Impacts of environment changes on walleye pollock in the East Sea

Abstract

In Korea, walleye pollock (Gadus chalcogrammus, hereafter pollock) was one of the popular fisheries species until the 1980s, which afterward the stock biomass has considerably decreased, resulting in the pollock stock collapse after 2008. For the possible causes of the collapse, three hypotheses have been suggested: overfishing, warming of seawater, and changes in ecosystem structure/function. In this study, we tried to examine how the collapse of pollock was related to environmental changes in Korean water using atmospheric data (air temperature and wind speed) from Korea Meteorological Administration and oceanographic data (sea surface temperature and zooplankton abundance) from Korea Oceanographic Data Center. A cumulative sum analysis of the air temperature, wind speed, and sea surface temperature indicates that there is a regime shift in the late 1980s when phytoplankton and zooplankton population also substantially increased. In addition, we found that days for warm water higher than 12˚C in April, which is probably associated with low survival of pollock in early life stage, more frequently occurred after the late 1980s. These changes seem to be related to Arctic Oscillation (AO). Our findings suggest that the environment changes in the late 1980s contribute to the stock collapse of Korean pollock.or the possible causes of the collapse, three hypotheses have been suggested: overfishing, warming of seawater, and changes in ecosystem structure/function. In this study, we tried to examine how the collapse of pollock was related to environmental changes in Korean water using atmospheric data (air temperature and wind speed) from Korea Meteorological Administration and oceanographic data (sea surface temperature and zooplankton abundance) from Korea Oceanographic Data Center. A cumulative sum analysis of the air temperature, wind speed, and sea surface temperature indicates that there is a regime shift in the late 1980s when phytoplankton and zooplankton population also substantially increased. In addition, we found that days for warm water higher than 12˚C in April, which is probably associated with low survival of pollock in early life stage, more frequently occurred after the late 1980s. These changes seem to be related to Arctic Oscillation (AO). Our findings suggest that the environment changes in the late 1980s contribute to the stock collapse of Korean pollock.