Arguably the most cosmopolitan marine mammal species, killer whales are the top predators of the sea, capable of taking anything from small fish to blue whales. As much publicity as these charismatic carnivores get, it is remarkable that we don't know how many species there are. Most people don't know that killer whales inhabit every ocean in the world and are found far out to sea. Killer whales may be one of the most fascinating stories in evolution but we have to rely heavily on genetics, photographs, and long field studies of their behavior to put their complicated puzzle together.
In many areas they have developed specialized foraging behaviors, from intentionally beaching themselves to take sea lions in South America to cooperatively hunting schools of salmon returning to spawn in the North Pacific. In the North Pacific, the specialization is documented for the resident and transient groups, the former preferring fish prey and the latter eating marine mammals. In fact, the genetic evidence indicates that the two forms do not interbreed (Hoelzel et al. 1998, Barrett-Lennard 2000) and may be different species (a subject explored in the Cetacean Systematics Workshop. The differentiation is even more extreme in killer whales in the Antarctic. Here, there are three different forms with distinct differences in body size, color patterns and probably food habits (Pitman and Ensor in press). Our preliminary genetic analyses indicate that they also do not interbreed. If this finding is supported by additional data, the recognition of multiple species of killer whales will result. The big challenge, then, will be to determine how the specialized forms from different parts of the globe relate to each other.
The question of how many species and sub-species of killer whales exist is not only a very interesting academic question but has consequences for killer whale conservation. Killer whales that live near Seattle and Vancouver (called Southern Residents) have been declining and were recently listed as endangered under the Endangered Species Act. The decision to list Southern Residents hinged on whether these animals fit the definition of a 'Distinct Population Segment' (DPS) under the Endangered Species Act. The debate over whether or not to list Southern Residents as endangered highlighted the urgent need to better resolve of killer whale systematics. Consequently, our laboratory has undertaken an examination of killer whale teeth from museums to help address questions of historical range of Southern Residents.
Barrett-Lennard, L. G. 2000. Population structure and mating patterns of killer whales (Orcinus orca) as revealed by DNA analysis. PhD thesis, University of British Columbia, 97 pp.
Hoelzel, A. R., Dahlheim, M. and Stern, S. J. 1998. Low genetic variation among killer whales (Orcinus orca) in the eastern North Pacific, and genetic differentiation between foraging specialists. Journal of Heredity 89:121-128.
Pitman, R. L. and Ensor, P. in press. Three different forms of killer whales in Antarctic waters. Journal of Cetacean Research and Management