Abstract
The global shift toward renewable energy has accelerated the development of offshore wind farms (OWFs) as a key source of sustainable energy. However, this expansion often targets relatively undisturbed areas, introducing new anthropogenic impacts to marine habitats and species. In Europe, the shallow waters of the North Sea provide an ideal setting for the installation of OWFs, making the region a global hotspot for offshore wind energy. Between 2010 and 2021, 20 OWFs have been constructed in the German North Sea, and significant growth is legally stipulated for the coming years (WindSeeG, 2016).
With the increase in OWF installations, concerns have been raised about their environmental impacts, particularly on marine fauna. Many bird populations rely on the North Sea as permanent or migratory habitats, making them especially vulnerable to habitat alterations and disturbances caused by wind farms (Welcker and Nehls, 2016). Effective spatial planning and conservation measures require robust assessments of these impacts, yet limitations in methodologies and spatial analyses present significant challenges (Dierschke et al., 2016; Furness et al., 2013). Current environmental impact studies often lack the spatial resolution and methodological consistency over the necessary long-term period required to capture the full extent of the impact of offshore wind farms on marine populations.
In Germany, mandatory five-year post-construction monitoring programmes aim to assess OWF impacts, including monthly, large-scale digital aerial surveys around each wind farm to survey seabirds and marine mammals with standardised methods (BSH, 2013). Hence, extensive monitoring data are available around each wind farm. While recent studies have begun to address OWF effects at broader spatial and temporal scales (e.g., Garthe et al., 2023; Vilela et al., 2021), significant gaps remain in understanding the spatial extent and variability of impacts, particularly for vulnerable species like divers. Red-throated (Gavia stellata) and Black-throated divers (Gavia arctica), which are part of the North-west European wintering population, are highly susceptible to OWF disturbances (Heinänen et al., 2020; Mendel et al., 2019). These species migrate through the German Bight and are most abundant during the spring migration (Mendel et al., 2008), overlapping spatially and temporally with OWF development.
Protective measures, such as the designation of the Special Protection Area (SPA Eastern German Bight) within the European Natura 2000 network, have restricted OWF development near critical habitats (BMU, 2009). Covering 3135 km2, the SPA is surrounded by a defined main concentration area of 7000 km2, established in 2009, which includes six offshore wind farm areas. Within this area, the development of new offshore wind farms is currently on hold to safeguard the ecological integrity of the region (BMU, 2009).
However, the displacement of divers due to OWFs and associated activities, such as ship traffic, remains a key concern. Avoidance behaviour has been widely documented in divers and, more recently, in auks, with reported displacement distances ranging from 1.5 to 16 km across studies (Heinänen et al., 2020; Allen et al., 2020; Vilela et al., 2021; Garthe et al., 2023; Peschko et al., 2024). These estimates, often derived from monitoring programmes around single or multiple wind farms, show high variability and depend heavily on the methods, spatial coverage, and temporal scales used (Mendel et al., 2014; Petersen et al., 2014; Webb and Nehls, 2019). This variability suggests that displacement responses are context dependent and may differ among wind farms and regions, reinforcing the need for long-term, regional-scale studies that encompass multiple developments and assess cumulative effects.