential for marine animals to become entangled in lost fishing gear or other equipment trapped on infrastructure.	Ensure standard notifications of loss of fishing gear in region notified to operators. Reporting of entanglement events.	Good practice for emergency preparedness.
Wave	Mitigation	Operation & Maintenance	Entrapment	Reptiles	All receptors	Potential risk of entrapment within device chambers and mooring arrays.	Release entrapped animal.	n/a
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	None identified	Operation & Maintenance	Barrier to movement	Habitat	All receptors	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Tidal	Mitigation	Installation	Changes in sediment dynamics	Habitat	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Operation & Maintenance	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Installation	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, the use of lower toxicity materials may compromise performance, or impact other technical issue (e.g. fluuid changes).
Tidal	Mitigation	Decommissioning	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Compliance	Operation & Maintenance	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Installation	Loss of habitat	Habitat	Intertidal ecology	Direct loss of protected or sensitive intertidal communities from changes in hydrodynamics due to nearshore WECs.	Micrositing of nearshore WECs to minimise the impact on sensitive habitats and species.	n/a
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Design feature	Installation	Changes in sediment dynamics	Benthic	Fish, Benthic invertebrates	The potential wider or secondary effects (siltation changes or smothering) on protected or sensitive sub-littoral seabed due to scour or siltation around devices and associated moorings, support structures and export cables.	Micrositing of export cables and infrastructure to minimize the impact on sensitive habitats and species. Best practice techniques for cable installation, burial and protection.	Reduces, limits or offsets potential impacts on sensitive habitats and species.
Tidal	Mitigation	Installation	Changes in sediment dynamics	Benthic	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Design feature	Decommissioning	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Operation & Maintenance	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Compliance	Installation	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organization (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from subsea cables on sensitive species.	Use of 3-phase cables instead of DC cables.	Reduces the level of EMF to surrounding water column and therefore any potential effects, however there are potential commercial and technical feasibility issues surrounding the specific project requirements as well as some disagreement as to the efficacy of this measure.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from subsea cables on sensitive species.	Bury or HDD cables where possible and viable.	Reduces the level of EMF to surrounding water column and therefore any potential effects, however the implementation of this measure may have an impact on surrounding benthic habitats and sensitive species. Also reduces 'snagging risk' for vessels. This measure forms part of normal project design.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Strategic use of rock placement/other cable protection	n/a
Wave	Monitoring	Operation & Maintenance	Habitat creation	Benthic	All receptors	The introduction of infrastructure and artificial substrates will provide habitat and artificial refuges.	Monitor near-field behaviors .	Informs understanding of potential positive impacts from colonization and use of the project infrastructure which could benefit future project applications, however there is a cost implication associated with monitoring.
Tidal	Design feature	Installation	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Minimize footprint of anchors / foundations.	This could reduce effects on sensitive habitats, however the size of anchors/foundations likely to be that which is suitable for the safe and optimal operation of devices.
Tidal	Mitigation	Installation	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Use of locally sourced materials, for cable protection, of the same type as the habitat to be disturbed by cable installation.	Minimize impact on biodiversity/ ecosystem.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Monitoring	Operation & Maintenance	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Installation	Airborne noise	Birds	Seabirds	The potential effects from airborne noise generated during installation/construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs and important cliff nesting sites, during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Tidal	Mitigation	Installation	Changes in sediment dynamics	Birds	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Monitoring	Operation & Maintenance	Collision risk	Birds	Diving birds	Potential for collision with turbine blades.	Environmental monitoring to better understand near-field behaviour and avoidance.	Would reduce scientific uncertainty around the issue, however can be costly to implement.
Wave	Mitigation	Installation	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Decommissioning	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Mitigation	Operation & Maintenance	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	None identified	Operation & Maintenance	Displacement	Birds	Seabirds	Potential displacement of essential activities due to the presence of devices and associated moorings / support structures.	None identified.	n/a
Wave	Monitoring	Operation & Maintenance	Entanglement	Birds	Diving birds	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Would remove/reduce risk of entanglement and is a low cost monitoring capability.
Wave	Monitoring	Operation & Maintenance	Habitat creation	Birds	Roosting birds	The introduction of infrastructure and artificial substrates will provide potential roosting habitat.	Monitor use of device as a roosting platform.	Reduces scientific uncertainty around collision risk, displacement and other impacts, however this type of monitoring can be expensive.
Wave	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Would remove/reduce risk of transfer and settlement of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Wave	Monitoring	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Installation	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Do not break up or 'flush' rafts of birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Also pertinent to note that the measure is selectively applied to project vessels in context of other vessel operations.
Wave	Mitigation	Decommissioning	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Adhere to minimum approach distances for vessels on approach to marine mammals and birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Can increase the time of operational procedures and thus increase cost. Further monitoring, e.g. defining of approach distances and then comparing these to see which are most effective would validate the efficacy of the measure.
Tidal	Mitigation	Decommissioning	Vessel disturbance	Birds	Shore-nesting birds	Potential for disturbance from project vessels.	Avoidance of sensitive shore nesting areas during sensitive periods with appropriate clearance distance.	Reduces potential effects and is a relatively low cost measure.
Tidal	None identified	Operation & Maintenance	Barrier to movement	Fish	Basking shark; Whale shark; Fish	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Tidal	Mitigation	Decommissioning	Changes in sediment dynamics	Fish	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Design feature	Installation	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Decommissioning	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. Alrhough, use of lower toxicity materials may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Compliance	Operation & Maintenance	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Migratory fish; Elasmobranchs	Impacts of electromagnetic fields from subsea cables on sensitive species.	Install cable protection/ armour/ rock placement/ other cable protection.	Reduces the level of EMF to surrounding water column and therefore any potential effects. Reduces 'snagging risk' for vessels and may create habitat for species. Potential for adverse impacts on surrounding benthic habitats and sensitive species, e.g. from smothering. This measure forms part of normal project design.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Elasmobranchs	Impacts of electromagnetic fields from subsea cables on sensitive species.	Bundle cables together to reduce field vectors.	Reduce the level of EMF to surrounding water column and therefore any potential effects. Could result in there being less redundancy in the system and potential commercial and technical feasibility issues.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Limit cable voltage.	n/a
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Strategic use of rock placement/other cable protection.	n/a
Tidal	Design feature	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in device mooring lines and cables.	Cable design with maximum bend radius.	Would remove/reduce risk of entanglement, however cable design driven by technical and commercial consideration. Entanglement records are a useful way to track events.
