Rare detections of North Pacific right whales in the Gulf of Alaska, with observations of their potential prey

Abstract

The North Pacific right whale Eubalaena japonica was heavily exploited throughout the Gulf of Alaska by both historical whaling and 1960s illegal Soviet catches. It is now extremely rare in this region (2 sightings between 1966 and 2003 and passive acoustic detections on 6 days out of 80 months of recordings at 7 locations). From 2004 to 2006, 4 sightings of right whales occurred in the Barnabus Trough region on Albatross Bank, south of Kodiak Island, Alaska, USA. Sightings of right whales occurred at locations within the trough with the highest density of zooplankton, as measured by active acoustic backscatter. Net trawls through a high-density demersal layer (~150 to 175 m) revealed large numbers of euphausiids and oil-rich C5-stage copepods. Photo-identification and genotyping of 2 whales failed to reveal a match to Bering Sea right whales. Fecal hormone metabo- lite analysis from 1 whale estimated levels consistent with an immature male, indicating either recent reproduction in the Gulf of Alaska or movements between the Bering Sea and the Gulf of Alaska. Large numbers of historic catches of right whales occurred in pelagic waters of the Gulf of Alaska, but there have been few recent detections in deep water. Given that there is no other location in the Gulf of Alaska where right whales have been repeatedly seen post-exploitation, the Barnabus Trough/Albatross Bank area represents important habitat for the relict population of North Pacific right whales in the Gulf of Alaska, and a portion of this area was designated as critical habitat under the US Endangered Species Act in 2006.