Tidal streams provide important foraging habitat for several species of marine top predator. This habitat is potentially vulnerable to alteration from the construction of tidal stream turbines. These turbines have been installed in the north of Scotland, with several hundred more planned. Tidal turbines may affect inshore habitat or prey distribution by shifting tidal flow patterns, altering benthic composition or by forming reefs. However, different species will be affected to varying extents based upon their ecological niche. The black guillemot Cepphus grylle, an inshore, diving seabird known for benthic foraging has been identified as a species vulnerable to tidal turbines due to its use of tidal streams. Additionally, the species has been designated as a feature of six Marine Protected Areas (MPAs) across Scotland. Both of these developments highlighted gaps in our knowledge of black guillemot foraging ecology, and the need to address the extent tidal stream turbines may affect, and MPAs will protect, black guillemots. The aim of this thesis is to investigate these knowledge gaps relating to black guillemot foraging ecology, with a particular focus on tidal stream use.
I related GPS tracking data to predictive habitat data and tidal models to investigate the foraging ecology of black guillemots at three colonies in Caithness and Orkney. Firstly, I addressed the overlap between foraging locations and the MeyGen tidal lease area within the Inner Sound of the Pentland Firth. I found 9.5% of foraging locations overlapped with the lease area. Individuals mostly foraged parallel to the MeyGen area, associating with slower velocities and shallower depths than those occurring within the lease area. Tidal streams were found to be one of multiple foraging niches. These included relatively shallow (14m) kelp-dominated habitats, and habitats related to sand substrate with dense infaunal communities (20m). Use of these niches was dependent on colony specific availability, and surrounding depth profiles. Within these niches, individuals partitioned their foraging locations, and exhibited strong site fidelity. Some individuals displayed fidelity to tidal streams near the colony, while others travelled further (maximum 25 km) to alternative habitats not associated with tidal currents. The implications of different behaviours on chick provisioning and growth were investigated. I found diet to vary among nests, being either composed of: frequent feeds of diverse prey; or in-frequent feeds, of energy rich prey. These provisioning strategies did not influence chick growth. Varied foraging strategies are potentially driven by differing energetic benefits. I compared camera traps and visual observations as study techniques of chick diet and nest predation. Using these methods, additional sources of colony failure were identified, including adverse weather, and predators (both avian and terrestrial), which should be taken into account in surveys of nest success. Using ring recovery data, I investigated natal dispersal and philopatry across Britain and Ireland, as metapopulation dynamics may have implications for colony recovery. These properties were found to vary with latitude, potentially related to regional environmental conditions.
In relation to MPAs, the findings of this thesis have implications with regards to the habitats associated with foraging, and the distance birds will travel to use them. Regarding tidal turbines, most black guillemots did not forage in areas currently suitable for tidal stream turbine deployment, but narrow characteristics of depth and velocity were used by foraging individuals within tidal streams. Therefore, minor changes to environmental conditions caused by turbines may have large impacts for the birds that do specialise in foraging in areas of high tidal flow.
This thesis may be available by request from the author or university.