Regional diving behavior of Pacific Arctic beluga whales Delphinapterus leucas and possible associations with prey

Abstract

Two populations of beluga whales Delphinapterus leucas in the Pacific Arctic make seasonal migrations to regions characterized by diverse bathymetry and hydrography, yet there is limited information contrasting behavior and foraging across regions. We used satellite-linked timedepth recorders attached to 30 belugas from 1997 to 2012 to infer the depths at which belu- gas forage seasonally and regionally. We also examined the correspondence between patterns of beluga diving and the vertical distribution of a primary prey species, Arctic cod Boreogadus saida, within the western Beaufort Sea. A suite of regional diving metrics revealed that beluga dive behavior varied among regions and sometimes between populations. Estimates of occupancy time at depth, in addition to maximum and modal dive depths for 6 h periods, suggested that Eastern Chukchi Sea and Beaufort Sea belugas were regularly diving to the seafloor in shallow shelf regions. Along slope margins and in the deep Canada Basin (>3000 m), specific portions of the water column were more frequently targeted. The greatest maximum daily dive depths were >900 m in the Canada Basin. Arctic cod were most abundant at 200�300 m in the western Beaufort Sea, and beluga dives within the survey area also most frequently targeted these depths. These results are consistent with a hypothesis that Arctic cod are a primary prey item for Pacific Arctic belugas and suggest that foraging belugas dive to depths that maximize prey encounters. In the context of a rapidly transforming Arctic ecosystem increasingly exposed to anthropogenic activi- ties, our results quantify the ecological importance of key regions for these 2 populations.