Tidal	Monitoring	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in lost fishing gear or other equipment trapped on infrastructure.	Ensure standard notifications of loss of fishing gear in region notified to operators. Reporting of entanglement events.	Good practice for emergency preparedness.
Tidal	Monitoring	Operation & Maintenance	Habitat creation	Fish	All receptors	The introduction of infrastructure and artificial substrates will provide habitat and artificial refuges.	Monitor near-field behaviours.	Informs understanding of potential positive impacts from colonisation and use of the project infrastructure which could benefit future project applications. However, there is a cost implication associated with monitoring.
Wave	Design feature	Decommissioning	Loss of habitat	Fish	Demersal fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Minimise footprint of anchors / foundations.	This could reduce effects on sensitive habitats, however may impact technical considerations.
Wave	Mitigation	Decommissioning	Loss of seabed habitat	Fish	Fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Use of locally sourced materials, for cable protection, of the same type as the habitat to be disturbed by cable installation.	Minimise impact on biodiversity/ ecosystem.
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Tidal	Compliance	Installation	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Tidal	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Underwater noise	Fish	Fish	The potential effects from underwater noise generated during installation/ construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Tidal	Mitigation	Installation	Vessel disturbance	Fish	Large fish	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Decommissioning	Airborne noise	Marine Mammals	Marine Mammals	The potential effects from airborne noise generated during installation/construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs and important cliff nesting sites, during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, however may could increase project construction timescales e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Tidal	Mitigation	Decommissioning	Changes in sediment dynamics	Marine Mammals	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Design feature	Operation & Maintenance	Collision risk	Marine Mammals	Marine Mammals	Potential for collision with turbine blades.	Install a 'detect and shut-down' system using active sonar and other appropriate monitoring equipment.	This could reduce/remove risk of collision with moving blades and enable a route through the consenting process, particulalrly at high sensitivity locations. However, this could affect power production, is expensive to implement and does not help to reduce scientific uncertainty regarding the risk. The reductions in power production, although small, would bring about uncertainty in the investment process and there are questions around impacts of sonar on sensitive species.
Tidal	Mitigation	Operation & Maintenance	Collision risk	Marine Mammals	Marine Mammals	Potential for collision with turbine blades.	Selective structural and blade coatings i.e. colours to aide detection.	Unknown - it is possible that this will aid detection of subsea structures and help reduce risk. It can be captured in early project design for a small one-off cost, however further research is needed as there is potential for an increased collision risk through 'attraction'.
Wave	Mitigation	Operation & Maintenance	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Installation	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Mitigation	Decommissioning	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event, ensures that contingency plans are in place and demonstrates compliance with environmental management systems.
Tidal	None identified	Operation & Maintenance	Displacement	Marine Mammals	Marine Mammals	Potential displacement of essential activities due to the presence of devices and associated moorings / support structures.	None identified.	n/a
Tidal	Monitoring	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Install tension sensors on mooring lines.	Informs of problem with mooring lines allowing rectification, however this comes at an additional cost and control system integration requirement.
Tidal	Monitoring	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Removes/reduces risk of entanglement and is a low cost monitoring capability.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Installation	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Monitoring	Installation	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Tidal	Monitoring	Operation & Maintenance	Underwater noise	Marine Mammals	Marine Mammals	The potential effects from underwater noise generated by wave and tidal energy converters.	Measure noise generated by device(s) during operation to better understand the potential effects on sensitive species.	Measured noise levels can be correlated with threshold values of relevant species to determine impact and need for adaptive management measures, however this can be complex and costly to undertake this type of monitoring in high energy environments.
Wave	Mitigation	Operation & Maintenance	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Operation & Maintenance	Vessel disturbance	Marine Mammals	Seals	Disturbance at seal haul-out sites from project vessels.	Avoid transiting within 500m of known seal haul outs.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Installation	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Care will be taken to avoid splitting up groups and mothers and young.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Decommissioning	Changes in sediment dynamics	Reptiles	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Design feature	Installation	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Decommissioning	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. Although, use of lower toxicity materials may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Operation & Maintenance	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Compliance	Installation	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Monitoring	Operation & Maintenance	Entanglement	Reptiles	Sea turtles	Potential for marine animals to become entangled in lost fishing gear or other equipment trapped on infrastructure.	Ensure standard notifications of loss of fishing gear in region notified to operators. Reporting of entanglement events.	Good practice for emergency preparedness.
Tidal	Mitigation	Operation & Maintenance	Entrapment	Reptiles	All receptors	Potential risk of entrapment within device chambers and mooring arrays.	Release entrapped animal.	n/a
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Compliance	Installation	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	None identified	Operation & Maintenance	Barrier to movement	Habitat	All receptors	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Tidal	Mitigation	Decommissioning	Changes in sediment dynamics	Habitat	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Decommissioning	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Operation & Maintenance	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, the use of lower toxicity materials may compromise performance, or impact other technical issue (e.g. fluuid changes).
Wave	Mitigation	Installation	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Compliance	Decommissioning	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	Loss of habitat	Habitat	Intertidal ecology	Direct loss of protected or sensitive intertidal communities from changes in hydrodynamics due to nearshore WECs.	Micrositing of nearshore WECs to minimise the impact on sensitive habitats and species.	n/a
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Compliance	Installation	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Design feature	Operation & Maintenance	Changes in sediment dynamics	Benthic	Fish, Benthic invertebrates	The potential wider or secondary effects (siltation changes or smothering) on protected or sensitive sub-littoral seabed due to scour or siltation around devices and associated moorings, support structures and export cables.	Micrositing of export cables and infrastructure to minimize the impact on sensitive habitats and species. Best practice techniques for cable installation, burial and protection.	Reduces, limits or offsets potential impacts on sensitive habitats and species.
Tidal	Mitigation	Decommissioning	Changes in sediment dynamics	Benthic	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Mitigation	Installation	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Decommissioning	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Compliance	Operation & Maintenance	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organization (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from subsea cables on sensitive species.	Use of 3-phase cables instead of DC cables.	Reduces the level of EMF to surrounding water column and therefore any potential effects, however there are potential commercial and technical feasibility issues surrounding the specific project requirements as well as some disagreement as to the efficacy of this measure.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from subsea cables on sensitive species.	Bury or HDD cables where possible and viable.	Reduces the level of EMF to surrounding water column and therefore any potential effects, however the implementation of this measure may have an impact on surrounding benthic habitats and sensitive species. Also reduces 'snagging risk' for vessels. This measure forms part of normal project design.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Strategic use of rock placement/other cable protection	n/a
Tidal	Monitoring	Operation & Maintenance	Habitat creation	Benthic	All receptors	The introduction of infrastructure and artificial substrates will provide habitat and artificial refuges.	Monitor near-field behaviors .	Informs understanding of potential positive impacts from colonization and use of the project infrastructure which could benefit future project applications, however there is a cost implication associated with monitoring.
