Occurrence of killer whales Orcinus orca off the Commander Islands and Avacha Gulf from 2008-2021 and its relation to the sea otter Enhydra lutris population decline

Killer whale is an apex predator which plays an important role in marine ecosystems. In the Russian waters, killer whales are represented by two ecotypes - fish-eaters (R-type) and marine -mammal eaters (T-type). In our study we focused on two study areas: Commander Islands and Avacha Gulf of Kamchatka. The numbers of some species of marine mammals in the North Pacific are declining, and mammal-eating killer whales are often blamed for the decline. For example, the decline in the numbers of sea otters in Alaska is linked by some specialists to the increased predation of mammal-eating killer whales. In the Commander Islands, a decrease in the numbers of sea otters has also been observed in recent years. We analyzed the number of sightings of killer whales in the Commander Islands and Avacha Gulf to find out whether the occurrence of mammal-eating killer whales increased during the study period 2008-2021. We found no definite trend in the occurrence of mammal-eating killer whales over time in both areas. We conclude that our data provide no support to the hypothesis that the decrease of sea otter numbers in the Commander Islands was caused by the increased killer whale predation.