EU request on economic, social, and ecological impacts of offshore wind farms (OWFs) and floating offshore wind farms (FLOWs) on fisheries in the Baltic Sea, Celtic Seas, and Greater North Sea

This advice addresses aspects of the economic, social, ecological, and cumulative impacts of offshore wind farms (OWFs) and floating offshore wind farms (FLOWs). It focuses on the scope of the existing evidence base, data, and methods to assess impacts, and it considers marine spatial planning (MSP) and technical measures as approaches for mitigating unwanted impacts.

Systematic review of available studies identified OWF and FLOW impacts on income, fishing grounds, catch opportunities and operating costs in EU Member States. For all types of impacts, there were more studies reporting on negative impacts on fisheries than studies reporting on positive impacts. Observed impacts were dependent on context factors such as the type of wind farm, development phase of the wind farm (pre-construction, construction, operation, or decommissioning), and adaptive capacity of fishers. ICES did not identify any studies of trade-offs between the economic impacts of fisheries and wind farms.

ICES identifies five classes of data that are required for assessments of the economic and social impacts of wind farms on fisheries: vessel positional data, fisheries catch and effort data, fisheries economic data, fisheries social data and OWF and FLOW data. Existing available data are mostly not collected or collated at sufficiently high resolution, and cannot yet be linked in ways, that enable full evaluation of direct or indirect economic and social impacts of wind farms.

Some pressures associated with the phases of OWF and FLOW development have known or predicted local impacts on commercially fished species. A trait-based analysis was applied to estimate the local vulnerability of commercially fished species to the operational phase of OWF development in the Baltic Sea, Celtic Seas, and Greater North Sea ecoregions. Sediment resuspension was the most impactful pressure. ICES, however, did not identify any population‑level (stock-level) assessments of impacts on commercially fished species. Requirements for population-level assessments that account for wind farm impacts across the distributional range of populations are described.

ICES did not locate sufficient evidence to directly assess the effects of existing wind farms on the western Baltic herring. There was no direct evidence of wind farm effects on the critically endangered Baltic Proper harbour porpoise. However, information on the responses of other harbour porpoise populations to pressures associated with OWFs or FLOWs, especially noise, is sufficient to conclude that wind farm developments in the Baltic Proper harbour porpoise core distribution area would lead to pressures that pose a risk of further population decline.

Wind turbines create atmospheric wakes, and their underwater structures modify currents and stratification. Atmospheric wakes reduce mixing of the water column on large scales, and underwater structures increase mixing on smaller scales. Especially in seasonally stratified areas, wakes reduce primary production, while underwater structures increase it. Underwater structures also support communities of filter feeders that consume additional primary production.

OWFs and FLOWs introduce artificial hard substrates and modify distributions of indigenous and non-indigenous species, especially in areas dominated by soft sediments and away from rocky coasts and seabeds. The magnitude of their impact in relation to other artificial hard substrates is not known. Based on the observed colonization of other floating structures, the transport of FLOW turbines between ports and wind farms may facilitate the spread of non-indigenous species.

Dynamic cables associated with FLOW may affect pelagic species because of direct energy emissions, physical effects, and/or indirect ecological effects. However, ICES identified no studies of the effects of dynamic cables. Effects were inferred from studies of other subsea power cables, that all reported local rather than population-level effects.

ICES evaluated existing methods and models with potential to assess the cumulative impacts of OWFs and FLOWs. Some were deemed either suitable (subject to evidence and data for parameterization), or to have potential through further development, to quantify cumulative impacts, and to test how these impacts could be modified by mitigation options. Cumulative assessments would be facilitated by higher resolution economic, social, and ecological data, including information on the locations and developmental phases of wind farms at ecoregion scales.

Mitigation is intended to reduce or compensate for adverse economic, social, and ecological impacts of OWFs and FLOWs. MSP and subordinate planning processes, instruments, and supporting procedures contribute to the identification and implementation of mitigation options. Multiuse and co-use approaches provide mitigation by enabling coexistence between users and activities. Technical mitigation options, such as the positioning of cables and noise abatement, modify aspects of wind farm design to improve options for the operability of fishing vessels within and around wind farms and to reduce adverse ecological impacts. These mitigation options facilitate MSP solutions but are usually enabled by sectoral policies. Mitigation through compensation provides substitute resources or environments. Stakeholder involvement, engagement and co-design help to enable development of mitigation options that are technically, economically, politically, socially, and ecologically feasible and that are supported, or at least accepted, by stakeholders.