The importance of the “Polar Front” as a foraging habitat for guillemots Uria spp. breeding at Bjørnøya, Barents Sea

There are large breeding colonies of common guillemots Uria aalge and Brünnichʹs guillemots Uria lomvia at Bjørnøya in the Barents Sea. We studied the foraging ecology of these guillemot populations during the breeding season by ship surveys off the island. The guillemots foraged in all directions from the island, but the main aggregations of foraging birds were encountered south of Bjørnøya. Common guillemots tended to forage mainly on the southern side of the island. Most of the foraging aggregations were encountered 25–60 km from the island. These guillemot aggregations were located at the surface expression of the “Polar Front” and in the strongly stratified water on the offshore side of the front. The position of the surface “Polar Front”, which roughly follows the 100 m isobath, seems to be relatively predictable and is probably dependent on bathymetry and strong tidal currents. The euphausiid Thysanoessa inermis predominated in the diet of adult Brünnichʹs guillemots collected during the study, whereas fish were brought back to their young. Capelin Mallotus villosus is an important prey for guillemots in the Barents Sea, but in years when capelin is scarce in the region, guillemots may rely more on euphausiids for subsistence.