Since 1970 scientists have believed that there are three separate races of orca. A race, or subspecies, is described as a geographically isolated sub-population of a species consisting of animals that interbreed with one another. Yet the three races of Orcinus orca appear to have radically different behavior, distribution, social organization and acoustic signals. In fact, rather than interbreeding, they have been observed actively avoiding each other and even swimming in opposite directions when encounters take place. This behavior, which is extremely unusual for any mammal, has given rise to questions about their evolution. Some experts believe that the races are on different evolutionary paths and may already be separate species. Continuing studies, based on genetic testing, will soon resolve the debate.
Most of our information about orcas has been gathered from studies of 'resident' orcas in Southern Washington and Southeastern Alaska. Residents are defined as groups of orcas that live in extremely stable groups, or pods, of between 10 and 50 animals, and remain together for their entire lives. Resident pods remain within clearly defined areas and have a range of about 300 miles for specific periods during the year. They are extremely vocal, exhibiting different dialects according to pod. They rarely dive for longer than 3 to 4 minutes and feed exclusively on fish. Their dorsal patches are mottled and contain various amounts of black ['open'] patches, and their dorsal fins are curved backwards. Residents may have evolved in areas where food supplies are abundant and there is an advantage to remaining with a large group. Pod membership facilitates the location of fish and also allows orcas to pass down specific hunting knowledge from generation to generation.
In contrast, 'transient' orcas travel alone or in much smaller groups of between 2 and 5 whales, and exhibit a much looser social organization. Although their range is less certain, transients are known to travel more widely than residents and make much less predictable appearances. The transients of the Pacific Northwest are thought to travel in a range of 900 miles. Transients primarily hunt large marine mammals, including the largest baleen whales, and appear to avoid fish as a food source. These whales spend less time at the surface and dive on average for 5 to 7 minutes, with some dives lasting as long as 15 minutes. Transients are markedly less vocal than residents, probably due to their choice of prey, and all share a common dialect. Their dorsal fins are triangular and generally more pointed than residents with larger, solidly gray saddle patches.
The third, more recently discovered, race of orca is the 'offshores', which live in much larger groups of 30 to 60 whales and prefer open waters to the protected coastal waters where residents are seen. Offshores are presumed to feed predominantly on fish because of their location, although marine mammals may be an additional food source. They bear more physical resemblance to residents than transients, but may be somewhat smaller and may have dorsal patches that are either uniformly gray or 'open'. Their dorsal fins are also continuously rounded over the tip and lack an acute angle at the rear corner.
