Understanding the Potential for Marine Megafauna Entanglement Risk from Marine Renewable Energy Developments


Title: Understanding the Potential for Marine Megafauna Entanglement Risk from Marine Renewable Energy Developments
Publication Date:
January 01, 2014
Document Number: 791
Pages: 95

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Website: External Link
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Benjamins, S.; Harnois, V.; Smith, H.; Johanning, L.; Greenhill, L.; Carter, C.; Wilson, B. (2014). Understanding the Potential for Marine Megafauna Entanglement Risk from Marine Renewable Energy Developments. Report by Scottish Natural Heritage. pp 95.

The global marine renewable energy (MRE) industry (including offshore wind, wave and tidal energy) is developing rapidly, particularly in Scotland where the Scottish Government is driving growth of the industry as part of their sustainable development agenda. As increasing numbers of devices are set to be deployed, concerns have been raised over potential environmental impacts. One such potential impact of marine renewable energy development is the risk of whales, basking sharks and other large animals (“marine megafauna”) becoming entangled in mooring systems and associated power cables. Given the widespread occurrence of marine megafauna injury and mortality through entanglement and bycatch in fishing gear, the issue poses potentially serious conservation concerns.


Main findings


The present report set out to review existing information on entanglement risks to marine megafauna posed by moorings. Based on an extensive literature review, it was concluded that moorings such as those proposed for MRE devices will likely pose a relatively modest risk in terms of entanglement for most marine megafauna, particularly when compared to risk posed by fisheries. Nevertheless, some circumstances were identified where moorings associated with MRE devices could potentially pose a risk, particularly, 1) in cases involving large baleen whales and, 2) if derelict fishing gears become attached to the mooring, thereby posing an entanglement risk for a wide range of species (including fish and diving seabirds).


In the absence of significant amounts of empirical data, a qualitative risk assessment approach was developed to assess relative risks to marine megafauna groups on the basis of biological and physical risk parameters. Biological risk factors included body size, animals’ ability to detect moorings, animals’ body flexibility and general feeding modes. Physical risk factors were defined as mooring tension characteristics, swept volume and curvature. Mooring behaviours were dynamically modelled for six different mooring types (catenary [three different compositions], catenary with accessory buoy, taut, taut with accessory buoy) using OrcaFlex™ software to assess the physical risk factors under different sea states. In order to inform the risk assessment, biological and physical risk factors were combined to populate a relative risk matrix for all modelled moorings.


Results suggest that for most megafauna, MRE device moorings are unlikely to pose a major threat; however, it should be remembered that cetaceans (as European Protected Species) and basking sharks are afforded legal protection at the individual level in Scotland and therefore should be considered accordingly. Baleen whales were considered to be at greatest relative risk overall, largely due to their size and foraging habits. Some mooring designs presented a greater relative risk than others, with the greater relative risks generated by catenary moorings, particularly those containing nylon. Taut systems represented the lowest relative risk. Most moorings associated with MRE devices would likely be too strong for animals to easily break free if they became entangled. Entanglement risks among MRE arrays will likely vary substantially based on device spacing, mooring design and array layout.


Currently MRE development proposals often vary in the degree of detail provided about the moorings’ physical properties, complicating attempts by regulators to assess different mooring systems for entanglement risk. The qualitative risk assessment approach described in this report enables device developers and regulatory bodies to assess potential entanglement risks at an early stage of the development of a MRE proposal, allowing appropriate risk management and enabling mitigation strategies to be developed if necessary.


Recommendations include the following:

  • When submitting a development proposal, developers should be encouraged to follow the relative risk assessment process outlined in this report, and to provide details of existing and planned routine inspection regimes involving moorings.
  • During the consent period of devices and arrays, a procedure needs to be put in place which would require developers to report to regulators any significant changes to mooring and MRE device behaviour over time if such changes would increase the risk of marine megafauna entanglement.
  • There is a need for the establishment of an official reporting mechanism by which developers can report the presence of marine megafauna entanglement in MRE device moorings to the regulator (e.g. Marine Scotland who will need to be aware for HRA and EPS purposes).
  • A formal accident investigation procedure needs to be put in place by the developer, in order that in the event of an entanglement the appropriate authorities are alerted to allow all relevant information to be recorded, and to trigger an assessment by the regulator into whether any emergency measures were required.
  • Details of moorings relevant to the risk of entanglement of marine megafauna should be included alongside Marine Licence applications and within Environmental Statements.
  • Further investigations are needed to clarify the distribution and abundance of derelict fishing gear in Scottish waters, and the extent to which gear becomes snagged in moorings or other vertical structures in the water column.
  • Further research may be required to assess the full range of entanglement mitigation options available to the MRE industry, to minimise any risks of entanglement events occurring.
  • Further research may be required to assess the effects of redistribution of fishing effort displaced from MRE development sites, to ensure that marine megafauna entanglement/bycatch risks are not merely displaced or exacerbated elsewhere as a result.
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