Tidal	Design feature	Decommissioning	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Minimize footprint of anchors / foundations.	This could reduce effects on sensitive habitats, however the size of anchors/foundations likely to be that which is suitable for the safe and optimal operation of devices.
Tidal	Mitigation	Decommissioning	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Use of locally sourced materials, for cable protection, of the same type as the habitat to be disturbed by cable installation.	Minimize impact on biodiversity/ ecosystem.
Wave	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Monitoring	Decommissioning	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Airborne noise	Birds	Seabirds	The potential effects from airborne noise generated during installation/construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs and important cliff nesting sites, during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Tidal	Mitigation	Decommissioning	Changes in sediment dynamics	Birds	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Mitigation	Operation & Maintenance	Collision risk	Birds	Diving birds	Potential for collision with turbine blades.	Selective structural and blade coatings i.e. colours to aide detection.	Unknown - it is possible that this will aid detection of subsea structures and help reduce risk at a low cost. Lack of understanding and further research needed, it may be that certain colours could result in attraction resulting in an increase in collision risk.
Wave	Mitigation	Operation & Maintenance	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Installation	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Mitigation	Decommissioning	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	None identified	Operation & Maintenance	Displacement	Birds	Seabirds	Potential displacement of essential activities due to the presence of devices and associated moorings / support structures.	None identified.	n/a
Tidal	Monitoring	Operation & Maintenance	Entanglement	Birds	Diving birds	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Would remove/reduce risk of entanglement and is a low cost monitoring capability.
Tidal	Monitoring	Operation & Maintenance	Habitat creation	Birds	Roosting birds	The introduction of infrastructure and artificial substrates will provide potential roosting habitat.	Monitor use of device as a roosting platform.	Reduces scientific uncertainty around collision risk, displacement and other impacts, however this type of monitoring can be expensive.
Tidal	Compliance	Installation	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Would remove/reduce risk of transfer and settlement of non-native species.
Tidal	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Installation	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Tidal	Monitoring	Installation	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Operation & Maintenance	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Do not break up or 'flush' rafts of birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Also pertinent to note that the measure is selectively applied to project vessels in context of other vessel operations.
Tidal	Mitigation	Installation	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Adhere to minimum approach distances for vessels on approach to marine mammals and birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Can increase the time of operational procedures and thus increase cost. Further monitoring, e.g. defining of approach distances and then comparing these to see which are most effective would validate the efficacy of the measure.
Wave	Mitigation	Installation	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Vessel transit route: defining routes to avoid sensitive sites and to only disturb one route.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Installation	Changes in sediment dynamics	Fish	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Monitoring	Operation & Maintenance	Collision risk	Fish	Fish	Potential for collision with turbine blades.	Environmental monitoring to detect collision events.	Helps to develop an understanding of avoidance behaviour, nature of interactions and outcome of collision events. However, there are cost implications assocaited with this level of monitoring.
Tidal	Design feature	Operation & Maintenance	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Installation	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Compliance	Decommissioning	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Migratory fish	Impacts of electromagnetic fields from subsea cables on sensitive species.	Use of 3-phase cables instead of DC cables.	Reduce the level of EMF to surrounding water column and therefore any potential effects. Potential commercial and technical feasibility issues some disagreement as to efficacy of this measure. Additionally, the cables used will largely depend upon the project requirements.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Migratory fish	Impacts of electromagnetic fields from subsea cables on sensitive species.	Bury or HDD cables where possible and viable.	Reduces the level of EMF to surrounding water column and therefore any potential effects. Reduces 'snagging risk' for vessels. Potential for adverse impacts on surrounding benthic habitats and sensitive species, e.g. from smothering. This measure forms part of normal project design.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Use of 3-phase cables instead of DC cables.	n/a
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Bundle cables together to reduce field vectors.	n/a
Wave	Design feature	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in device mooring lines and cables.	Install tension sensors on mooring lines.	Informs of problem with mooring lines allowing rectification, however their implementation would come at an additional cost and would require control system integration.
Wave	Design feature	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Would remove/reduce risk of entanglement and is a low cost monitoring capability.
Wave	Design feature	Operation & Maintenance	Lighting	Fish	Fish	Potential for lighting to adversely affect nocturnal and migratory species.	Consider type, colour and use of lighting during design and consultation with navigational stakeholders.	A targeted lighting plan may have the potential to reduce impacts on sensitive species but navigational safety takes precedence.
Tidal	Design feature	Installation	Loss of habitat	Fish	Demersal fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Minimise footprint of anchors / foundations.	This could reduce effects on sensitive habitats, however may impact technical considerations.
Tidal	Mitigation	Installation	Loss of seabed habitat	Fish	Fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Use of locally sourced materials, for cable protection, of the same type as the habitat to be disturbed by cable installation.	Minimise impact on biodiversity/ ecosystem.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Wave	Monitoring	Installation	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Tidal	Mitigation	Installation	Underwater noise	Fish	Fish	The potential effects from underwater noise generated during installation/ construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Tidal	Mitigation	Operation & Maintenance	Vessel disturbance	Fish	Large fish	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Wave	None identified	Operation & Maintenance	Barrier to movement	Marine Mammals	Seals; Cetaceans	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Wave	Mitigation	Installation	Changes in sediment dynamics	Marine Mammals	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Mitigation	Operation & Maintenance	Collision risk	Marine Mammals	Marine Mammals	Potential for collision with turbine blades.	Install a 'detect and deter' system using a combination of active sonar and acoustic deterrent device (ADD).	This could reduce likelihood of collision with moving blades although the efficacy of ADDs in these environments is unknown and habituation to ADDs is known to occur in other industries. Could enable a route through the consenting process. This measure is expensive to implement and it is still unknown if deterrent systems will help reduce risk. There are also questions around the effects of ADDs on sensitive species. Their addition adds another noise impact which must also be considered in any project assessments. Would rely on well proven and reliable 'detect and deter' systems. Also, mitigation against collision may prevent discovering whether or not it is a real issue. Further research around ADDs which deter specific groups or species, is underway. This could be useful in deterring specific sensitive species or species groups, at a particular site. For example, University of St Andrews is seveloping an ADD which deter seals, but which don't effect cetaceans.
