REVIEW OF REEF EFFECTS OF OFFSHORE WIND FARM STRUCTURES AND POTENTIAL FOR ENHANCEMENT AND MITIGATION JANUARY 2008 IN ASSOCIATION WITH Review of the reef effects of offshore wind farm structures and potential for enhancement and mitigation Report to the Department for Business, Enterprise and Regulatory Reform PML Applications Ltd in association with Scottish Association of Marine Sciences (SAMS) Contract No : RFCA/005/00029P This report may be cited as follows: Linley E.A.S., Wilding T.A., Black K., Hawkins A.J.S. and Mangi S. (2007). Review of the reef effects of offshore wind farm structures and their potential for enhancement and mitigation. Report from PML Applications Ltd and the Scottish Association for Marine Science to the Department for Business, Enterprise and Regulatory Reform (BERR), Contract No: RFCA/005/0029P Acknowledgements Acknowledgements The Review of Reef Effects of Offshore Wind Farm Structures and Potential for Enhancement and Mitigation was prepared by PML Applications Ltd and the Scottish Association for Marine Science. This project was undertaken as part of the UK Department for Business, Enterprise and Regulatory Reform (BERR) offshore wind energy research programme, and managed on behalf of BERR by Hartley Anderson Ltd. We are particularly indebted to John Hartley and other members of the Research Advisory Group for their advice and guidance throughout the production of this report, and to Keith Hiscock and Antony Jensen who also provided detailed comment on early drafts. Numerous individuals have also contributed their advice, particularly in identifying data resources to assist with the analysis. We are particularly indebted to Angela Wratten, Chris Jenner, Tim Smyth, Mark Trimmer, Francis Bunker, Gero Vella, Robert Thornhill, Julie Drew, Adrian Maddocks, Robert Lillie, Tony Nott, Ben Barton, David Fletcher, John Leballeur, Laurie Ayling and Stephen Lockwood – who in the course of passing on information also contributed their ideas and thoughts. We are also grateful to BERR for providing us with the opportunity to undertake what has proved to be an interesting and rewarding research project. iii Review of the reef effects of offshore wind farm structures and potential for enhancement and mitigation Executive Summary The purpose of this report is to review the likely reef effects of offshore wind farm (OWF) structures focussing on two aspects of their physical presence: firstly, the likely reef effects on fish, shellfish and other marine biota and secondly, the potential to enhance the reef effect for commercially significant species. The report begins with a literature review of the factors which control colonisation of structures in the marine environment, and describes the characteristics of the subsequent succession and climax communities. Predictions of the enhanced habitat opportunities for commercially important species (such as mussels, lobster, crab and finfish) associated with OWFs in the UK, were then considered. We used a combination of existing data resources and an understanding of the life cycles, food requirements and physiology of the target species, together with simple mathematical considerations, to assess whether such opportunities might present themselves, either through provision of shelter or rocky substrata on which to settle, and/or adequacy of food supply. We have extended our analysis to include some preliminary observations on the aquaculture potential of OWFs. The report also considers the potential offered by the footprints of OWF, together with their turbine structures and associated scour protection, to enhance the opportunities for local fisheries, either through enhanced habitat opportunities for commercial species or through the development of ‘no-take’ areas. As a general rule, our analysis shows that for each Round 2 OWF site identified, we are able to recommend, on the basis of predictions from existing data, the development of commercial activities which are likely to yield useful outcomes and identify others which are unlikely to succeed. However, more detailed site based investigations would be needed to verify the predictions before developing any enterprise commercially. The following table summarises the potentially enhancing/mitigation effects of OWF structures and their associated scour protection for individual species, and provides further comment on potential with regard to fisheries management measures. These tentative assessments can be updated as further information becomes available to ground-truth the predictions. iv Executive Summary Table 1: Summarising the potentially enhancing/mitigation effects of OWF structures and their associated scour protection in Round 2 areas North-west (Solway The Greater Wash Thames Estuary to North