OES-Environmental distributes metadata forms (questionnaires) to solicit information from developers involved in environmental monitoring around marine renewable energy project sites around the world. This page provides project descriptions, baseline assessment, post-installation monitoring, and links to available data and reports. Content is updated on an annual basis.

Anglesey Skerries Tidal Stream Array

Project Site OES-Environmental

Title: Anglesey Skerries Tidal Stream Array
Research End Date:
March 01, 2016
Technology Type:
Info Updated:
September 13, 2018
AR Series Turbine being lifted with a crane.
Project Status: 
Device never deployed
Atlantis AR Series
Project Scale: 
Commercial array
Installed Capacity: 
10 MW

Site selection, feasibility assessments and environmental studies began in 2006 and a newly created development company, SeaGeneration (Wales) Ltd, was set up in 2008 as a joint venture between Marine Current Turbines (MCT) and RWE npower renewables to develop the project. MCT was subsequently bought over by tidal industry leader Atlantis Resources Ltd in 2015. The location for the proposed array was a 0.56 km2 site between the group of rocks and islands known as the Skerries and Carmel Head.  The site is less than 1km from the Anglesey coast and is characterised by water depths of around 20 to 40 m.  Its close proximity to Holyhead made the site suitable due to access to good port facilities, the national grid and transport connections. The proposed array was planned to consist of up to 9 SeaGen devices and have a total installed capacity of up to 10 MW.  The array was planned to operate for up to 25 years and serve as a test case for the development of the technology in multi device arrays.


The technology used was to be the Atlantis AR Series Turbines, which are commercial-scale horizontal axis turbines designed for open ocean deployment in the most energetic marine environments on the planet. The Atlantis AR turbines are currently available in a 1.5 MW AR1500 system designed by Lockheed Martin Corporation, and the 1.5 MW SeaGen U system, both with active pitch configuration and yaw capability. AR series turbines are deployed using a patented stab system that facilitates rapid deployment, retrieval and subsea connection to shore.


Key design Features of the AR tidal turbine systems include:

  • A single axial flow rotor that drives a generator via a gearbox - much like a  wind turbine
  • Complex electrical infrastructure such as converters are located on the shore to reduce the amount of electrical equipment contained offshore
  • Stab system enables rapid retrieval without having to recover the foundation structure - for ease of maintenance
  • AR series turbine systems produce fully grid compliant power

Export cable:

A single 33 kV export cable was to be laid to transport generated power to the shore. Two possible cable corridors 500 m in width were identified and assessed, with three methods considered

for the installation of the export cable.  The first option involved laying the cable directly onto the seabed; this method would have left the cable vulnerable to physical damage from fishing gear and rocks / coarse sediment circulated by the strong currents. The second available option was trenching the cable using a plough.  It was likely that this method would only take place in the intertidal sections of the cable route. The final option was directional drilling.  A directional drill would have created a hole in the bedrock from the land to a point approximately 1km from the proposed array. The cable would then either be entrenched or covered with protective mattresses for the remainder of its route.


Between Skerries and Carmel Head on mainland Anglesey.

Coordinates: The four corners of the cancelled development site are labeled as A1, A2, A3 and A4:

  Easting Northing
A1 395560 5919420
A2 395007 5919998
A3 395512 5920482
A4 396066 5919905


Project Timeline: 

Consent for the project had been granted and a grid connection for 2015 secured, with onshore work underway including feasibility studies and assessment of options for an export cable route, landfall point and substation location. However, the project was shelved in September 2014 after MCT/Siemens suspended the project with no re-start date.

However, in April 2015 it was announced that industry leader Atlantis had reached an agreement to acquire the entire issued share capital of the Bristol-based tidal business MCT from Siemens AG in an all share deal. This purchase included a portfolio of six projects including the Skerries scheme.

Despite the purchase of MCT’s/Siemens’ portfolio of sites by Atlantis, it was announced in March 2016, that they would relinquish the Agreements for Lease that it held at two of these sites, one of which was Anglesey Skerries (the other being the Kyle Rhea site in Scotland). Ownership of these sites has now returned to The Crown Estate.

