Spatio-temporal Changes in Beluga Whale, Delphinapterus leucas, Distribution: Results from Aerial Surveys (1977-2014), Opportunistic Sightings (1975-2014), and Satellite Tagging (1999-2003) in Cook Inlet, Alaska

Cook Inlet is inhabited year-round by a small, distinct group of beluga whales, Delphinapterus leucas. This endangered and declining population near Anchorage lives in waterways frequented by fishing fleets, container ships, oil-gas development, air traffic, and military operations. Their summer distribution has been well-studied but in winter and early spring the combination of poor sighting conditions (low light levels, white whales among ice floes) and whale behavior (close association with ice, longer, deeper diving patterns, smaller groups) make detection difficult.

Based on our review of beluga presence data from aerial surveys, satellite-tagging, and opportunistic sightings, their range has contracted remarkably since the 1990’s. Almost the entire population is found in only northern waters from late spring through the summer and into the fall. This differs markedly from surveys in the 1970’s when whales were found in the lower inlet by midsummer.

By early June, belugas now gather at river mouths in the Susitna Delta and Chickaloon Bay. Since the Endangered Species Act listing decision in 2008, 83% of the total population now occupies the Susitna Delta in early June compared to roughly 50% in the past. In August, sightings increase in Knik Arm, with some dispersal to deeper upper inlet waters. In fall, belugas disperse south, though few whales are found in the lower inlet. In winter, belugas now occur in the upper inlet and make occasional visits to the lower inlet, with no evidence of migration out of Cook Inlet. The population appears to now be consolidated into preferred habitat in the upper-most reaches of Cook Inlet.