Wales coast) (Wash to Humber) Potentially enhancing effects of artificial reefs Cancer pagurus1,2 +++ Homarus gammarus1,2 +++ Mytilus edulis1,2,4 0 to + 0 to + 0 to (+) Crassostrea gigas1,2,4 0 to + 0 to + 0 to (+) Laminariales1,2,3,5 ++0 Finfish1,2,5 0 to + 0 to + 0 to + Note: + positive; – negative; 0 neutral 1 Evidence from baseline surveys (diverse sites and sources); 2 Evidence from Post construction monitoring surveys; 3 Evidence from wind farm analogues e.g. Sarns; 4 Evidence from existing shellfish models; 5 Evidence from literature Potential for enhancing fisheries resources Closure of OWF footprint There is evidence to indicate that juveniles of some species preferentially use to extend protection of rocky reefs as habitat including, potentially, turbine bases and associated rock nursery and spawning armouring e.g. whiting, crabs (post burrow stage) and lobsters. The beneficial areas effects of closure could be tested at an existing OWF site where known nursery areas extend into the OWF footprint. It may be easier to enforce closure to fishing activity within an OWF footprint rather than outside; currently and in common with structures like oil platforms in the North Sea, exclusion zones operate at some OWF sites around turbines (50m). Closure to some fishing gears could be negotiated with local fishermen, and implemented by a SFC byelaw (within 6 nm) or ministerial (SI) Statutory Instrument (out to 12 nm). Closure (partial ‘no- It is very unlikely that all types of fishing gear need to be excluded from OWF take’) to assist in the footprints for operational reasons – however, measures to exclude particular recovery/enhancement/ fishing gears combined with knowledge of habitat preferences of target species management of specific might be used to assist recovery of specific commercially valuable species at some commercially important sites, e.g. cod, bass/whiting. There is evidence to suggest that turbines plus reefs fin fish species may offer direct benefits for these species. This partial closure option does not exclude the possibility of developing for e.g. bass restoration areas to support recreational sea angling at some locations such as in the Thames Estuary. Partial closure of OWFs could be implemented under current byelaws administered by SFCs or negotiated with local fishermen. Closure of OWF footprint Closure of OWF footprints, as part of a wider strategic network of Marine i.e. ‘no-take’ MPA Protected Areas (MPAs) to support fisheries management, could have significant enhancement/mitigating potential for local fisheries. As yet, to our knowledge, there have been no studies in UK waters which have set out to assess the effects of closing an area of sea space, such as the footprint of an OWF, to all exploitative activity other than those carried out at Lundy, where lobsters are more numerous and larger than before the introduction of the no-take zone. However, there is evidence to suggest that not only will stocks of fish increase within the footprint itself, but there will be enhancement effects in the area surrounding the closed area. The potential benefits of OWF footprint closure to simply allow restoration of indigenous biological communities, thereby improving ecosystem health and resilience, also needs to be evaluated. v Review of the reef effects of offshore wind farm structures and potential for enhancement and mitigation Data gaps and questions to inform a forward research programme identified in this study include the future direction of OWF design/operation, fisheries management issues in relation to OWFs, potential use of OWFs as feeding and nursery areas for fish, birds and other mobile species, impacts of OWFs and associated reefs with regard to invasive species. A range of questions in relation to the potential for enhancing/exploiting natural populations of crustacea/bivalves or algae, (as opposed to developing aquaculture methods and technologies appropriate for deployment within the OWF footprint), has also been identified. The following paragraphs summarise the main conclusions of this report: (1) Turbine towers and their associated scour protection constitute surfaces readily colonised by a typical and broadly predictable assemblage of organisms, reflecting zonation patterns observed in adjacent intertidal and sub-tidal rocky shore communities. The physical impact and biological impact of OWFs will be proportional to the level (area/extent) of scour protection utilised and this will need to be assessed on a site specific basis. Site dependent factors such as proximity to rocky shores and hydrographic conditions influence the presence of some species and the absence of others at specific OWF sites. The structures may also extend the distributions of some mobile species such