Atlantis stated that they wished to prioritise other sites that are currently under construction and closer to reaching financial close.

Licensing Information: 

In March 2014 an EIA consent decision under the Marine Works (Environmental Impacts Assessment) Regulations 2007 was issued to SeaGeneration (Wales) Ltd by Natural Resources Wales on behalf of the Licensing Authority. This consent decision can be accessed here.

Licence Competent Status
Section 36 (Electricity Act) Consent N/A N/A
Marine Licence (Marine (Scotland) Act) Consent N/A N/A
Licence to Disturb Marine Species N/A N/A
Licence to Disturb Basking Shark N/A N/A
Town and County Planning Permission N/A N/A


Key Environmental Issues: 

The following potential impacts were identified as being potentially significant during the EIA:


  • Erosion or accretion of shoreline at landfall within SSSI
  • Operational noise causing disturbance and barrier effect to marine mammals
  • Collision risk between marine mammals and device
  • Operation of the device causing displacement of fishing activities
  • Device presence disturbing seascape from a number of view points
  • Collision risk of vessels transiting through the area 


Mitigation measures:


The following mitigation measures were outlined in the Environmental Statement:


  • Scour protection will be considered for areas where significant scour is recorded to prevent any further erosion and associated release of potential suspended sediments.
  • Any trenching will be backfilled immediately to reduce impact of suspended sediment on benthos, fish and shellfish during construction.
  • Marine mammal observer will be present during construction to identify disturbance or injury to marine mammals, basking sharks and marine turtles caused by noise or collision with vessels.
  • Deploy and monitor strategy to protect marine mammals from the effects of operational noise, habitat exclusion, collision risk, and barrier effect of the array will be developed.


Environmental webpage: http://www.seagenwales.co.uk/environmental-aspects/


Anglesey Skerries Tidal Stream Array is located in United Kingdom.

Baseline Assessment: Anglesey Skerries Tidal Stream Array

General Description:

The following field surveys were undertaken (or commissioned by) the developer to inform baseline characterisation

ReceptorStudy Description Design and Methods Results Status
  • Physical Environment

Geophysical survey by EMU Ltd. in 2008.

Seabed surface sediments have been investigated through geophysical and bathymetric surveys. Bathymetry, interpreted seabed surface geology and isopach were included in the survey.

The survey reported that depth variations across the site appeared to correspond not only to exposed bedrock but also fingers of mobile and static sediment within the area.  Coarse sand and bedrock dominated the central and western region of the surveyed area.  Surrounding this area were regions that contained cobbled silt, gravelly pebbly cobbles, sandy gravel and cobbly sand.  Bedforms with a maximum wave height of 2m have been identified in the surveyed area and have their long axis generally orientated NNW-SSE.  Pockets of sediment infilling the surface topography of the bedrock were clearly identified

  • Intertidal Ecology

MACS visual intertidal habitat survey and faunal analysis of sediment cores

A walkover survey of Carmel Head was conducted followed up with a detailed survey of Hen Borth.

The results from the intertidal survey found the coast around Carmel Head (cable route option 1) to be typically steep rock faces supporting dense communities of kelps on the lower shore, fucoid algae on the mid-shore in sheltered embayments and upper shore all along the coast, barnacles and mussels on the mid-shore on exposed headlands and lichen in the splash zone. There are occasional narrow, steep-sided embayments which end on the landward side in shores of fucoid-covered boulder on the lower shore and clean shingle on the upper shore. In addition, there are several points of cave or overhang biotope which may constitute Annex I habitat.

  • Benthos

Site specific benthic survey

Drop down camera at sites pre-determined from geophysical data. Grabs attempted but failed due to hard substratum.

The site-specific benthic survey identified fifteen biotopes (including one subdivision) in four main habitat types, plus one Sabellaria spinulosa biotope at one of the western reference stations and a further four identified from the potential cable route into Cemlyn Bay.

  • Marine Mammals

Surveys commissioned by the Welsh Assembly Government

Vessel based observations and acoustic surveys using static acoustic monitoring devices. Results provided in the report by Gordon et al. 2010.

