The Southern Resident Orcinus Orca Population in Puget Sound: Hypotheses on Population Ratios and the Effects of the Capture Era on Behavior of the Whales

This project set out to assess the population status of the southern resident community of Orcinus orca, the killer whale, in Puget Sound. The current number of whales in the community is 84, down from 97 in 1995, and it has been hypothesized that their numbers will continue to decline in the future. The study focused specifically on the residual effects of the capture era in the 1960’s and 1970’s that systematically cropped immature male and female killer whales from the southern resident community. Then, the behavioral adaptations that the killer whales appear to be making in response to their altered pod structures and dwindling numbers are evaluated. The two pods studied, J pod and K pod, are two of three pods in the southern resident community and were seen in close association with each other, particularly following the death of the last adult male in K pod, K1 in 1997. This whale was estimated to be 42 years old at death. Currently a large age gap exists in the K pod, with a total of only four males ranging in age from less than one year (born in 1999) to 13 years, and no adult males. Because of this age gap, the K pod members were observed swimming with the J pod whales more often. Although killer whales exist in a matriarchal society, it is believed that the males play an important role in the pod and entire resident community. It is thought that the observed association is due in large part to adult males in the pods playing a mentoring role for the younger whales. J pod in 1997 and 1998 had three adult males, which presumably were taking over the role of mentor for the juveniles in K pod, as well as perhaps mating with members of K pod to increase productivity within the pod. It appears that the changes in pod structure were brought on primarily by the capture operations in the 1960’s and 1970’s in the Puget Sound that took at least 34 killer whales from the southern resident community. Until the pod structures of the southern resident community can return to normal and the resulting age gaps are overcome, the altered behaviors we are seeing will continue. Although the effects of the capture era will probably be overcome eventually, other factors contributing to the declining southern resident killer whale population may complicate the whales’ ability to endure these residual capture era effects