Spatial Distribution and Population Structure of the Pike Esox lucius L. in the Rybinsk Reservoir during the Climate Warming Period

Abstract

Data on the distribution, size and age structure, and growth of the pike Esox lucius collected in the Rybinsk Reservoir in 1953–2015 were analyzed. The main factors that determine the population size of the pike and dynamics of its structural indices are the intensity of the fishery and changes in the temperature regime of the reservoir. Since the mid-1990s, under the influence of high harvesting load, the population of the pike decreased and its age structure changed toward the predominance of individuals of younger age groups. As a result of climate warming, the water column warming of the Rybinsk Reservoir in the 2000s affected the growth character of large individuals. The ratio of phenotypes with small and high number of vertebrae in the first year depends on the water temperature during embryonic development. Among the large individuals preferring deep-water areas with a lower temperature, approximately 50% have 61–62 vertebrae in the axial skeleton. It is suggested that, with climate warming and the development of pike spawn at a higher temperature, the portion of individuals with a high number of vertebrae may decrease, which will lead to a decrease in the number of recruits of the deep-water part of the population.