The Dynamics And Assessment Of Two Kind Of Commercial Fishes Resources Of The East China Sea

The East China Sea is rich in marine fishery resources, with the higher economic value of yield and more types of large species. Its fishing yield accounts for a large proportion of marine fishing production of the whole country. Small yellow croaker and llisha elongate are important and main commercial fishes in The East China Sea. According to the catch data of small yellow croaker and llisha elongate, the use of V-B equation and ELEFAN Methods, their growth equations were established. Resources were also analyzed with B-H model. Results were as follows:The growth parameters of llisha elongate were estimated to be L_∞= 448.88mm, W_∞=1171.44g, K = 0.3889, t0 =- 0.2742. The growth equation in length can be expressed as L_t = 448.8 8(1-e^{-0. 3889(t+0.2742)}),the growth equation in weight can be expressed as W_t = 1171. 44(1-e^{-0. 3889(t+0.2742)})^2.6215. There was no inflection point in length growth, while the weight inflection point was 2.2039. At inflexion age, Ilisha elongate weight was 332.44g, the corresponding body length was 260.72mm, the total mortality coefficient was 1.7170, natural mortality coefficient was 0.4769 and the fishing mortality coefficient F = 1.2401.Using B-H model ,the average age, average length and average weight were calculated under different fishing mortality coefficient F, the results showed that: in the case of tc =1.93, F = 0.85, the catch can reach maximum, F <0.85, Ilisha elongate resources were underutilized. F> 0.85, Ilisha elongate resources were in the status of growth overfishing type .When F = 0.85, the catch per recruit can get Maximum at the first capture age of 2.13.tc < 2.13 ,the catch increased with the first capture age. This stage showed Ilisha elongate catch were in the stage of growth overfishing type. tc>2.13, the catch decreased with capture age. This period indicated that Ilisha elongate resources were underutilized. Comprehensive analysis, it is proposed that the optimal first capture age should be 2.33 and the fishing mortality coefficient F should be 0.95.The growth parameters of small yellow croaker were estimated to be L_∞= 283.50mm, W_∞= 327.47g, K = 0.300, t0 =- 0.498. The growth equation in length can be expressed as L_t = 283. 50(1-e^{-0. 300(t+0.498)}),the growth equation in weight can be expressed as W_t = 327. 47(1-e^{-0. 300(t+0.498)})^2.7792,the inflection point of growth weight was 2.91, the natural mortality coefficient was 0.3841, the fishing mortality coefficient was 1.63 and the total mortality coefficient 2.0141.Using B-H model ,the average age, average length and average weight were calculated under different fishing mortality coefficient F, the results showed: in the case of t_c =1.50, F = 0.7,the catch can reach maximum. F <0.7, small yellow croaker resources were underutilized. F>0.7 small yellow croaker resources were in the status of growth overfishing type. When F = 1.63, the catch per recruit can get Maximum at the first capture age of 3. tc < 3, the catch increased with the capture age. This stage showed small yellow croaker catch were in the status of growth overfishing type. tc>3, the catch decreased with the first capture age. This period indicated that small yellow croaker resources were underutilized. Comprehensive analysis, it was proposed that the optimal first capture age should be 2.25 and the fishing mortality coefficient F should be 1.3.The current llisha elongate fishing industry in East China Sea (F = 1.24, tc = 1.93 ) maked the llisha elongate resources be in over-fishing t status. Small yellow croaker fishing mortality coefficient (F> 2.0) also caused over-fishing.In order to protect llisha elongate and small yellow croaker resources ,we should gradually increase capture age by year and appropriately reduce the fishing intensity so as to resume and protect East China Sea resources better .