Range contraction in a beluga whale population

Abstract

The small, isolated population of beluga whales Delphinapterus leucas in Cook Inlet, Alaska, USA, has had a distinct contraction in range over the past 3 decades. This contraction is a function of a decline in abundance, evidently caused, at least in part, by high takes during unregu- lated subsistence hunting. During the 1990s, hunting resulted in takes of over 50 whales yr -1 , all of which occurred in the northern portion of Cook Inlet. Concurrent with the decline in abundance, sightings became rare in the southern inlet, even though human impact had been relatively low there. Curiously, the density of whales in the northern inlet remained high in spite of the hunts. Sig- nificant changes in beluga whale distribution are evident across 3 periods: 1978-1979 (the earliest well-documented data); 1993-1997 (during the recorded decline in abundance); and 1998-2008 (when hunting was regulated and recovery was anticipated). The center of the summer range of bel- uga whales contracted northeastward into upper Cook Inlet from the 1970s to the 1990s (38 km; p = 0.042) and continued into the 2000s (total of 53 km; p = 0.022) with a longitudinal shift east towards Anchorage (the largest city and port in Alaska) occurring between the 1990s and 2000s (17 km; p = 0.025). The result is a reduced range (>7000 to <3000 km 2 ) in all but the area with the highest degree of human disturbance. If and when the Cook Inlet beluga whale population begins to increase, a reoccupation of peripheral habitats may be the first indication of recovery.