Seabird Aggregation around Vessels during the Winter Trawl Fishery for Walleye Pollock in the Sea of Okhotsk

Abstract

The observations conducted during the Walleye Pollock expedition to the Sea of Okhotsk in January–April 2015 showed that various seabird species (at least 12) aggregate permanently around trawlers in the Sea of Okhotsk. The birds are attracted by fish-processing waste. The quantitative and species composition of aggregations is dynamic. The richest of these in terms of number of species and the most abundant (up to 23 000 individuals around one vessel at a time) are formed in the Kamchatka–Kuril subzone, where numerous overwintering birds arrive from adjacent ocean waters. The Northern Fulmar accounts for a major part of the aggregation (68.9% of all birds); this bird dominates most of the fishery areas. The second most-abundant group of species is large white-headed gulls of the genus Larus (31.0%), mainly the Slaty-backed Gull. In general, the pollock trawl fishery is regarded as an influential factor that causes large overwintering grounds of seabirds to form in the Sea of Okhotsk. Fish-processing waste disposed overboard supports a huge bird community by providing a stable food supply during the harsh season.