Comparative Distribution, Movements and Diet of Harbour and Grey Seals from Moray Firth, N. E. Scotland

Abstract

The distribution, movements and foraging activity of harbour and grey seals from the inner Moray Firth, N.E. Scotland, were compared using a combination of observations at haul-out sites, VHF and satellite-link telemetry, and analyses of diet composition. Terrestrial abundance of both grey and harbour seals was highest during the summer but there were marked differences in the extent to which the two species moved between different haul-out sites. Harbour seals showed local seasonal changes in distribution, but all 21 radio-tagged seals moved only to alternative haul-out sites within a range of 75 km. In contrast, four of the five grey seals tracked from the Moray Firth moved to haul-out sites 125-365km away, and provided evidence of interchange between the Moray Firth and other grey seal breeding areas in Orkney, the Firth of Forth and the Farne Islands. All harbour seals foraged within 60 km of their haul-out sites, but showed seasonal variation in their foraging areas which was related to changes in their terrestrial distribution. In contrast, those grey seals which foraged within the Moray Firth travelled up to 145 km from haul-out sites. Nevertheless, there was some overlap in the foraging areas used by harbour seals and grey seals in more inshore areas. Sandeels, gadoids, flatfish and cephalopods formed over 95% of the diet of both species. However, dietary data, particularly for grey seals, may be biased toward those individuals which fed in more inshore areas. These results suggest that Moray Firth harbour seals can be considered as a relatively discrete population, with clear links between breeding, feeding and resting areas, and little exchange of adults between this and adjacent breeding areas in Orkney and the Tay Estuary. In contrast, grey seals from several different breeding sites appear to move into the Moray Firth in summer and use the area primarily for foraging and non-breeding haul-out.