Windfarms, fishing and benthic recovery: Overlaps, risks and opportunities

Abstract

The UK is a leading nation in the development of large offshore wind energy installations (OWFs). Since 2000, the UK has installed 2610 turbines covering over 2000 km² of UK seas. As these sites overlap with historic fishing grounds as well as Marine Protected Areas it is important to understand the relationship between the presence of these OWFs and fishing activity to assess the extent to which OWFs could act as de facto MPAs with respect to fisheries management, providing other environmental impacts are mitigated. We assessed the extent to which the fishing activity of vessels using bottom-contacting mobile gears (trawls, dredges and demersal seines) were impacted by the construction of 12 offshore windfarms in the UK EEZ. Using publicly available Global Fishing Watch fishing effort data, we found fishing rate from vessels using bottom-towed gear was reduced by 77 % following OWF construction in 11 of the 12 sites studied. A decline in bottom-towed fishing activity was recorded in OWFs where turbines were constructed in a densely aggregated patch, and an increase in fishing activity where turbines were positioned as several distinct aggregated patches within the site. We conclude that bottom-towed fishing activity is affected by turbine layout, with OWFs likely offering some protection to the benthic environment from bottom-towed gear. We suggest this reduction in bottom-towed fishing provides space for co-location opportunities and note that consultations on domestic MPA designations should involve offshore wind stakeholders in terms of OWF ‘co-location’ with and ‘avoidance’ of MPAs.

Introduction

Offshore wind energy generation offers a vital route to decarbonising the UK’s energy supply. Plans are in place in adjacent EU waters to develop 450 GW of energy from renewables by 2050 to meet carbon-neutral targets [1]. The UK Government are calling to increase supply from 10.5 GW to 40 GW by 2030 [2], [3]. This 4-fold increase in the amount of power generated by windfarms offshore in order to meet current targets would potentially lead to greater areas of sea being compromised with respect to traditional industrial activity such as fishing – particularly in areas such as the North Sea [4], [5], [6] – raising concerns that displacement of fishing activity will further increase pressure on the seabed outside offshore windfarms (OWFs) [7], [8]. However, the removal of bottom towed fishing pressures from within the UK’s current and planned OWF boundaries could offer protection to some 21,000 km² of – albeit altered – seabed¹ [4], [5] outside the UK’s current Marine Protected Area (MPA) network.

Selecting conservation measures to reduce or ban fishing has historically been complex in offshore EU waters [9], and relies on a ‘Joint Recommendation’ process whereby fishing states must agree to the conservation measures outlined by the host member state of any MPA. However, the Marine Strategy Framework Directive (MSFD) process has urged ICES to provide advice to member states over the potential to ‘trade-off’ fishing vs achievement of ‘seafloor integrity’ at a macro-scale [10]. These developments all point to the potential to close significant areas of seafloor to bottom trawls that go beyond MPA boundaries for wider societal goals (e.g. Davies et al. [11]).

Offshore fishing in UK seas has tended to be fairly consistent in location since at least 2015 with fishers generally targeting ‘core’ areas at greater effort than less productive areas [10], [12], [13], [14]. The presence of windfarm infrastructure and any resulting reduction in fishing pressure from vessels using bottom-towed gear has potential benefits for the marine ecosystem [15]. The cabling, turbine monopiles and surrounding rock armour change habitat dynamics from sedimentary to reef-like (or artificial reef) structures rich in bivalves, corals, bryozoa and hydroids [16], [17], [18], [19]. The shift to these organisms provides a suspension feeding capacity (filtration by bivalves) in an otherwise depositional and ‘scavenging’ environment where flat sand and coarse gravel dominate (e.g. submerged worms, low biomass of invertebrate epifauna per unit area) [20]. However, studies show this could come at a cost with abundance of a range of soft-bottom species declining, including dab (Limanda limanda), weaver fish (Echiichthys vipera) [21], and potentially lesser sandeels; an important forage fish for seabirds and marine mammals [22].

Such modification of ‘sedimentary’ habitat in natural ‘sandbank’ Special Areas of Conservation (under the UK Habitats Regulations), or ‘circalittoral sand/mixed sediment’ features in Marine Conservation Zones is controversial [15]. UK conservation advisors have assessed the impacts of shifts in habitat-type as to whether they significantly alter the ecological character of entire offshore MPAs that may require mitigation – for example to mitigate the change from sedimentary to rocky in physical and ecological characteristics [16]. The interactions between MPAs and windfarms has affected construction aspects such as cable routing around MCZs (e.g. Cromer Shoal Chalk Beds MCZ) [23]. That being the case, windfarms, the ecological communities they attract [17], [24], and the effective restriction to bottom towed fishing gear brought about by safety issues could enable them to be considered as Other Environmental Conservation Measures (OECMs) [25]. That is providing any short- and/or long-term negative impacts on marine mammals, seabirds and other wide-ranging species are mitigated [26], [27], [28].

The socio-economic benefits resulting from the removal of fishing pressures from OWFs could also mimic those offered by MPAs. Spill-over of commercially important fish species (e.g. cod (Gadus morhua), sole (Solea solea), whiting (Merlangus merlangus) [21], [29]), found to become more diverse and abundant within the arrays, provides opportunities for improved fishing outside the OWF sites, with vessels benefiting from a ‘reserve effect’ [11], [30]. Furthermore, the OWFs themselves could present ample opportunity for co-location with a range of other marine activities if integrated via effective marine spatial planning [6], [8]. Reduced-impact passive gear use (e.g. potting for crabs [31], [32]), restoration of historic native oyster (Ostrea edulis) reefs [33], [34] and sustainable mariculture (e.g. seaweed cultivation) [35] are but a few examples. Such activities especially strengthen the provisioning and regulating ‘ecosystem services’ provided by each OWF; improving fisheries, carbon sequestration, and water quality [36], [37].

Whilst some nations (e.g. Denmark and the Netherlands) have outright bans on seabed trawling in windfarms [38], this is not the case in the UK. Nevertheless, fishing effort has been reported as being reduced around operational windfarms because of the risks of bottom-towed gear being snagged, and ship strike with monopiles [39], but quantification of this effect has been limited in the literature.

This study examines the extent to which the construction of offshore windfarms impacts fishing effort of vessels using bottom-towed gear (bottom trawls, dredges and demersal seines). We identify the risks and barriers OWF construction pose to fishing activity and explore the opportunities this presents for benthic protection and recovery.