Seasonal movements and foraging behaviour of northern resident killer whales (Orcinus orca) in relation to the inshore distribution of salmon (Oncorhynchusspp.) in British Columbia

Abstract

The hypothesis that northern resident killer whales (Orcinus orca) move in response to the seasonal availability of salmon (Oncorhynchus spp.) was tested using sightings and acoustic recordings of whales and data on the timing and abundance of salmon in Johnstone Strait, off Vancouver Island, between 1984 and 1988, and from King Island, on the central British Columbia coast, for a 2-month period in 1989. Whales were most abundant in Johnstone Strait between July and October when salmon migrate through the strait. Individual whales seen in the strait during summer were observed around King Island in spring 1989, coinciding with local sockeye and chinook salmon runs. In Johnstone Strait during summer 1988, whales foraged along the shore and in areas of strong current, where salmon occur in high densities. However, less than half of the 16 pods in the northern resident community were present on more than 15% of summer days (1984–1988). The occurrence of 6 pods (A1, A4, A5, C1, D1, and H1) in Johnstone Strait during summer was positively and significantly associated with sockeye and pink salmon abundance, whereas pod G1 was positively and significantly associated with chum salmon. Although we demonstrate an association between certain pods and certain salmon species, we cannot determine whether this reflects the true preference of pods or represents differences in the whales' arrival times in Johnstone Strait that are related to other factors. Our data suggest that within the northern resident community, pods may have seasonal ranges.