Fluctuations in abundance of common squid, Todarodes pacificus in the Far East.

Long term fluctuations in the abundance of common squid, Todarodes pacificus are taken in the waters around Korea and Japan from 1952 to 2003. The year-to-year fluctuations in the abundance in the Tsushima Warm current (TWC) region (Yellow sea- east China sea-east/Japan sea) revealed the same pattern with that in the Kuroshio-Oyashio Current (KOC) region (Northern Pacific) except for the period of fishing shifts from the KOC to TWC region in the late 1960s and 1970s. Two period of high abundance in the entire fishing regions emerged in the 1950s-1960s and 1990s, in-between there has been a low level in the KOC region for 20-years (1970s-1980s) and in the TWC region for 10-years (1980s). The squid fishery in the marginal zone of the distribution range (KOC region) was mainly based on winter-breed microcohort that collapsed earlier (from the early 1970s) than that of the fishery in the central zone (TWC region), based on autumn and winter-breed microcohorts from the mid 1970s. During the low abundance period (1980s) the catch rates of the autumn microcohort were higher than those of the winter microcohort, while the abundance of the two increased schynchronously from the early 1990, suggesting the possible homogeneity of the population structure during the high abundance period.

Ecosystem structure and trophic level to the oceanographic conditions around the waters of Jeju Island.

The water around Jeju Island was characterized by the Tsushima warm current (TWC) being high temperature and salinity and the Yellow sea cold bottom water (YSCBW) being low temperature and salinity We investigated the diversity indices, community structures and trophic level of fish species collected by trawl net in the waters around Jeju Island during April 2004-August 2005. We also presented ecosystem structure estimated by combination of trophic level and the oceanographic condition. There were totally distributed 301 species in the survey area during April 2004-August 2005, regionally 151-229 species in TWC and 75-154 in YSCBW. Shannon's diversity indices (H') of TWC were 2.95-3.39, being higher than those of YSCBW (2.11-2.40), and species richness (R) of TWC were 10.93-18.33, being also higher than those of YSCBW (6.96-12.48), except the values of October 2004. A total of 7429 individuals of 98 species was seasonally examined for their dietary composition in the survey area during 2004-2005. Of which, 3,682 individuals were observed with prey organisms. Standardized diet composition and trophic level estimates were calculated for predators in the survey area being influenced by TWC and YSCBW Trophic level values were diverged with range from 3.23 of the small pelagic to 4.39 of the goose fish, depending on the taxonomic group. The analysis of trophic level values showed that ecosystem structure was different between TWC and YSCBW during April 2004-August 2005.