Wave	Design feature	Installation	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Decommissioning	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Operation & Maintenance	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Compliance	Installation	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event, ensures that contingency plans are in place and demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Maintain taut mooring lines.	Removes/reduces risk of entanglement, however mooring design tends to be driven by technical and commercial consideration. An entanglement record is a useful way to track events.
Wave	Monitoring	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Fishing debris detected during routine inspections of mooring lines and cables will be removed.	Removes/reduces risk of entanglement and is a low cost measure, implemented as part of standard O&M procedures.
Wave	Mitigation	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in lost fishing gear or other equipment trapped on infrastructure.	Fisheries management: Agreement with fishermen not to fish near to the device, warning of the dangers of losing equipment.	Reduces potential for entanglement of fishing gear in mooring lines and thus potential for entanglement of marine animals.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Monitoring	Operation & Maintenance	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Wave	Mitigation	Installation	Vessel collision	Marine Mammals	Cetaceans	Potential for collision with project vessels.	Adhere to minimum approach distances for vessels on approach.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Decommissioning	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Decommissioning	Vessel disturbance	Marine Mammals	Seals	Disturbance at seal haul-out sites from project vessels.	Avoid transiting within 500m of known seal haul outs.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Operation & Maintenance	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Care will be taken to avoid splitting up groups and mothers and young.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Installation	Changes in sediment dynamics	Reptiles	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Design feature	Operation & Maintenance	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Installation	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Mitigation	Decommissioning	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Compliance	Operation & Maintenance	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	Entanglement	Reptiles	Sea turtles	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Removes/reduces risk of entanglement and is a low cost monitoring capability.
Wave	Monitoring	Operation & Maintenance	Habitat creation	Reptiles	All receptors	The introduction of infrastructure and artificial substrates will provide habitat and artificial refuges.	Monitor near-field behaviours.	Informs understanding of potential positive impacts from colonisation and use of the project infrastructure which could benefit future project applications. However, there is a cost implication associated with monitoring.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Monitoring	Installation	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Wave	Mitigation	Installation	Changes in sediment dynamics	Habitat	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Monitoring	Operation & Maintenance	Changes in sediment dynamics	Habitat	Benthic species	The potential wider or secondary effects (siltation changes or smothering) on protected or sensitive littoral habitat due to devices and associated moorings, support structures or landfall cables.	Periodic visual monitoring through the use of divers, drop down video or intertidal shore surveys.	n/a
Tidal	Design feature	Installation	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Decommissioning	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, the use of lower toxicity materials may compromise performance, or impact other technical issue (e.g. fluuid changes).
Wave	Mitigation	Operation & Maintenance	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Compliance	Installation	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Installation	Loss of habitat	Habitat	Intertidal ecology	Loss of intertidal habitat from trenching for cable landfall.	Pre-construction cable route surveys to avoid sensitive habitats.	n/a
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Installation	Changes in sediment dynamics	Benthic	All receptors	Reduced visibility from altered water clarity associated with sediment mixing that can impact prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Monitoring	Operation & Maintenance	Changes in water flow	Benthic	Benthic invertebrates	The potential wider or secondary effects on protected or sensitive sub-littoral seabed due to removal or alteration of tidal flow arising from devices and moorings or support structures.	Pre and post installation monitoring of sensitive benthic communities, based on diver, drop down, static visual surveys (camera) or grab sampling.	Would result in a reduction of scientific uncertainty, however interpretation of data for statistical purposes may not have power to detect change generated by impact. In addition it may require correlation with detailed Computational Fluid Dynamics studies and physical flow measurements.
Wave	Mitigation	Operation & Maintenance	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Installation	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Compliance	Decommissioning	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organization (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Limit cable voltage	n/a
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Lay cables in natural crevices	n/a
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Bundle cables together to reduce field vectors	n/a
Wave	Design feature	Installation	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Micrositing of offshore infrastructure to avoid sensitive habitats.	This could reduce/remove effects on sensitive habitats and can often be done with little additional costs.
Wave	Design feature	Installation	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Cable protection management measures to ensure that any rock placement that is required will be kept to a minimum to reduce seabed disturbance.	This could reduce effects on sensitive habitats.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Wave	Design feature	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Avoid the introduction of hard bottom substrate into a soft bottom habitat.	Ensures the efficient recovery of species native to the surrounding habitat. May have technical implications.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Tidal	Mitigation	Installation	Airborne noise	Birds	Seabirds	The potential effects from airborne noise generated during installation/construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs and important cliff nesting sites, during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Wave	Mitigation	Installation	Changes in sediment dynamics	Birds	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Installation	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Decommissioning	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Operation & Maintenance	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Compliance	Installation	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	Entanglement	Birds	Diving birds	Potential for marine animals to become entangled in device mooring lines and cables.	Maintain taut mooring lines.	Would remove/reduce risk of entanglement, however mooring design driven by technical and commercial consideration. Entanglement records are a useful way to track events.
Wave	Design feature	Operation & Maintenance	Entanglement	Birds	Diving birds	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Would remove/reduce risk of entanglement and is a low cost monitoring capability.
Wave	Design feature	Operation & Maintenance	Lighting	Birds	Seabirds	Potential for lighting to adversely affect nocturnal and migratory species.	Consider type, colour and use of lighting during design and consultation with navigational stakeholders.	A targeted lighting plan may have the potential to reduce impacts on sensitive species but navigational safety takes precedence.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Would remove/reduce risk of transfer and settlement of non-native species.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Tidal	Monitoring	Operation & Maintenance	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Do not break up or 'flush' rafts of birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Also pertinent to note that the measure is selectively applied to project vessels in context of other vessel operations.
Tidal	Mitigation	Operation & Maintenance	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Adhere to minimum approach distances for vessels on approach to marine mammals and birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Can increase the time of operational procedures and thus increase cost. Further monitoring, e.g. defining of approach distances and then comparing these to see which are most effective would validate the efficacy of the measure.
Wave	Mitigation	Operation & Maintenance	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Vessel transit route: defining routes to avoid sensitive sites and to only disturb one route.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Decommissioning	Changes in sediment dynamics	Fish	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Mitigation	Operation & Maintenance	Collision risk	Fish	Fish	Potential for collision with turbine blades.	Implement a 'soft start'/cut in speed management approach at sensitive sites, i.e. those where the potential for collisions is high.	Soft start - this could reduce risk by allowing marine mammals time to move away from the turbine and could be done at a relatively low cost. Cut in speed management - this could be used to reduce risk during periods of known higher activity in sensitive sites. It is still unclear whether these offer additional mitigation and to an extent a soft start happens naturally. Implementation of this measure could result in a loss of revenue for the developer.
