Simulative analysis on results of summer closed fishing in the East China Sea with Ricker population dynamic pool model

The enforcement of the summer closed fishing in the East China Sea was declared by Chinese government in 1995 and the location for the closed fishing was 27°00′N-35°00′N with the duration from July 1 to August 31 per year.In 1998 the location was extended to 26°00′N-35°00′N and the duration was prolonged which was from June 16 to September 15 per year and the summer closed fishing area was extended to the South China Sea,the Yellow Sea and the Bohai Sea.The enforcement of the summer closed fishing has obtained obvious ecological,economical and social benefits and it is an important decision-making for sustainable fisheries development.In this paper the results of the three-month summer closed fishing(2001-2003) were analyzed by Ricker population dynamic pool model,based on a main commercial species-hairtail,Thichiurus japonicus,and revealed a rule between the conservation of hairtail stock and its utilization with combination of a different catchable age(t_(c)) and fishing mortality coefficient(F).The results indicated that it was necessary to carry out the summer closed fishing for the East China Sea under the case of a lower catchable age,a smaller mesh size and a larger fishing effort at present.If catchable age for hairtail was 0.5 year and annual fishing mortality coefficient was 1.5-3,its average annual biomass,catch and average individual body weight could be increased by 57%-104%,22.2%-32.2% and 32.5%-42.9%,respectively.However the biomass level,catch and average individual weight rooting in hairtail population was still lower and further reasonable utilization should be researched.If the catchable age is increased from 0.5 year to 1 year,the average annual biomass,catch and average individual weight will be increased by 173%-356%,72%-101% and 149%-187%,respectively.The fact is that the fishery resources are declining in the East China Sea and the TAC measure has not been enforced in China.We suggest the enforcement of summer closed fishing be continued,and catchable size and mesh size as the first management target be improved.[Journal of Fishery Sciences of China,2006,13(1):85-91]