Consequences of a sockeye salmon shortage for the brown bear in the basin of Lake Kurilskoe, Southern Kamchatka

We studied the behavioural ecology of Ursus arctos (hereinafter -brown bear or bear) in the basin of Lake Kurilskoe (Kamchatka Peninsula) in the summer and autumn of 2017-2018. The aim of this study was a comparative assessment of the behaviour of brown bears with respect to the heterogeneity of trophic conditions. In 2018, considering an extremely high commercial catch of Oncorhynchus nerka (hereinafter -sockeye salmon or salmon) and high flood in the first half of the summer, the decline in the abundance and availability of salmon led to significant changes in the behaviour and distribution of bears. The success of fishing behaviour of bears in 2018 was found to be lower than in 2017. During the periods of salmon abundance in 2017, solitary bears formed temporary friendly associations that we did not observe in 2018. Due to the increased incidence of intraspecific predation in 2018, bears began to show aggression towards humans. Deterioration of the physical condition of some females and behavioural changes in food-procuring strategies were accompanied by the appearance of abandoned cubs. The peak of negative changes in the bear populations was noted in the first half of September when the energy requirements of bears increased. A modern approach to the development of the resources of sockeye salmon in the Basin of Lake Kurilskoe and River Ozernaya requires a serious revision of the fishing load in accordance with the characteristics of the population structure of sockeye salmon and its exclusive role in the local ecosystem. It is necessary to reconsider the optimal number of sockeye salmon allowed into the Lake Kurilskoe and its tributaries. The current practice of cancelling the passing days during which salmon can migrate unobstructed into and up the River Ozernaya towards Lake Kurilskoe is unacceptable.