동해 명태(Gadus chalcogrammus)의 자원량 변동에 따른 생물학적 특성 변화

Abstract

Walleye pollock (Gadus chalcogrammus, pollock hereafter) used to be the most dominant species in Korean waters, but its catch decreased rapidly from the late 1980s, and the stock was collapsed completely in the early 21stcentury. To investigate the environmental effects on pollock stock we compare the differences in biological and ecological parameters during high (1970s-1980s) and low (1990s-2000s) biomass periods. Water temperature showed an alternating pattern of warm and cool phases off the coastal areas where the walleye pollock fishery operated. For example, at 200 m, warm phases appeared in mid 1970s, and early 1990s while cool ones in early-mid 1980s and after mid 1990s. There are similar trends in surface layer until 1990, but water temperature maintained warm regime after 1990s. Observation on length frequency of pollock showed that the larger size class was dominant in low biomass period, and the condition factor was larger at the same period. This indicates that growth was relatively better in the low biomass period. Gonad-somatic index also revealed that peak spawning season was February in high biomass period but it seemed to be changed to December in low biomass period. Population Stock Density (PSD), which is index of size structure based on length frequency, was higher in low biomass period than high biomass period, indicating recruitment intensity of pollock became weaker in 1990s.