Two Orca Populations In North Pacific Ocean Are Two Distinct Species, Study Finds

Experts said that two distinct populations of orcas in the North Pacific Ocean are two distinct species.

Killer whales (Orcinus orca) are currently recognized as a single ecologically and morphologically diverse, globally distributed species.

Morphological Data

Previous studies have shown that multiple morphotypes or ecotypes have been described, often associated with feeding specialization, and several studies have suggested taxonomic revision to include multiple subspecies or species in the genus.

Experts reviewed the ecological, morphological and genetic data for the well-studied 'resident' and Bigg's (aka 'transient') ecotypes in the eastern North Pacific and used quantitative taxonomic guidelines and standards to determine whether the taxonomic status of these killer whale ecotypes should be revised.

''Our review and new analyses indicate that species-level status is justified in both cases, and we conclude that eastern North Pacific Bigg's killer whales should be recognized as Orcinus rectipinnus (Cope in Scammon, 1869) and resident killer whales should be recognized as Orcinus ater (Cope in Scammon, 1869),'' the study indicated.

Based on the combined lines of evidence presented above, scientists recommended that resident and Bigg's killer whales be recognized as species distinct from the globally distributed O. orca and from each other.

They pointed out that prior species designations, typically based on a single skull, have all been synonymized under O. orca, and there are no prior subspecies designations or holotypes within killer whales of the North Pacific.

Three types have been attributed to the North Pacific though some experts indicated that they doubted the origin of the specimen for O. pacifica, and the mitogenome haplotype of this specimen is most similar to Antarctic type B haplotypes.

Meanwhile, the other two binomials from the Pacific (Orca ater, Orca rectipinna) are essentially based on visual observation and are not associated with available type specimens.

As the two binomials are described in the same publication with no prior names from the North Pacific, they proposed Orcinus ater and Orcinus rectipinnus, for the resident and Bigg's species, respectively. They also discussed the history and use of these binomials.

Most Efficient Predators

While killer whales represent some of the most efficient predators the world has ever seen, experts have said science is still unraveling the diversity among them.

The identification of additional killer whale species is likely to follow. One leading candidate may be "Type D" killer whales identified in the Southern Ocean around Antarctica, studies have shown.

Other killer whales in Antarctic waters also look very different from the best-known black and white killer whales. This reflects a wider diversity within the species, which has used drones to study killer whales around the world.

The different prey of the two species may also help explain their different trajectories, according to the study.

Southern Residents are listed as endangered in part because of the scarcity of their salmon prey. Bigg's killer whales, by contrast, have multiplied while feeding on plentiful marine mammals, including California sea lions.