Recent changes in reproduction are considered for two populations of walleye pollock which spawn in the Japan Sea at the coasts of Primorye and Hokkaido. Interannual dynamics of reproduction for both populations corresponds to the stock-recruitment dependence described by Ricker curve that determines the maximum recruitment with an optimal value of stock equal to the carrying capacity of the biotope for the species and the lower recruitment if the stock is either lower or higher than this optimal value. However, instability of the Ricker curve parameters is noted, and their recent changes were unfavorable for reproduction of both populations and caused decreasing of their stocks, with sharp decline in the early 1990s. Basing on authors results and cited data, climate change in the Japan Sea region is determined as the reason of this decreasing, in particular weakening of winter monsoon. In spite of a common nature, mechanisms of the climate change influence on two studied populations are completely different: reproduction of the Hokkaido population worsened because of increasing transfer of its eggs and larvae out of the Japan Sea in conditions of the strengthening Tsushima Current, that was explained in the terms of Ricker curve as decreasing of population fecundity, but reproduction of the Primorye population worsened because of unfavorable for pollock reconstructions in the local ecosystem located in the south periphery of the Subarctic zone in conditions of increasing water temperature that was explained in the terms of Ricker curve as shrinkage of carrying capacity for pollock (from approximately 150 .103 t to almost zero level). Note that the carrying capacity did not shrink but slightly extended (to 500 .103 t) for the Hokkaido population located in the north periphery of the Subtropic zone. Features of climate warming influence onto subarctic and subtropic ecosystems are discussed.
Distribution and Maturation of Adult Walleye Pollock in Autumn in the Japan Sea off Southwest Hokkaido.