Seasonal distribution of short-tailed shearwaters and their prey in the Bering and Chukchi Seas

Abstract

Short-tailed shearwater Puffinus tenuirostris is one the of abundant marine top predators in the Pacific; this seabird spend its non-breeding period in the northern North Pacific during May-September and many visit the southern Chukchi Sea in July-September. We examined factors affecting this seasonal pattern of distribution by counting short-tailed shearwaters from boats. Their main prey, krill was sampled by NORPAC net in the southeastern Bering Sea/Aleutian Islands and in the Bering Strait/southern Chukchi Sea. Short-tailed shearwaters mainly distributed in the southeastern Bering Sea/Aleutian Islands (60 ± 473 birds km-2) in summer (July) but in the Bering Strait/southern Chukchi Sea (19 ± 91 birds km-2) in fall (September). In the Bering Strait/southern Chukchi Sea size of krill was greater in fall (9.6 ± 5.0 mm in total length) than in summer (1.9 ± 1.2 mm). Within the Bering Strait/southern Chukchi Sea in fall, short-tailed shearwaters occurred more frequently in cells (50 km × 50 km) where large krill was more abundant. Our results suggest that the seasonal northward movement of short-tailed shearwaters could be associated with the seasonal increase of large krill in the Bering Strait/southern Chukchi Sea. This study substantiates the importance of krill, which is advected from the Pacific, as a prey of top predators in the Arctic marine ecosystem.