Several marine mammal species occur in the region. Over twenty species of cetacean can be seen around the Welsh coastline and of these five species are known regularly to occur. These are harbour porpoises (Phocoena phocoena), bottlenose dolphins (Tursiops truncatus), short-beaked common dolphins (Delphinus delphis), Risso’s dolphins (Grampus griseus) and minke whales (Balaenoptera acutorostrata). Two species of seal also occur on the welsh coast, the grey seal (Halichoerus grypus) and harbour (or common) seal (Phoca vitulina). Relatively high densities of harbour porpoise within the area.

  • Birds

SeaGen commissioned vantage point surveys

Each survey consisted of 3 hours of continuous diurnal observations from two vantage points on Carmel Head. Eight surveys per vantage point per month were carried out between April and September 2009.

A total of 20 species of seabird and five species of seaduck were recorded crossing the Project Site in April – September 2009 by the Seabird surveys. The majority of birds recorded were Manx Shearwater, Auk species (Razorbill and/or Guillemot), Gannet and Herring Gull with these five species comprising over 70% of all birds counted. The majority of individual birds (84%) that were observed transiting the Project Site were flying in close proximity to the adjacent coastline.

Reports and Papers


Post-Installation Monitoring: Anglesey Skerries Tidal Stream Array

General Description:

The following monitoring measures are proposed within the Environmental Statement

ReceptorMonitoring Program Description Design and Methods Results Status
  • Physical Environment

Post installation Bathymetric swathe survey.

Survey of the seabed within 100 m of each SeaGen device and along a 100 m corridor centred on all cable routes where surface laid, to be carried out pre and post construction. A further period of surveys may be deemed necessary on agreement with the Regulator if seabed instabilities are identified.

  • Physical Environment

Beach survey.

Beach survey within 50 m of the landfall, to be carried out pre and post construction, if the cable is surface laid. A further period of surveys may be deemed necessary on agreement with the Regulator if ongoing beach change is predicted and deemed to be an issue.

  • Intertidal Ecology

Shore survey.

Walk over survey and a core sample survey analysis of the softer sediments, including repetition of the sites surveyed for this assessment. Surveys will follow JNCC standard biotope methodology. Results will be published and submitted to the statutory authorities.

  • Benthos

Camera or diver surveys.

Camera or diver survey in combination with benthic grabs for areas of soft-sediments of the main site and cable route (inshore sites only where sediment type is feasible for grabs). These surveys will be undertaken as a baseline and repeated during and after construction.

  • Benthos

Chemical sampling of any soft sediment present

To test for contaminants which may be released into the marine system during construction e.g. trenching of the cable at inshore areas.

  • Benthos

Camera or diver surveys.

A survey using camera or divers to record evidence of colonisation of the structure, rock armour and scour protection and also to record any evidence of scour.

  • Fish


Monitoring will be discussed and agreed with the statutory authorities prior to construction.

  • Marine Mammals

Visual monitoring

Visual monitoring of marine mammal activity around the array pre and post installation to look for evidence of changes in use of the area.

  • Marine Mammals

Acoustic monitoring

Passive acoustic monitoring of echo locating species using the area of the development as well as the ‘coastal corridor’ to the south of the proposed array.

  • Marine Mammals

Visual sea surveys

Surveys of local grey seal haul out sites along with pup production surveys.

  • Marine Mammals

Strike detection monitoring.

On-going remote monitoring of SeaGen rotor strike detection system. This will provide an incident alarm if there are any collisions with the rotor, with the ability for remote shutdown should a mammal strike be confirmed.

  • Birds

No monitoring required given the predicted negligible impact and low bird abundance on the site.

  • Fisheries

Regular interviews with commercial fishermen.

To determine: whether the additional vessel traffic associated with the array has an adverse effect on fishing activity; the status of commercial fisheries in the area relative to current conditions to assess any indirect effects of array; and if the array has had an adverse effect on the use of pots in adjacent waters.

  • Vessel Navigation

Review of operation hazards.

Regular review of the operation and hazards will be undertaken and any necessary modification to procedures will be carried out.

  • Visual Landscape

No future monitoring measures are proposed.

Reports and Papers N/A
Research N/A
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