The species composition and structure of marine mammals within the area of fishing of walleye pollock in the Sea of Okhotsk in 2017 was considered. Eleven species of marine mammals with the total number of 1306 individuals are recorded in the area. Steller sea lion was the most frequent (46.8%) in the records, and following next frequent species are: northern fur seal (13.3%), largha seal (8.9%), minke whale (8.4%) and ribbon seals (7.9%). Effects of specialized trawl fishing on the marine mammals were described, and specifics of interacting with fishing vessels was figured out. Four species among eleven recorded demonstrated various interest or reactions to fishing vessels when approaching the fleet. Steller sea lions and minke whales demonstrated obvious interest to activities of fishing vessels, keeping somewhere near feeding on the fish falling out of trawls or on waste from catch processing, largha seals and lionfishes were indifferent to the fishing fleet, but activities of the fleet near the ice edges made them visibly nervous. No cases of accidental catching marine mammals into the fishing gears recorded.

A review of literature on the diet of Steller sea lion in different seasons of year either on the American continent or in Russia and on the role of walleye pollock in the diet was made. Analysis of the current state of sea lion populations in Russian waters is made, and an expert estimation of sea lionsʼ consumption of walleye pollock in the Sea of Okhotsk is provided; evaluation of the impact on walleye pollock fishery for sea lions is made.

Analysis of published sources and own data on the intensity of fisheries and records of cetaceans in the Western Bering Sea and Eastern Kamchatka from 2003 to 2017 was conducted. Cetaceans were observed throughout the aquatic area mentioned, and the highest number of records were made between the coast of Kamchatka and the Commander Islands and around the islands. The most intensive fisheries operated on the shelf off Cape Navarin. In view of cancellation of the drift nets fishing, overlapping between the areas of intense fishing by all fishing gear and the sites of associated records of cetaceans does not exist for major part of the area considered.

The effects of largha seal in the estuary zone of the Ozernaya River was evaluated. Data on traumatizing of salmon by different predators were analyzed, consumption of salmon by largha seals in the estuary zone was evaluated. A review on the literature data is provided concerning the problem of protecting the catches from marine mammals; it is suggested to work out a method of protecting the catches from largha seal predation, appropriate for conditions in Russian Far Eastern seas.

The article describes results of the long-term regular coastal observations of marine mammals carried out in the entrance part of Kresta Bay from the western point of Meeskyn Spit Island (Cape Meeskyn) and Village Uelkal in summer and fall seasons in 2003, 2005–2009. The mammals recorded in the area of the observations were: gray whale (n = 466), minke whale (n = 48), humpback whale (n = 5), killer whale (n = 173), beluga (n = 11), largha (n = 694), bearded seal (n = 48), ringed seal (n = 43), ribbon seal (n = 1), Steller sea lion (n = 4), northern fur seal (n = 1), polar bear (n = 10). The most regular species observed in the area mentioned during the period from July to September were largha and gray whales. The small-numbered species such as ringed seal, bearded seal, killer whale and minke whale, were seen quite rarely. There were individual cases of coming northern fur seal, Steller sea lion, ribbon seal, beluga and humpback whale. Different use of the water area by marine mammals associated with later and earlier sea ice breakdown in Anadyr Gulf has been found. In 2007 (early ice breakdown), the number of gray whales, minke whales and killer whales was as 2–4 times as higher comparing to the other years. Dead marine mammals (one bowhead whale, one beluga, 9 larghas, 3 bearded seals, 4 ringed seals) and harvested by native people Chukotka in the entrance to Kresta Bay area in period of observation (14 gray whales, 17 bearded seals, one ribbon seal, one northern fur seal) were recorded.

Information about seasonal distribution and migrations of bearded seal in the Pacific sector of Arctics is limited despite an important role of the species as a sourse of nutrition for people of the North. Coastal observations of bearded seals (Erignathus barbatus) took place from different settlements situated on Chukotka Peninsula in 1993–1996, 1998–2000, 2002–2005 and 2010–2011. These observations resulted in collecting data about spatial and temporal distribution, movements and relative number of bearded seals in the coastal zones. In winter, bearded seals have been aggregating on young ice in the northern Gulf of Anadyr. In spring period (April–May) the most dense aggregation of the animals is near Nunligran Settlement (Cape Amchen). In spring and early summer bearded seals migrate toward Bering Strait from the Gulf of Anadyr. The migration toward the strait and northward continues during the period of open water and stops by August. In summer months (August and September) the animals can be seen sporadically. Poorly espressed autumn migration in the coastal zone of Chukotka takes place in October–December. The northern Gulf of Anadyr is one of wintering sites for bearded seals. The research indicates spring migration from the gulf to the Chukchi Sea through the Bering Strait.

The research was based on our observations at the Pacific walrus rookery on Cape Vankarem (the Arctic coast of the Chukchi Sea) from August 6 to October 15, 2018. The number of the animals on the shore and in the water wеre estimated daily from images taken by a DJI Phantom 4 Pro Plus quadrocopter, and with the use of binoculars and panoramic images as well. Coastal mortality of the animals and age and gender composition of the group was also recorded and evaluated. In 2018 the animals had been arriving to the rookery a week later (August 6) than in 2017, but due to warm weather, the rookery functioned approximately 10 days longer (until October 26). The rookery worked during 90 days in 2018. In 2018, same as in 2017, the number of newborn pups in the period of mass migration of females with calves was 7.4%, what is rather high. The maximum number of walruses on the rookery (23 072 individuals, including the animals in the water), was observed on the 9th of October, what is about 10 thousand less than in the same time during the mass migration in 2017. In 2018 the number of dead animals at the rookery was approximately 350. The major part (72.6%) consisted of yearlings, including 64.7% of males and 35.3% of females. The part of adult animals (older than 6 years) was 21.1%, including 64.0% of females and 34.0% of males. The part of calves from 1 to 3 years was 5.7%. In 2018, similar to 2017, there were cases of miscarriage (13) observed on the rookery.