What caused the collapse of walleye pollock population in Korean waters?

Walleye pollock (pollock hereafter) in Korean waters was one of the most important fishery species economically, and the majority of population located in North Korean waters. Catch records have been changed dramatically since commercial fisheries begun in the early 20th century: the highest catch in 1930s, sudden decrease during 1940s~1960s, another boom in 1970s~1980s, and a continuous decrease in 1990s until they collapsed completely in 2000s. Three plausible hypotheses were introduced for such collapse: overfishing on pollock in high biomass period, warming of seawater, and changes in ecosystem structure and function. Those hypotheses reviewed would give us clues how Korean pollock population survive in ecosystem, and such theoretical backgrounds should be the basis for the establishment of conservation measures with precautionary concept when pollock return to Korean waters again. Intensive interdisciplinary collaboration between South and North Korea is recommended for predicting their re-visiting and for better management under changing environment.