Tidal	Design feature	Decommissioning	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Operation & Maintenance	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Compliance	Installation	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Migratory fish	Impacts of electromagnetic fields from subsea cables on sensitive species.	Use of 3-phase cables instead of DC cables.	Reduce the level of EMF to surrounding water column and therefore any potential effects. Potential commercial and technical feasibility issues some disagreement as to efficacy of this measure. Additionally, the cables used will largely depend upon the project requirements.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Migratory fish	Impacts of electromagnetic fields from subsea cables on sensitive species.	Bury or HDD cables where possible and viable.	Reduces the level of EMF to surrounding water column and therefore any potential effects. Reduces 'snagging risk' for vessels. Potential for adverse impacts on surrounding benthic habitats and sensitive species, e.g. from smothering. This measure forms part of normal project design.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Use of 3-phase cables instead of DC cables.	n/a
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Bundle cables together to reduce field vectors.	n/a
Tidal	Design feature	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in device mooring lines and cables.	Install tension sensors on mooring lines.	Informs of problem with mooring lines allowing rectification, however their implementation would come at an additional cost and would require control system integration.
Tidal	Design feature	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Would remove/reduce risk of entanglement and is a low cost monitoring capability.
Tidal	Design feature	Operation & Maintenance	Lighting	Fish	Fish	Potential for lighting to adversely affect nocturnal and migratory species.	Consider type, colour and use of lighting during design and consultation with navigational stakeholders.	A targeted lighting plan may have the potential to reduce impacts on sensitive species but navigational safety takes precedence.
Tidal	Design feature	Decommissioning	Loss of habitat	Fish	Demersal fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Minimise footprint of anchors / foundations.	This could reduce effects on sensitive habitats, however may impact technical considerations.
Tidal	Mitigation	Decommissioning	Loss of seabed habitat	Fish	Fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Use of locally sourced materials, for cable protection, of the same type as the habitat to be disturbed by cable installation.	Minimise impact on biodiversity/ ecosystem.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/removes risk of transfer of non-native species.
Tidal	Mitigation	Installation	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Wave	Monitoring	Operation & Maintenance	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Tidal	Mitigation	Decommissioning	Underwater noise	Fish	Fish	The potential effects from underwater noise generated during installation/ construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Tidal	Mitigation	Decommissioning	Vessel disturbance	Fish	Large fish	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Tidal	None identified	Operation & Maintenance	Barrier to movement	Marine Mammals	Seals; Cetaceans	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Wave	Mitigation	Decommissioning	Changes in sediment dynamics	Marine Mammals	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Design feature	Operation & Maintenance	Collision risk	Marine Mammals	Marine Mammals	Potential for collision with turbine blades.	Install a 'detect and deter' system using a combination of active sonar and acoustic deterrent device (ADD).	This could reduce likelihood of collision with moving blades although the efficacy of ADDs in these environments is unknown and habituation to ADDs is known to occur in other industries. Could enable a route through the consenting process. This measure is expensive to implement and it is still unknown if deterrent systems will help reduce risk. There are also questions around the effects of ADDs on sensitive species. Their addition adds another noise impact which must also be considered in any project assessments. Would rely on well proven and reliable 'detect and deter' systems. Also, mitigation against collision may prevent discovering whether or not it is a real issue. Further research around ADDs which deter specific groups or species, is underway. This could be useful in deterring specific sensitive species or species groups, at a particular site. For example, University of St Andrews is seveloping an ADD which deter seals, but which don't effect cetaceans.
Wave	Design feature	Operation & Maintenance	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Installation	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Decommissioning	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Compliance	Operation & Maintenance	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event, ensures that contingency plans are in place and demonstrates compliance with environmental management systems.
Tidal	Design feature	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Maintain taut mooring lines.	Removes/reduces risk of entanglement, however mooring design tends to be driven by technical and commercial consideration. An entanglement record is a useful way to track events.
Tidal	Monitoring	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Fishing debris detected during routine inspections of mooring lines and cables will be removed.	Removes/reduces risk of entanglement and is a low cost measure, implemented as part of standard O&M procedures.
Tidal	Mitigation	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in lost fishing gear or other equipment trapped on infrastructure.	Fisheries management: Agreement with fishermen not to fish near to the device, warning of the dangers of losing equipment.	Reduces potential for entanglement of fishing gear in mooring lines and thus potential for entanglement of marine animals.
Tidal	Mitigation	Installation	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Installation	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Monitoring	Decommissioning	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Wave	Mitigation	Operation & Maintenance	Vessel collision	Marine Mammals	Cetaceans	Potential for collision with project vessels.	Adhere to minimum approach distances for vessels on approach.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Installation	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Installation	Vessel disturbance	Marine Mammals	Seals	Disturbance at seal haul-out sites from project vessels.	Avoid transiting within 500m of known seal haul outs.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Decommissioning	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Care will be taken to avoid splitting up groups and mothers and young.	Reduces potential effects and is a relatively low cost measure.
Wave	Mitigation	Decommissioning	Changes in sediment dynamics	Reptiles	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Design feature	Decommissioning	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Operation & Maintenance	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Mitigation	Installation	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Compliance	Decommissioning	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Design feature	Operation & Maintenance	Entanglement	Reptiles	Sea turtles	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Removes/reduces risk of entanglement and is a low cost monitoring capability.
