Marine mammals in the Sea of Okhotsk: abundance, consumption of resources, and outlook for future studies.

All-Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), V.Krasnosel'skaya 17a, Moscow, 107140 Russia, 

Abstract

Marine mammals play an important role in the Okhotsk Sea ecosystem. They are very abundant in the region, and being high-level predators, consume significant amount of living marine resources. 7 pinniped and about 20 cetacean species inhabit Sea of Okhotsk. Total population of pinnipeds is estimated about 1,5 millions, while abundance of cetaceans is unknown but considered to be over 100,000 individuals. Each marine mammal species has its own ecological preferences, so the range of their diets is very wide and include fish, cephalopods and crustaceans. Annual consumption of prey only by pinnipeds is estimated by different authors from 1,5 to 1,8 million tons, cetaceans also consume up to 2,4 million tons, including over 1 million tons of fish. Therefore, total amount of living resources, used each year by marine mammals in the Sea of Okhotsk appears to be close to 5 million tons (about three times more than fishery catch). There is no whaling in Okhotsk Sea now; commercial sealing is also very insignificant comparing with period of 1960-1990. Harvest operations gave opportunities to collect vast data on age-sex structure, reproduction and other population parameters, so there is a lack of information at present time. Therefore, assessments of marine mammal abundance in the Sea of Okhotsk and monitoring of their populations still remain an urgent task, but nowadays, complex ecosystem approach becomes more and more important. That is why climate changes, prey distribution and abundance, pollution and other environmental parameters should be taken into account in marine mammal studies. Another item is protection of endangered species such as western gray whales. Satellite tracking and tagging is especially crucial to study their migrations. In this case international cooperation is necessary to ensure effectiveness of the studies.

Keywords: pinnipeds, cetaceans, abundance, prey consumption,