Killer whale

Killer whale (Orcinus orca) is a largest species from family Delphinidae. Killer whales are found in all oceans from Arctic and Antarctic regions to tropical seas, but most common in high-productive temperate and subpolar waters. Killer whales as a species have a diverse diet, although individual populations often specialize in particular types of prey. Some feed exclusively on fish, while others hunt marine mammals such as sea lions, seals, walruses and even large whales. In our area two ecotypes of killer whale occur - fish-eating (R-type) and mammal-eating (T-type ), which were recently proposed to be a separate species.

R-type killer whales feed primarily of fish. In Kamchatka waters feeding on Atka mackerel and Chum salmon was documented. R-type orcas have very close, long-term family associations. Males and females both swim with their mothers their entire lives, so mating only happens when multiple pods come together for a few hours or days, and those associations are only temporary.

R-type killer whales use vocal dialects to keep their pods together. Some calls are unique to only a small pod of 6 or 7 animals. Others may be used by a whole clan, or extended family group of 30-50 animals.

T-type killer whales feed primarily of marine mammals, including seals, sea lions, porpoises, and other whales. They usually have a larger range than R-types, and in some cases may travel over a thousand miles, but they also have areas where they visit frequently.

T-type killer whales have social structure that is less defined than R-type orcas, and usually swim in smaller groups of 1 to 7 animals. While R-type orcas are often vocal, T-type killer whales travel quietly so that they do not alert their prey. There are far fewer T-type killer whales than R-type orcas. The dorsal fins of T-type often have a more triangular shape, while R-type orcas have dorsal fins that are more curved and have a more rounded tip.

We have analyzed photographs and biopsy samples from R- and T-type killer whales collected over the years 2000-2017. Comparing catalogs from different regions allowed to estimate the level of interchange both for the R-type and T-type killer whales. We have documented the movements of individually identified R-type killer whales between northeastern and southeastern Kamchatka and the Commander Islands, and movements of individually identified T-type killer whales between Kuril Islands and eastern Kamchatka and across the Okhotsk Sea.

Genetic analysis demonstrated clear differentiation between R-type and T-type killer whales, confirming the absence of mating between ecotypes. Haplotype diversity of R-type killer whales was much lower in the Russian Pacific than in the Aleutian Islands and the eastern North Pacific. Haplotype diversity of T-type killer whales was higher, than in R-type killer whales. In general, it appears that R-type killer whales of the Russian Pacific belong to the same population that colonized the area relatively recently (probably after the Last Glacial Maximum).

Our data demonstrate that geographical segregation exists among R-type and T-type killer whales in the Russian Pacific. R-type whales prevailed in the waters of eastern Kamchatka, Commander and Kuril Islands and in the central Okhotsk Sea, while T-type whales dominated the waters of Chukotka and the coastal Okhotsk Sea. The most prominent difference between these areas is depth: the regions dominated by T-type whales are represented by wide shallows covered with ice in winter, while in the regions where R-type whales prevail, deep waters occur close to shore. These differences have not been demonstrated previously for the well-studied killer whale populations in the eastern North Pacific. This is especially important for the management and conservation of the species, because captures of killer whales for dolphinariums take place in the western Okhotsk Sea, where only T-type whales occur. The overall encounter rate for T-type killer whales was much lower than for R-type whales, similarly to the eastern North Pacific. Preliminary estimate of abundance of T-type killer whale stock in the western Okhotsk Sea showed small numbers of about 240-260 animals, suggesting that no further live-capturing should be performed.

Humpback whale

Killer whale

Sperm whale

Baird's beaked whale

Dall's porpoise

Minke whale