Climate change and fluctuations of pelagic fish populations in the Far East region

Time series of ocean climate indices and catch records were used to identify the alternation patterns of pelagic fish populationsin relation to climate regime shifts. During 1910-2008, an orderly alternation of dominant pelagic fish groups wasobserved in the Tsushima Warm Current (TWC; Yellow Sea-East China Sea-East Sea/Japan Sea) and Kuroshio-OyashioCurrent (KOC; Northwestern Pacific) regions. After the collapse of herring fishery in the late 1920s, the sardine (A group)dominated in the 1930s, 3 other species (C group; Pacific saury, jack mackerel, and anchovy) dominated in the 1950s-1960s, chub mackerel (B group) dominated in the 1970s, and then sardine (A group) dominated again during cool regimein the 1980s. As sardine biomass decreased in association with the climate regime shift that occurred in the late 1980s,catches of C group immediately increased after the regime shift and remained at high levels during warm regime in the1990s. Alternations of dominant fish groups occurred 6 times between 1910 and 2008. The dominant period of the 7 specieslasted for 10-20 years. The catch of Pacific sardine in the TWC and KOC regions showed a negative correlation withthe catch of the other 5 species (Pacific herring, anchovy, jack mackerel, Pacific saury, and common squid), suggestingthat the abundance of the 5 species is strongly affected by the abundance of Pacific sardine in relation to the climateregime shifts. The total catch level of the 7 species in the KOC region was generally higher than that in the TWC regionbefore 1991 but was lower after 1992, suggesting that the fish populations in the Pacific side are shifted to the TWC regionby zonal oscillation of the oceanic conditions in relation to the climate regime shift in the late 1980s.