One of the best places of the world to see orcas in the wild is British Columbia. These orcas have been studied for 38 years and although many aspects about their lives remain unclear, some of them are well known. Thanks to Dr. Michael Bigg who first used the photo-ID technique to identify whales individually by their dorsal fin shapes and back patches, scientist have been able to distinguish different populations, lifestyles and social structures. Also, we can distinguish different killer whale populations by their vocalisations. These vocal variations are known as dialects and are used by the whales for communication and as acoustic indicators of group identity and membership. This last function could serve to preserve the integrity of the social unit and also to prevent consanguinity.
In BC waters we can find three distinct populations of orcas: Residents, Transients and Offshores. Resident orcas feed predominantly on fish with a clear preference for salmon (mainly chinook) during spring through fall. Their primary range is the coastal region of Washington, British Columbia and southeastern Alaska distinguishing between the Northern and the Southern Resident Community. While the Southern residents are mainly found off the southern half of the Vancouver Island and Puget Sound, the Northern residents are primarily found from the northern half of Vancouver Island to 
Frederich Sound in Alaska. These orcas live in groups that are organized along lines of maternal relatedness. Taking this into account, we can organize their societies into a series of social units, from small to large, on the basis of these genealogical relationships. The matriline is the smallest unit formed by closely related whales linked by maternal descent. The next unit is the pod which is a group of related matrilines that possibly have a common maternal ancestor in a recent past. Then comes the clan formed by pods with similar vocal dialects and finally the top social level, the community consisting of pods that normally associate with one another. Though, this social structure is not static, it can change slowly but constantly.
Transient orcas feed on marine mammals and sometimes seabirds. Their known distribution goes from coastal areas from Southern California to the Auletian Islands in Alaska. Compared with residents, transients have a very fluid social order, and they mix with each others within the community. A whale that is born in a group does not necessarily stay with that group for life and they tend to travel in small groups of two to six or occasionally alone. They also hunt in small groups so they keep in touch in silence to avoid detection by their preys. So, transients are very quiet compared to residents but they do vocalize in certain situations. This vocalisations are very similar in structure and function to those used by resident orcas.
This is a video I recorded of a group of transient orcas near Alert Bay.
Offshore orcas are normally found in large groups of 30 to 60 whales and rarely seen in protected coastal waters. As for their diet, it is not clear if they feed on fish or either marine mammals. They prey on salmon for at least a part of the year and vocalize quiet frequently so we could think they are fish eaters.
Although the ranges of the three populations overlap, DNA studies indicate these populations are distinct. Transients are very distant from residents and offshores, likely representing thousands of years of reproductive isolation. Offshores are closer to residents but are anyway distinct.
If you’d like more information about BC killer whales I would recommend two books which apart from general information include catalogues for individual whale identification (Available in Amazon):
- Ford, J.K.B., G.M. Ellis, and K.C. Balcomb. 2000. Killer Whales. Second Edition. UBC Press.
- Ford, J.K.B., and G.M. Ellis. 1999. Transients: Mammal-Hunting Killer Whales. Second Edition. UBC Press.
Also, you can download updated catalogues and information from this website: http://www-sci.pac.dfo-mpo.gc.ca/sa/cetacean/default_e.htm.
