Elasmobranchs in offshore wind farms

The development of offshore wind farms (OWFs) in coastal seas presents both risks and opportunities for threatened elasmobranch populations, but their actual influence on elasmobranch presence and habitat use remains unclear. As more OWFs are planned, the lack of available space puts pressure on stakeholders to create multi-use areas as demands from fisheries, conservation and the energy sector become increasingly overlapping. Insight into interactions between these demands is needed to support policymakers in marine spatial planning and management decisions. One of the important questions is to what extent OWFs influence elasmobranch presence and habitat use. Here, we (i) ascertain elasmobranch occurrence in OWFs, (ii) determine whether elasmobranch presence varies between sampling locations, and (iii) investigate the influence of seasonality on elasmobranch presence. We collected 436 seawater samples within four OWFs and the presence of 5 different elasmobranch species (2 sharks, 3 skates) was confirmed. The overall detection probability of elasmobranchs in the four OWFs was 8.5 %. A quarterly sampling campaign over 2 years demonstrated the seasonality of Mustelus asterias on the subsea power cables, which corresponded with known migratory movements of this species. Our findings confirm that sharks and skates are present in OWFs. We advise caution when introducing multi-use activities that could counteract the benefits of bottom trawling fisheries exclusion. Investigating how these threatened species use OWFs would aid policymakers in determining the (multi-use) function of OWFs in terms of EU legislative acts including the Habitat Directive, MSFD, Biodiversity Strategy 2030 and the Nature Restoration Law. • Five elasmobranch species were detected in OWFs across different seasons using eDNA. • Elasmobranchs use OWFs as a habitat, understanding habitat use needs further study. • Detections of the rare C. maximus support variable winter migration patterns. • M. asterias was detected more often on export subsea power cables than within OWFs. • OWFs don't block seasonal migration, but subtle EMF effects need further study.