Seabird feeding on benthic amphipods facilitated by gray whale activity in the northern Bering Sea

Abstract

Ampeliscid amphipods are the dominant benthic fauna in the N Bering Sea and the major food of the California gray whale Eschrichtius robustus. Benthic amphipods brought to the surface during gray whale feeding provide a food source for surface-feeding birds as well as diving birds. Infaunal amphipods are abundant at the surface in whale slicks, and abundance and size-class of these floating amphipods directly reflect relative abundance and size-class of the major amphipod species found in the underlying benthos. Surface-feeding birds ate mostly small amphipods at slicks, which were the dominant amphipod size-class observed in the tows. Birds as divergent in size as northern fulmars Fulmarus glacialis (700 g) and red phalaropes Phalaropus fulicaria (60 g) consumed small amphipods or fragments < 2 mm in length. Thick-billed murres Uria lomvia, which dive to feed, caught the larger amphipods that sank. Location and abundance of northern fulmars and red phalaropes feeding in the study area were positively related to occurrence of feeding whales. The breeding thick-billed murres and black-legged kittiwakes Eschrichtius robustus were in a more restricted distribution on the east side of the grid, nearest the seabird colonies on King Island, Alaska. The local distribution of all four species is shaped by whale feeding activity, and their diet is a direct reflection of benthic population structure. -from Authors