Tidal	Monitoring	Operation & Maintenance	Habitat creation	Reptiles	All receptors	The introduction of infrastructure and artificial substrates will provide habitat and artificial refuges.	Monitor near-field behaviours.	Informs understanding of potential positive impacts from colonisation and use of the project infrastructure which could benefit future project applications. However, there is a cost implication associated with monitoring.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Mitigation	Installation	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Monitoring	Operation & Maintenance	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Changes in sediment dynamics	Habitat	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Monitoring	Operation & Maintenance	Changes in sediment dynamics	Habitat	Benthic species	The potential wider or secondary effects (siltation changes or smothering) on protected or sensitive littoral habitat due to devices and associated moorings, support structures or landfall cables.	Periodic visual monitoring through the use of divers, drop down video or intertidal shore surveys.	n/a
Tidal	Design feature	Operation & Maintenance	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Installation	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Mitigation	Decommissioning	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Compliance	Operation & Maintenance	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Design feature	Installation	Loss of habitat	Habitat	Intertidal ecology	Loss of intertidal habitat from trenching for cable landfall.	Pre-construction cable route surveys to avoid sensitive habitats.	n/a
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Mitigation	Installation	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Decommissioning	Changes in sediment dynamics	Benthic	All receptors	Reduced visibility from altered water clarity associated with sediment mixing that can impact prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Installation	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Decommissioning	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Operation & Maintenance	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Monitoring	Operation & Maintenance	Dissipation of wave energy	Benthic	Benthic invertebrates	The potential wider or secondary effects on protected or sensitive sub-littoral seabed due to removal or alteration of energy flow arising from devices and moorings or support structures.	Standard benthic and intertidal surveys focused on indicator species.	Would result in a reduction of scientific uncertainty around the interaction, however determining impacts against natural variability may be difficult.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Limit cable voltage	n/a
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Lay cables in natural crevices	n/a
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Bundle cables together to reduce field vectors	n/a
Wave	Design feature	Decommissioning	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Micrositing of offshore infrastructure to avoid sensitive habitats.	This could reduce/remove effects on sensitive habitats and can often be done with little additional costs.
Wave	Design feature	Decommissioning	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Cable protection management measures to ensure that any rock placement that is required will be kept to a minimum to reduce seabed disturbance.	This could reduce effects on sensitive habitats.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Tidal	Design feature	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Avoid the introduction of hard bottom substrate into a soft bottom habitat.	Ensures the efficient recovery of species native to the surrounding habitat. May have technical implications.
Wave	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Tidal	Mitigation	Decommissioning	Airborne noise	Birds	Seabirds	The potential effects from airborne noise generated during installation/construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs and important cliff nesting sites, during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Wave	Mitigation	Decommissioning	Changes in sediment dynamics	Birds	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Operation & Maintenance	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Installation	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Decommissioning	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Compliance	Operation & Maintenance	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Design feature	Operation & Maintenance	Entanglement	Birds	Diving birds	Potential for marine animals to become entangled in device mooring lines and cables.	Maintain taut mooring lines.	Would remove/reduce risk of entanglement, however mooring design driven by technical and commercial consideration. Entanglement records are a useful way to track events.
Tidal	Design feature	Operation & Maintenance	Entanglement	Birds	Diving birds	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Would remove/reduce risk of entanglement and is a low cost monitoring capability.
Tidal	Design feature	Operation & Maintenance	Lighting	Birds	Seabirds	Potential for lighting to adversely affect nocturnal and migratory species.	Consider type, colour and use of lighting during design and consultation with navigational stakeholders.	A targeted lighting plan may have the potential to reduce impacts on sensitive species but navigational safety takes precedence.
Tidal	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Would remove/reduce risk of transfer and settlement of non-native species.
Wave	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Installation	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Tidal	Monitoring	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Tidal	Mitigation	Installation	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Do not break up or 'flush' rafts of birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Also pertinent to note that the measure is selectively applied to project vessels in context of other vessel operations.
Tidal	Mitigation	Decommissioning	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Adhere to minimum approach distances for vessels on approach to marine mammals and birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Can increase the time of operational procedures and thus increase cost. Further monitoring, e.g. defining of approach distances and then comparing these to see which are most effective would validate the efficacy of the measure.
Wave	Mitigation	Decommissioning	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Vessel transit route: defining routes to avoid sensitive sites and to only disturb one route.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Installation	Changes in sediment dynamics	Fish	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Monitoring	Operation & Maintenance	Collision risk	Fish	Fish	Potential for collision with turbine blades.	Environmental monitoring to better understand near-field behaviour and avoidance.	This will help reduce scientific uncertainty, however this type of monitoring can be expensive and there are difficulties associated with storing and analysing the data produced.
Wave	Mitigation	Installation	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. Alrhough, use of lower toxicity materials may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Decommissioning	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Compliance	Operation & Maintenance	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Elasmobranchs	Impacts of electromagnetic fields from subsea cables on sensitive species.	Use of 3-phase cables instead of DC cables.	Reduce the level of EMF to surrounding water column and therefore any potential effects. Potential commercial and technical feasibility issues some disagreement as to efficacy of this measure.
Wave	Design feature	Installation	EMF and thermal pressure	Fish	Migratory fish	Impacts of electromagnetic fields from subsea cables on sensitive species.	Micrositing to avoid sensitive habitats & minimise footprint.	This could reduce/remove effects on sensitive habitats and is a relatively low cost measure.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Lay cables in natural crevices.	n/a
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive species.	Bury cables where possible and viable.	n/a
Wave	Monitoring	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in device mooring lines and cables.	Install tension sensors on mooring lines.	Informs of problem with mooring lines allowing rectification, however their implementation would come at an additional cost and would require control system integration.
Wave	Monitoring	Operation & Maintenance	Entanglement	Fish	Basking shark; Large fish	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Would remove/reduce risk of entanglement and is a low cost monitoring capability.
Wave	Design feature	Installation	Loss of habitat	Fish	Demersal fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Micrositing of offshore infrastructure to avoid sensitive habitats.	This could reduce/remove effects on sensitive habitats and is a relatively low cost measure.
Wave	Design feature	Installation	Loss of habitat	Fish	Demersal fish	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Cable protection management measures to ensure that any rock placement that is required will be kept to a minimum to reduce seabed disturbance.	This could reduce effects on sensitive habitats.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/removes risk of transfer of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/removes risk of transfer of non-native species.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/removes risk of transfer of non-native species.
Wave	Monitoring	Decommissioning	Marine Non-Native Species (MNNS)	Fish	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Wave	Monitoring	Operation & Maintenance	Underwater noise	Fish	Fish	The potential effects from underwater noise generated by wave and tidal energy converters.	Measure noise generated by device(s) during operation to better understand the potential effects on sensitive species.	Measured noise levels can be correlated with threshold values of relevant species to determine impact and need for adaptive management measures. It can be complex and costly to undertake this type of monitoring in high energy environments.
Wave	Mitigation	Operation & Maintenance	Vessel disturbance	Fish	Large fish	Potential for disturbance from project vessels.	Use smaller vessels for maintenance purposes.	Reduces potential effects and is a relatively low cost measure.
Wave	None identified	Operation & Maintenance	Barrier to movement	Marine Mammals	All receptors	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Tidal	Mitigation	Installation	Changes in sediment dynamics	Marine Mammals	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Mitigation	Operation & Maintenance	Collision risk	Marine Mammals	Marine Mammals	Potential for collision with turbine blades.	Install acoustic deterrent devices (ADDs).	This could potentially reduce likelihood of collision with moving blades although the efficacy of ADDs in these environments is unknown. Constant deterring means habituation is likely. This is a simpler system than detect (efficiently) and deter, however would still be expensive to implement. It would also come with an additional noise impact which must also be considered in project assessments.
