BRANTA — Nicholas J. Goldsmith
Quantifying seabird habitat use and occurrence across tidal-stream environments in Anglesey, UK
Institution: Bangor University
Supervisors: James Waggitt
Details: MSc, 2017
Subject Keywords: seabirds, renewable energy, tidal stream, current, Anglesey, habitat use, behaviour, modelling
Species Keywords: Auk, Razorbill, Common Guillemot, Northern Gannet, gulls, Herring Gull, Black-headed Gull, European Shag, Great Cormorant, Common Gull, Great Black-backed Gull, Lesser Black-backed Gull
Tidal stream environments are highly dynamic but predictable areas of the ocean. This means that multiple species of seabird utilise these environments to forage due to the increased prey vulnerability caused by the hydrodynamics of the area. Tidal stream environments also have an untapped potential for marine renewable energy (MRE) extraction via tidal stream turbines. These turbines could pose a direct threat from species that are foraging in these areas. To identify the potential threats understanding of the habitat use of seabirds at these sites is needed. This study provided this information for seven sites along the north coast of Anglesey, Wales. Alongside the direct habitat use observations TELEMAC-2D modelling and multibeam sonar allowed the environmental characteristics to be quantified per site. This combination of observations, tidal state analysis and environmental variables allowed an in depth understanding of the drivers of seabird habitat use. Tidal state explained a large amount of the variation in observed patterns for the species groups encountered in the largest numbers (large auks and small gulls) but the environmental variables explained greater variation for the groups observed in fewer numbers. Point Lynas and Moelfre throughout all seasons maintained large populations of multiple species, suggesting these areas are good year round foraging areas. The environmental variables which were associated with these sites were an intermediate current speed, average depth (~20 m) and large depth variation (seabed roughness). These three variables were the main drivers for all species groups at all sites. All species showed a negative relationship with increasing current speed, but a positive relationship with increasing depth variation. This suggests most species have a preference to slow moving currents but at sites with increased bathymetric complexity. These results suggest that placing MRE devices in fast flowing deep waters on smooth seafloors will likely cause the least impact to the seabird populations. This research provides the first site specific habitat use study and will act as a baseline for subsequent studies around Anglesey.