동해 명태의 자원량 변동에 따른 생태학적 특징 변화

Abstract

Walleye pollock (pollock hereafter) used to be the most dominant species in Korean waters, but catches decreased rapidly since the late 1980s, and the stock was collapsed completely in the early 21st century. To investigate environmental effects on the pollock stock we compared differences in biological and ecological parameters during high (1970s-1980s) and low (1990s-2000s) biomass periods. Water temperatures showed an alternating pattern of warm and cool phases off the coastal areas where the walleye pollock fishery operated. For example, at 200 m, warmphases appeared in the mid 1970s, and early 1990s with cool phases in the early to mid 1980s and since the mid 1990s. Trends in surface water temperature were similar until 1990, but thereafter surface temperature remained warm. Pollock length frequencies showed that a larger size class was dominant in the low biomass period when their condition factor was larger, as well. This indicates that growth was relatively better during the low biomass period. The gonad-somatic index also revealed that the peak spawning season was in February during the high biomass period but changed to December during the low biomass period. Population Stock Density (PSD), which is index of size structure based on length frequency, was higher during the low biomass period than during the high biomass period, indicating recruitment intensity of pollock became weaker in 1990s.fects on the pollock stock we compared differences in biological and ecological parameters during high (1970s-1980s) and low (1990s-2000s) biomass periods. Water temperatures showed an alternating pattern of warm and cool phases off the coastal areas where the walleye pollock fishery operated. For example, at 200 m, warmphases appeared in the mid 1970s, and early 1990s with cool phases in the early to mid 1980s and since the mid 1990s. Trends in surface water temperature were similar until 1990, but thereafter surface temperature remained warm. Pollock length frequencies showed that a larger size class was dominant in the low biomass period when their condition factor was larger, as well. This indicates that growth was relatively better during the low biomass period. The gonad-somatic index also revealed that the peak spawning season was in February during the high biomass period but changed to December during the low biomass period. Population Stock Density (PSD), which is index of size structure based on length frequency, was higher during the low biomass period than during the high biomass period, indicating recruitment intensity of pollock became weaker in 1990s.