Wave	Design feature	Decommissioning	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Operation & Maintenance	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Installation	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event, ensures that contingency plans are in place and demonstrates compliance with environmental management systems.
Wave	Compliance	Decommissioning	Contamination	Marine Mammals	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event, ensures that contingency plans are in place and demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in device mooring lines and cables.	Cable design with maximum bend radius.	Removes/reduces risk of entanglement, however cable design tends to be driven by technical and commercial consideration.
Wave	Monitoring	Operation & Maintenance	Entanglement	Marine Mammals	Cetaceans	Potential for marine animals to become entangled in lost fishing gear or other equipment trapped on infrastructure.	Ensure standard notifications of loss of fishing gear in region notified to operators. Reporting of entanglement events.	Good practice for emergency preparedness.
Wave	Mitigation	Operation & Maintenance	Entrapment	Marine Mammals	All receptors	Potential risk of entrapment within device chambers and mooring arrays.	Release entrapped animal.	Animal may be deceased before it is able to be released.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Marine Mammals	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Mitigation	Installation	Underwater noise	Marine Mammals	Marine Mammals	The potential effects from underwater noise generated during installation/ construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, however may could increase project construction timescales e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Wave	Mitigation	Decommissioning	Vessel collision	Marine Mammals	Cetaceans	Potential for collision with project vessels.	Adhere to minimum approach distances for vessels on approach.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Operation & Maintenance	Vessel disturbance	Marine Mammals	Marine Mammals	Potential for disturbance from project vessels.	Reduce speed and maintain steady course when animal is sighted.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Operation & Maintenance	Vessel disturbance	Marine Mammals	Seals	Disturbance at seal haul-out sites from project vessels.	Avoid transiting within 500m of known seal haul outs.	Reduces potential effects and is a relatively low cost measure.
Wave	None identified	Operation & Maintenance	Barrier to movement	Reptiles	All receptors	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Tidal	Mitigation	Installation	Changes in sediment dynamics	Reptiles	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Mitigation	Installation	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. Although, use of lower toxicity materials may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Decommissioning	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Mitigation	Operation & Maintenance	Contamination	Reptiles	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	Entanglement	Reptiles	Sea turtles	Potential for marine animals to become entangled in device mooring lines and cables.	Maintain taut mooring lines.	Removes/reduces risk of entanglement, however mooring design is driven by technical and economic consideration. An entanglement record is a good way to track events.
Wave	Monitoring	Operation & Maintenance	Entanglement	Reptiles	Sea turtles	Potential for marine animals to become entangled in device mooring lines and cables.	Routine inspections of mooring lines. Implement features into existing control systems to detect entanglement events.	Removes/reduces risk of entanglement and is a low cost monitoring capability.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduces/removes risk of transfer and settlement of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduces/removes risk of transfer and settlement of non-native species.
Wave	Monitoring	Decommissioning	Marine Non-Native Species (MNNS)	Reptiles	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduces/removes risk of transfer of non-native species.
Tidal	Mitigation	Installation	Changes in sediment dynamics	Habitat	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Operation & Maintenance	Changes in sediment dynamics	Habitat	Benthic species	The potential wider or secondary effects (siltation changes or smothering) on protected or sensitive littoral habitat due to devices and associated moorings, support structures or landfall cables.	Micrositing of landfall cables and infrastructure to minimise the impact on sensitive habitats and species. Best practice techniques for cable installation, burial and protection.	n/a
Tidal	Design feature	Decommissioning	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Wave	Mitigation	Operation & Maintenance	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Mitigation	Installation	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Compliance	Decommissioning	Contamination	Habitat	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer and settlement of non-native species.
Tidal	Mitigation	Operation & Maintenance	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Habitat	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Source vessels locally.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Monitoring	Operation & Maintenance	Changes in sediment dynamics	Benthic	Fish, Benthic invertebrates	The potential wider or secondary effects (siltation changes or smothering) on protected or sensitive sub-littoral seabed due to scour or siltation around devices and associated moorings, support structures and export cables.	Periodic visual monitoring through the use of divers or drop down video, static cameras / remote sensing techniques, benthic grab surveys, geophysical survey to identify scour pits, turbidity measurements.	Implementation of this measure would generate data to quantify level and spatial extent of effect, however there are technical and health and safety risks associated with periodic monitoring in close vicinity of infrastructure. This measure may also require power shut down. Additionally, the associated subsea static monitoring options require O&M which has potential time and cost implications.
Tidal	Mitigation	Installation	Changes in sediment dynamics	Benthic	All receptors	Reduced visibility from altered water clarity associated with sediment mixing that can impact prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Operation & Maintenance	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Installation	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Decommissioning	Contamination	Benthic	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from subsea cables on sensitive species.	Install cable protection/ armor/ rock placement/ other cable protection.	Reduces the level of EMF to surrounding water column and therefore any potential effects. Reduces 'snagging risk' for vessels and may create habitat for species. May have Habitat Creation implications Potential for adverse impacts on surrounding benthic habitats and sensitive species, e.g. from smothering. This measure forms part of normal project design.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from subsea cables on sensitive species.	Bundle cables together to reduce field vectors.	Reduces the level of EMF to surrounding water column and therefore any potential effects, however there is potential for less redundancy in the system together with potential commercial and technical feasibility issues.
Wave	Design feature	Installation	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species.	Micrositing of offshore infrastructure to avoid sensitive habitats and minimize footprint.	This could reduce/remove effects on sensitive habitats and can often be done with little additional cost.
Wave	Design feature	Operation & Maintenance	EMF and thermal pressure	Benthic	Benthic invertebrates	Impacts of electromagnetic fields from landfall cables on sensitive species	Bury cables where possible and viable	n/a
Tidal	Design feature	Installation	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices associated moorings or support structures on the seabed.	Micrositing of offshore infrastructure to avoid sensitive habitats.	This could reduce/remove effects on sensitive habitats and can often be done with little additional costs.
Tidal	Design feature	Installation	Loss of habitat	Benthic	Benthic invertebrates	Direct loss of protected or sensitive sub-littoral seabed communities due to the presence of devices and associated moorings or support structures on the seabed.	Cable protection management measures to ensure that any rock placement that is required will be kept to a minimum to reduce seabed disturbance.	This could reduce effects on sensitive habitats.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Compliance	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Compliance with all relevant guidance (including IMO guidelines) regarding ballast water management and transfer of non-native species.	Reduce/remove risk of transfer and settlement of non-native species.
