Some Population Dynamics Issues of Pink Salmon Oncorhynchus gorbuscha Temporal Forms on Sakhalin and the Southern Kuril Islands

Abstract

Population dynamics of early and late temporal forms of pink salmon Oncorhynchus gorbuscha on the Iturup and Kunashir islands (southern Kuril Islands) and on the southeastern coast of Sakhalin in 1991–2017 is considered. The periods of the increase and decrease in the abundance of pink salmon in odd and even years occurred simultaneously. However, the duration of periods with high abundance of the early form was shorter. The sharp decrease in the abundance of each of the temporal forms was often due to the effect of extreme environmental factors (flash floods in rivers that wash out the soil on spawning grounds or storms in the coastal zone during the feeding period of juveniles that had recently migrated downstream from the rivers); however, the causes remained unclear in some cases. The abundance of the early form tends to decrease more intensively or one to two generations earlier than the reduction of the more numerous late form; therefore, the emergence of depression signs in the early form may indicate the coming general depression of pink salmon stocks in the area under study.