Changes in the biological characteristics of walleye pollock related to demographic changes in the East Sea during the late 20th century

Abstract

Walleye pollock was one of the most dominant fish species in Korean waters during the 1970s-1980s, but its catch rapidly decreased from the late 1980s and collapsed in the 2000s. The biological characteristics of fish species tend to depend on their biomass and the environmental conditions. To investigate the changes in the biological characteristics of pollock such as size frequency, condition factor, and maturation associated with biomass levels, as well as the possible causes of the stock collapse in terms of environmental change, we used data collected by the National Institute of Fisheries Science (NIFS) during high (1976-1985) and low (1991-2000) periods of pollock biomass. Density-dependent effects on the pollock population were evident in Korean waters: The pollock were becoming larger and heavier at length during the low biomass period. The gonado-somatic index (GSI) also indicated that the peak spawning season was broad (October to February) during the high biomass period and narrower (December to January) during the low biomass period. The population abundance and recruitment success of Korean pollock appear to have been affectedby the warming of theocean surface from the early 1990s. Thus, we suggest that the biomass fluctuations associated with environmental changes during their early life stages were thought to be responsible for the observed changes in the biological properties of pollock. on their biomass and the environmental conditions. To investigate the changes in the biological characteristics of pollock such as size frequency, condition factor, and maturation associated with biomass levels, as well as the possible causes of the stock collapse in terms of environmental change, we used data collected by the National Institute of Fisheries Science (NIFS) during high (1976-1985) and low (1991-2000) periods of pollock biomass. Density-dependent effects on the pollock population were evident in Korean waters: The pollock were becoming larger and heavier at length during the low biomass period. The gonado-somatic index (GSI) also indicated that the peak spawning season was broad (October to February) during the high biomass period and narrower (December to January) during the low biomass period. The population abundance and recruitment success of Korean pollock appear to have been affectedby the warming of theocean surface from the early 1990s. Thus, we suggest that the biomass fluctuations associated with environmental changes during their early life stages were thought to be responsible for the observed changes in the biological properties of pollock.