Wave	Monitoring	Installation	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Wave	Compliance	Decommissioning	Marine Non-Native Species (MNNS)	Benthic	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Monitoring and reporting of MNNS.	Reduce/removes risk of transfer of non-native species.
Wave	None identified	Operation & Maintenance	Barrier to movement	Birds	Birds	Potential barrier to movement due to the physical presence of devices and associated moorings / support structures, cables and electrical equipment.	None identified.	n/a
Tidal	Mitigation	Installation	Changes in sediment dynamics	Birds	All receptors	Sediment disturbance disrupting water clarity that results in smothering of fish spawning grounds.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Wave	Design feature	Decommissioning	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Physical Containment systems including bulk heads, closed circuit systems, pressure relief systems.	Reduces risk of contamination escaping from structure.
Tidal	Mitigation	Operation & Maintenance	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. However, use of lower toxicity may compromise performance, or impact other technical issues (e.g. fluid changes).
Wave	Mitigation	Installation	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Compliance	Decommissioning	Contamination	Birds	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Wave	Design feature	Operation & Maintenance	Entanglement	Birds	Diving birds	Potential for marine animals to become entangled in device mooring lines and cables.	Fishing debris detected during routine inspections of mooring lines and cables will be removed.	Would remove/reduce risk of entanglement and is a low cost measure, implemented as part of standard O&M procedures.
Wave	Mitigation	Operation & Maintenance	Entanglement	Birds	Diving birds	Potential for marine animals to become entangled in lost fishing gear or other equipment trapped on infrastructure.	Fisheries management: Agreement with fishermen not to fish near to the device, warning of the dangers of losing equipment.	Reduces potential for entanglement of fishing gear in mooring lines and thus potential for entanglement of marine animals.
Wave	Mitigation	Installation	Lighting	Birds	Seabirds	Potential for light from installation vessels to adversely affect nocturnal and migratory species.	Limit lighting on installation vessels to that safe for navigational purposes only.	Reduce impact on sensitive species. A lot of the light on navigational vessels is superflous so would not detract from their safe operation.
Wave	Mitigation	Installation	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Establish and implement a Biofouling Management Plan.	Reduce/remove risk of transfer of non-native species.
Wave	Mitigation	Decommissioning	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Tidal	Compliance	Operation & Maintenance	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Adhere to appropriate measures when jettisoning ballast water.	Reduce/remove risk of transfer of non-native species.
Wave	Design feature	Installation	Marine Non-Native Species (MNNS)	Birds	All receptors	Potential for introduction of MNNS which can have an adverse impact on the native species at the site.	Avoid the introduction of hard bottom substrate into a soft bottom habitat.	Ensures the efficient recovery of species native to the surrounding habitat. May have technical implications.
Wave	Mitigation	Installation	Underwater noise	Birds	Seabirds	The potential effects from underwater noise generated during installation/ construction (excluding piling).	Avoid/limit 'noisy works' within close proximity to sensitive sites i.e. known seal haul outs during sensitive periods, defining appropriate clearance distances where necessary.	This could reduce potential effects on sensitive species during sensitive periods, but could increase project construction timescales and thus costs e.g. if continuous drilling time is restricted or specific periods need to be avoided.
Tidal	Mitigation	Operation & Maintenance	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Do not break up or 'flush' rafts of birds.	Reduces potential effects and is a relatively low cost measure, however effectiveness of mitigation is unclear. Also pertinent to note that the measure is selectively applied to project vessels in context of other vessel operations.
Wave	Mitigation	Installation	Vessel disturbance	Birds	Shore-nesting birds	Potential for disturbance from project vessels.	Avoidance of sensitive shore nesting areas during sensitive periods with appropriate clearance distance.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Installation	Vessel disturbance	Birds	Birds on water	Potential for disturbance from project vessels.	Vessel transit route: defining routes to avoid sensitive sites and to only disturb one route.	Reduces potential effects and is a relatively low cost measure.
Tidal	Mitigation	Decommissioning	Changes in sediment dynamics	Fish	All receptors	Reduced visibility impacting prey detection and obstruction avoidance.	Best practice methodologies to reduce resuspension of sediment during cable burial or device foundation / mooring installation.	n/a
Tidal	Mitigation	Operation & Maintenance	Collision risk	Fish	Fish	Potential for collision with turbine blades.	Selective structural and blade coatings i.e. colours to aide detection.	Unknown - it is possible that this will aid detection of subsea structures and help reduce risk although further research is needed - certain colours may serve to attract fish and lead to an increase in collision risk. A small one off cost that can be easily planned for at the design stage.
Wave	Mitigation	Operation & Maintenance	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Material selection - lubricants, coolants, hydraulic fluids etc. selected with low ecotoxicity levels and biodegradable.	Reduces/removes risk of contamination from materials which may have escaped structure. Alrhough, use of lower toxicity materials may compromise performance, or impact other technical issues (e.g. fluid changes).
Tidal	Mitigation	Installation	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Where rock placement is used, ensure clean rock is used.	Reduces/removes risk of contamination from materials.
Tidal	Compliance	Decommissioning	Contamination	Fish	All receptors	Potential for accidental or unplanned events which could lead to contamination of the marine environment.	Management: Establish and implement a Contamination Control Plan / Ship Oil Contamination Emergency Plans (SOPEPs). Compliance with International Maritime Organisation (IMO) and Maritime Coastguard Agency (MCA) codes for the prevention of contamination.	Reduces risk of any contamination event and ensures that contingency plans are in place. Demonstrates compliance with environmental management systems.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Elasmobranchs	Impacts of electromagnetic fields from subsea cables on sensitive species.	Use of 3-phase cables instead of DC cables.	Reduce the level of EMF to surrounding water column and therefore any potential effects. Potential commercial and technical feasibility issues some disagreement as to efficacy of this measure.
Tidal	Design feature	Installation	EMF and thermal pressure	Fish	Migratory fish	Impacts of electromagnetic fields from subsea cables on sensitive species.	Micrositing to avoid sensitive habitats & minimise footprint.	This could reduce/remove effects on sensitive habitats and is a relatively low cost measure.
Tidal	Design feature	Operation & Maintenance	EMF and thermal pressure	Fish	Demersal fish	Impacts of electromagnetic fields from landfall cables on sensitive specie