Changes in biological characteristics of walleye pollock associated with biomass fluctuation in the East Sea during the late 20th century

Abstract

Walleye pollock (Gadus chalcogrammus, hereafter pollock) is one of the popular fishery species in Korea, and Korea is one of the major producer and consumer of pollock. Pollock used to be one of the most dominant fishery species in South Korean waters until the 1980s. However, its catch had rapidly decreased through the 1990s, and eventually, Korean pollock stock was completely collapsed after 2008. Although it was expected that the biological characteristics of pollock would be adjusted in accordance with the biomass fluctuation, the systematic investigation on pollock resources in South Korean waters was not possible because the major spawning ground located in North Korean waters. The National Institute of Fisheries Science (NIFS) has collected information of pollock in the East Sea since the mid-1960s. Using these data, we tried to investigate biological characteristics of pollock during high (1976-1985) and low (1991-2000) biomass periods. Biological characteristics showed density-dependent growth: Dominance of larger size pollock, higher condition factor, and larger length at maturity in the low biomass period. Concurrently, monthly examination of gonado-somatic index (GSI) revealed that there was a density-dependent process in reproductive property of pollock stock in Korean waters.rean waters until the 1980s. However, its catch had rapidly decreased through the 1990s, and eventually, Korean pollock stock was completely collapsed after 2008. Although it was expected that the biological characteristics of pollock would be adjusted in accordance with the biomass fluctuation, the systematic investigation on pollock resources in South Korean waters was not possible because the major spawning ground located in North Korean waters. The National Institute of Fisheries Science (NIFS) has collected information of pollock in the East Sea since the mid-1960s. Using these data, we tried to investigate biological characteristics of pollock during high (1976-1985) and low (1991-2000) biomass periods. Biological characteristics showed density-dependent growth: Dominance of larger size pollock, higher condition factor, and larger length at maturity in the low biomass period. Concurrently, monthly examination of gonado-somatic index (GSI) revealed that there was a density-dependent process in reproductive property of pollock stock in Korean waters.