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

ABSTRACT

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.