Cannibal killer whales: scientists have discovered a previously unknown behavior pattern of whales on Commodores
The World Day for the Protection of Marine Mammals is celebrated on February 19. On this day, we tell about another unusual find in the field of studying marine mammals on the Commander Islands.
There are two ecotypes of killer whales in the Russian waters of the Northern Pacific – fish-eating and carnivorous. Ecotypes differ in appearance, genetics, acoustics, social structure, and food specialization. The diet of the carnivorous killer whale includes representatives of various species of marine mammals: long-eared and real seals, cetaceans, walrus, sea otter. Carnivorous killer whales of different populations have diverse feeding strategies determined by specific conditions, species, and prey availability. Killer whale hunting for the northern fur seal was regularly observed in the waters of the Commander Islands, cases of attacks on white-winged porpoises and antlers were recorded, and a dead killer whale was found with several sea otters in its stomach. There was no hunting of killer whales on their own kind in the local water area.
In general, the world’s first and currently the only direct record of killer whale killing of a representative of its species was made in the waters of British Columbia. From aboard the motorboat, scientists conducted lengthy and detailed documented observations of the interaction of two families of carnivorous killer whales. During this, a male from one family group killed and abducted a newborn cub from another group. But there were no signs of killer whales eating the dead cub.
The finds on Bering Island turned out to be all the more intriguing. In addition to visual observations of killer whale hunting, indirect evidence of predation is the discovery of fragments of marine mammal bodies. Biologist Sergey Fomin, as part of his work on monitoring the coastal mortality of marine mammals, which he has been conducting on the Commanders for more than 20 years, has recorded five cases of cetaceans with signs of being eaten by killer whales. Among the discovered remains are body parts of northern finfish, unidentified cetaceans and, twice, the remains of an orca, which brings us back to the question of cannibalism within this species.
The first find on Bering Island was the dorsal fin of a killer whale with a piece of skin and a subcutaneous fat layer, according to external signs, the remains belonged to an individual of a fish-eating ecotype. The freshness of the remains allowed us to assert that the killer whale was eaten very recently, directly in the waters of the Commander Islands. The teeth marks were also carefully studied by scientists, as a result of which they came to the conclusion that the marks were left by killer whales – they did not fit the description of any possible predator of this size.
It is difficult to say for sure whether this was the result of carnivorous killer whales hunting a representative of their own species, albeit of a different ecotype, or whether they decided to eat a killer whale that died for a different reason. Some time later, another dorsal fin of a male juvenile killer whale was discovered, which was significantly larger than the first one, but also had characteristic markings from killer whale teeth.
In total, in the world history of marine mammal research, there have been only three cases confirming the cannibalism of killer whales, and all of them belong to Russian scientists. The first such mention (which remained the only one for many years) – the eating of killer whale cubs by males – was described by the Soviet scientist V.I. Shevchenko: “The material was collected on the Antarctic whaling flotillas Slava and Sovetskaya Ukraina from 1962 to 1974. <…> Research was conducted in three directions: a) analysis of the stomach contents of killer whales; b) visual observations of the behavior of whales at sea; c) inspection of whale carcasses in order to identify wounds and scars from killer whale bites. <…> In the moderately warm zone (30-50 gr. South) in March-April, 30 stomachs were examined. <…> It is possible that due to the poor food supply in the warm zone, cases of cannibalism have also been reported here: two males taken from the same group have the remains of a killer whale with a length of about 320 cm.”
Since the case of killer whales eating representatives of their own species is no longer an isolated one, it characterizes the complex intraspecific relationships of killer whales in the waters of the Commander Islands, and possibly in general. These findings are likely to shed light on the behavior of different killer whale ecotypes in relation to each other. Previously, scientists have repeatedly observed that carnivorous and fish–eating killer whales try to keep apart, not contacting each other – apparently, there are very good reasons for this. But we still have to reveal all the secrets of their behavior.
Galina Zhikhoreva, newspaper “Aleutian Star”, for Kamchatka.Today