Investigating the foraging habitat of black guillemots in relation to tidal stream turbines

Abstract

**Abstract:** Tidal streams are a developing source of renewable energy and an important foraging habitat for several species of seabird. The north of Scotland is host to the world's first array of tidal stream turbines, constructed within the Inner Sound of the Pentland Firth. Inshore diving seabirds such as black guillemots Cepphus grylle are known to associate with tidal currents and dive to depths at which tidal turbines will operate. Black guillemots were therefore highlighted as vulnerable to foraging habitat alterations caused by turbine deployment and are at potential risk to collision with turbine blades. However, the extent to which these devices will affect black guillemots is unknown due to a lack of more detailed knowledge regarding their foraging ecology. This study addresses this knowledge gap by using GPS tracking technology to identify spatial and temporal aspects of foraging behaviour and habitat use. Thirteen adult black guillemots were GPS tracked during the 2016 and 2017 breeding seasons from Stroma, Caithness, an island of interest due to its close proximity to the MeyGen tidal lease area within the Inner Sound. Individuals displayed clear preference for specific foraging locations, associating strongly outside or within tidal streams. The foraging behaviour of individuals using the tidal stream was found to be associated with a narrow range of tidal velocities and depths. Foraging locations are potentially related to hydrodynamic features forming within these conditions, which are thought to aggregate prey. The MeyGen lease area generally contained faster tidal velocities and deeper depths than those associated with foraging, leading to minimal direct overlap. This research highlights the characteristics of tidal streams with which black guillemots associate. Such knowledge is vital when predicting the impact of tidal turbine installations on marine wildlife through environmental or habitat alteration. **Authors:** Daniel Johnston¹, Robert Furness², Alexandra Robbins³, Glen Tyler¹, Elizabeth Masden⁴ ¹British Trust for Ornithology, ²MacArthur Green Ltd, ³Scottish Natural Heritage, ⁴Environmental Research Institute