Statistical Study On Stock Dynamics Of Hairtail In The East China Sea And Yellow Sea

Hairtail Trichiurus lepturus is one of the main economic fish in China,it spreads from Hokkaido south coast to the East China Sea 、west coast of the Korean Peninsula、Bohai Sea and Yellow Sea.,and belongs to Japan Sea/East China Sea stock.In Japan,hairtail stock is mainly caught by large trawl fishery、large and medium-sized purse seine fishery、offshore trawl fishery in the East China Sea and Yellow Sea. Based on the yield and catch per unit effort(CPUE) data of Japan Sea/East China Sea stock collected by Japan Fisheries Agency from the year 1981 to 2009, statistical study on stock dynamics of hairtail Trichiurus lepturus in the East China Sea and Yellow Sea was done. In this study age-structured production model(ASPM) was mainly used to estimate the dynamics of stock size and stock biomass in the area,described the condition of stock dynamics and its development tendency. The results showed that the stock size kept decreasing from 1.7 numbers(1981) to 0.8 numbers(2009). As to the age classes, the stock size at age 4 to 8 decreased rapidly, from the year 1997 there were almost none older age classes. The stock biomass decreased rapidly from 70 thousand tons(1981) to less than 30 thousand tons(1985), and from the year 2003 the stock biomass maintained at a lower level, less than 10 percent of the year 1981. Parameter’s sensitivity analysis showed that the steepness h and natural mortality M had bigger impact on the model when compared to other parameters. When the value of M became smaller, the estimated stock size became smaller; When the value of h became bigger, the rate of decrement became smaller, this is because that the speed of recruitment became higher.