| Summary: | Sightings and acoustic recordings from 1984 to 1989 of northern resident killer whales (Orcinus orca) from Johnstone Strait off north eastern Vancouver Island and from King Island on the central British Columbia coast were analysed to examine the hypothesis that northern resident whales move seasonally in their range to areas where salmon are available. Killer whales were most abundant in Johnstone Strait between July and October and infrequent during the remainder of the year. The increase in whale abundance during summer coincided with the migration of salmon (Oncorhynchus spp.) from offshore into Johnstone Strait. The occurrence near King Island in spring 1989 of the same resident whales that are seen in Johnstone Strait during summer, coincided with runs of sockeye and chinook salmon.
During July, August and September of 1984 through 1988, killer whale sightings were recorded virtually daily in the Johnstone Strait. Observations of killer whales in Johnstone Strait during the summer of 1988 showed that whales foraged along shore and in areas of strong current where salmon occur in high densities. Of the 16 killer whale pods in the northern resident community, however, less than half were present more than 15% of summer days (1984 to 1988). Regression results between numbers of whale days per week from each pod and numbers of salmon per week showed that the occurrence pods that were present on more than 15% of summer days in Johnstone Strait was positively and significantly associated with the abundance of sockeye and pink salmon (six pods). In addition to these, the occurrence of one pod that spent less than 15% of summer days in the Strait was positively and significantly associated with chum salmon.
Together these results support the hypothesis that northern resident killer whales select their habitat seasonally to feed on available salmon. The results also lead to the hypothesis that within the northern resident community each pod has a seasonal home ranges. === Land and Food Systems, Faculty of === Graduate
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