There appear to be three distinct populations of orcas found in the
waters of the Pacific Northwest. In the early stages of Orca Survey, researchers
encountered killer whales in pods containing 10 to 25 or more whales that
had movement patterns that were fairly predictable during the summer months
and these killer whales were observed feeding on salmon. These were named
the resident killer whales. Occasionally groups of 2 to 5 individuals were
encountered whose patterns of occurrence and movements were erratic. These
killer whales were observed feeding on the seals, sea lions and porpoises
found in the Greater Puget Sound waters. These killer whales were called
transients killer whales. On August 26, 1990 another group of killer whales
were discovered that did not match the ID catalogues of either the residents
or the transients. It is believed that these whales form a distinct race
and they are called the offshore killer whales
The ranges of residents, transients, and offshores overlap, but they
have never been seen to mix. It is now believed that transients and residents
are so different in their behavior, social organization, and ecology that
scientists are speculating that they are separate subspecies on the evolutionary
path towards becoming distinct species. Presently, little is known about
the offshores so it is unknown yet how they fit into the overall picture
although there is speculation that they may be related to the residents.
The preliminary DNA evidence suggests that Northern residents derived
from one matriline of offshores and Southern residents derived from a different
matriline of offshores.
The three populations of orcas can be distinguished physically by close
observation of the dorsal fin and saddle patch. The dorsal fin and saddle
patch of an orca are its fingerprints and individuals within each population
can be distinguished by these two unique features.
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