Abstract
This technical note has been prepared by Environmental Resources Management Ltd (ERM) for the Offshore Wind Industry Council (OWIC) led Offshore Wind Evidence and Change (OWEC) Strategic Compensation Studies (SCS) project. The aim is to provide an up-to-date overview of red -throated diver Gavia stellata (RTD) compensation measures and opportunities for improving ecological outcomes which could be applied by the offshore wind farm (OWF) sector.
RTD is the most common diver species in the UK, with breeding populations present in Scotland and overwintering (non-breeding) populations in more southern regions on the east and west coasts. The focus here is on overwintering populations, which are known to also include some individuals using sites as ‘lay-overs’ during migration, in English and Welsh waters: specifically those which are classified under the EU Birds Directive, and which are qualifying features of designated Special Protection Areas (SPAs) (see Table 1, Section 2).
Over the winter period (generally the beginning of November to the end of March), RTD make use of large inshore bays and the outer extents of estuaries (O’Brien et al., 2008; Guse et al., 2009; Skov et al., 2016). In these habitats individuals spend several months on the water, feeding on a variety of prey resources (Guse et al., 2009). At the end of the winter period (during February and March) individuals form aggregations on the sea surface before leaving over a short number of days for the spring migration back to breeding grounds in northern Scotland, Scandinavia, Iceland, and Russia (Duckworth et al., 2022; Kleinschmidt et al., 2022).
Populations are subject to a number of threats, both from anthropogenic activity and natural/environmental changes. Disturbance/displacement due to infrastructure and marine activity is considered to constitute the key threat to wintering RTD. Other threats may include loss or alteration of supporting habitat and prey species; barrier effect and collision with infrastructure during migration; bycatch in fisheries; and natural threats such as bird flu and climate change.
The RTD knowledgebase is expanding, regarding abundance and distribution, with recent and ongoing surveys of SPA populations (e.g. the Outer Thames Estuary in 2018, and the Greater Wash due to be published in 2025). In addition, observations and monitoring are progressing regarding responses to infrastructure projects and vessel activities (APEM, 2016; Burger et al., 2019; Allen et al., 2020), and the effects of displacement on individuals (e.g. Thompson et al., 2023).
There is a need to review, understand, and potentially offset displacement of RTD from wintering habitats. This is predominantly due to increasing infrastructure developments, and associated vessel activity, such as recent and proposed OWF projects in the North Sea (e.g. East Anglia ONE North and East Anglia TWO (EA1N and EA2) and North Falls) and in the Irish Sea (e.g. Morecambe OWF).
This note aims to provide an overview of the current status of key wintering RTD populations, and place this in perspective with reference to OWF projects, and potential compensatory measures.