KILLER WHALE (ORCINUS ORCA) DISTRIBUTION AND ABUNDANCE IN THE CENTRAL AND SOUTHEASTERN BERING SEA, JULY 1999 AND JUNE 2000

Predation by killer whales (Orcinus orca) has been advanced as a factor in the decline of two marine mammals in Alaskan waters: the sea otter (Enhydra lutris) and the Steller sea lion (Eumetopias jubatus). Estes et al. (1998) implicated killer whale predation as the likely cause for the recent decline of the sea otter population in the Aleutian Islands, due, in part, to the lack of observations of killer whale predation on sea otters in the 1980s contrasted with recent observations. An investigation of the possibility that killer whales were responsible for the decline in Steller sea lions in Alaska concluded that killer whale predation probably did not cause the decline, but now that the sea lion population is relatively small, killer whale predation may be a contributing factor to further decline. Our objective was to estimate the abundance of killer whales in the Bering Sea as a first step in evaluating these predation hypotheses.