Dynamic analysis of fishery biology resources of trawl in waters of the Yangtze River Estuary

The paper analyzed variety status of fishery species and dominant species in trawl production based on data of trawl production and biology measuration in waters of the Yangtze River Estuary in 1990's. The result indicated percentage of Fishes was beyond 92%, Cephalopods and Crustaceans' percentage were very little, under 8% and 1% respectively, in trawl production of waters of the Yangtze River Estuary in 1990's. The number of species was always about 40 in each period. There were obvious changes in the number of species in different seasons of the same period and different periods of the same season. As the time passed, there were some changes of dominant species composition in trawl catches of waters of the Yangtze River Estuary. From early to late, most traditional dominant species were comparatively stable. However, there was a great fluctuation or sharply decrease in percentage of catch for some traditional dominant species, and small and low-quality fishes increased in percentage of catching and number of species. Analysis of body length structure of Trichiurus japonicus and Larimichthys polyactis revealed that there obviously had been a trend of miniaturization of stock since 1980's, the current miniaturization is very serious, but there was little change in body length structure of Setipinna taty. The varieties of composition and body length structure of dominant species were correlative with the gradual increased catching effort and change of environment of the water area.