Taking advantage of these differences, biologists studying killer whales off British Columbia in the early 1970s began to identify individuals based on the size and shape of the dorsal fin, the saddle patch pattern, and any nicks and scars. By taking photographs of the killer whales encountered during their summer observations, biologists have built up catalogs of known individuals. Today the total known killer whale population in the Pacific Northwest including Alaska is about 1,000. The ability to track the behavior of individual killer whales has led to several surprising discoveries. By the early 1980s it was clear that the coasts of British Columbia and Washington state is home to two populations that share the same waters but lead completely separate lives.
Transients eat primarily marine mammals while residents prefer salmon.
Hunting these types of prey requires vastly different techniques, which in turn has led to widely divergent social structures. The 170 known transient killer whales in the Pacific Northwest have a fluid social structure and their whereabouts are unpredictable. Pods typically have fewer than 10 individuals and may contain varying combinations of adults and young. Adolescents often leave after the birth of a younger sibling, and adult males often travel alone. Seen from the coastal waters of Mexico to the Bering Sea, transients roam bays, small coves, and channels in search of harbor seals, sea lions, and porpoises.