Individual variation in movements of satellitetracked humpback whales Megaptera novaeangliae in the Eastern Aleutian Islands and Bering Sea

Abstract

Humpback whales utilize waters off the Aleutian Islands and Bering Sea as foraging grounds during summer months. Currently, the fine-scale movements of humpback whales within these feeding grounds are poorly understood. In the summers of 2007 to 2011, 8 humpback whales were tracked with satellite tags deployed near Unalaska Bay. Individuals were tracked for an average of 28 d (range = 8-67 d). Three whales remained within 50 km of their tagging locations for approximately 14 d, while 2 others explored areas near the northern shore of Unalaska Bay and Unimak Pass. Two whales moved west: one traveled to the Island of Four Mountains and returned to the northern side of Umnak Island, while the other moved through Umnak Pass and explored feeding areas on both sides of Umnak Island. Remarkably, 1 individual left Unalaska Bay soon after tagging and moved ~1500 km (in 12 d) along the outer Bering Sea shelf to the southern Chukotka Peninsula, Russia, then east across the Bering Sea basin to Navarin Canyon, where it remained until transmissions ceased. Most area-restricted search (i.e. foraging) was limited to waters shallower than 1000 m, while movement into deeper water was often associated with travel behavior. Tagged animals spent more time on the Bering Sea shelf and slope than the North Pacific. Movement patterns show individual variation, but are likely influenced by seasonal productivity. This study provides evidence that although humpbacks aggregate in well-known foraging areas, individuals may perform remarkably long trips during the feeding season.