GROWTH STRATEGIES OF THE SWORDTIP SQUID, UROTEUTHIS EDULIS, IN RESPONSE TO ENVIRONMENTAL CHANGES IN THE SOUTHERN EAST CHINA SEA-A COHORT ANALYSIS

Studies of the biology and population structure of the swordtip squid, Uroteuthis edulis (Hoyle, 1885), have been performed along the southwestern edge of the Sea of Japan to the South China Sea, but limited information is available on how environmental variation affects the seasonal cohorts. The size and growth rates of seasonal cohorts of the swordtip squid in the southern East China Sea were investigated using samples obtained from commercial catches and research fishing vessels during the period from February 2006 to November 2010. Cohorts that hatched during the winter achieved larger mantle lengths (ML) and exhibited faster growth. Favorable feeding and temperature conditions during the following summer and autumn months increased both their growth rates and reproductive ability. In contrast, cohorts that hatched during the summer showed slower ML growth due to the lower water temperatures during the winter and spring, which they experienced at approximately 180 d of age. Our results demonstrate that size and growth of the swordtip squid varies seasonally, suggesting that differences in the growth rates and size at maturity are related to variation in water temperature.