Fish and Fisheries

Abstract

The East Sea (Japan Sea) is a physically dynamic regional sea, and fish communities have adapted to the variety of habitats that characterize the Sea. There are various opinions about the number of fish species in the East Sea. Although the recent tendency for increasing occurrence of subtropical species is likely due to ocean warming, it has been generally understood that about 400–500 fish species, including some brackish water or anadromous species, reside in the East Sea. Warm water pelagic species such as anchovy and chub mackerel occupy the surface layer in the south, while coldwater species such as chum salmon reside in the surface layer of the northern East Sea and subsurface water column in the whole East Sea. The annual fish catch statistics from the entire East Sea have not been available because of the political obstacles currently existing among neighboring nations. However, historic catch records indicated that pollock was a dominant species exceeding about 3 million metric tons (MT) from the whole East Sea during the 1980s. Pollock biomass seems to be much reduced since the 1990s. The Japanese fish catch in the East Sea indicated that fish production increased greatly after 1970, and reached a peak of 1.76 million MT in 1989. Then, it decreased abruptly with the sardine collapse, and remained at about 500,000 MT in the 2000s. In Japanese waters, the fish community structure changed evidently around the late 1980s with warm-water species increasing and cold-water species decreasing. The annual catches of Korean East Sea fisheries showed a peak of 275,000 MT in 1982 and then gradually declined until the early 1990s due to the decline of pollock stock. After that, the annual catches started increasing with the increase in common squid, which comprised 45 and 55 % of the Korean East Sea fisheries in the 1990s and 2000s, respectively. This shift of dominant species caused a continuous decreasing trend in trophic level. Recently, Korean catches fluctuated around 200,000 MT annually. The climatic regime shifts (CRS), which occurred in the mid 1970s and the late 1980s, caused changes in the structure of the East Sea ecosystem. In Korean waters, the 1976 CRS was manifested by a decrease of saury population, but an increased biomass and catch production of sardine and filefish. Correlation studies have found that high saury and sandfish catches occurred during periods when the Southern Oscillation Index was generally positive (i.e. La Nina conditions), when the mixed layer depth was shallower, and when the catches of sardine and pollock were low. Results from a mass-balance model (ECOPATH) indicated that the mean trophic level increased from 3.09 in the pre-1976 CRS period (1970–1975) to 3.28 in the post-1976 CRS period (1978–1984) due to the increase of high trophic level species such as pollock. Also, the biomass and production of fisheries resources in the southwestern East Sea changed before and after the 1988 CRS. Due to overfishing or seawater warming in the East Sea, the fish biomass in the East Sea seems to be reduced in recent years. Implementation of a proper management scheme using ecosystem-based fisheries assessment and international cooperation in data exchange and scientific surveys would increase the likelihood of sustainable utilization of fish resources in the East Sea.