Analysis Of Biological Characteristics Of Portunus Trituberculatus And The Determination Of Releasing Capacity

According to the samples of Portunus.trituberculatus collected from Zhoushan fishing ground,Zhouwai fishing ground and Yueqing sea area,during May 2015 and May 2016,we studied the biological characteristics of P.trituberculatus,and compared the results with previous research.We also calculated the reasonable releasing capacity in Zhejiang province at present,and calculated the reasonable releasing number of P.trituberculatus larva under different exploitation rate.Totally 769 P.trituberculatus were collected,and the the carapace width ranged from 4.0cm to 20.2 cm,with the average value of 12.5 cm.The body weight ranged from 4.04g to 576.OOg,with average of 116.00g.The ratio of male and female was 1.28:1,female individuals were in the dominant position.The relationship between the body weight(W)and carapace width(L)was W?0.0644L2.9111.FIS AT II was used to estimate growth parameters L? and K,and the von-Bertalanffy growth equation was established,which is lt=21(1-e-0.83(t+0.373).Compared with the previous research results,the parameters a estimated in this research was larger,and b was litter smaller,but it was closer to 3.Its carapace length and carapace width were larger in this research than those in previous researches,the ratio was closer to the 1:2.The results showed that the individuals of P.trituberculatus are becoming younger and smaller.We used length catch curve method to estimate the coefficient of total mortality(Z),which equaled to 2.94y-1.The method of Rikhter&Efanov was used to estimate the coefficient of natural mortality(M),which was 1.707y-1.Through analyzing historical data,we determined the total resource of P.trituberculatus in Zhejiang sea areas during 1980s was not overfished,which was about 6.128×109.We used Baranov catches equation and resource exponential equation to determine the current resources of P.trituberculatus in Zhejiang sea area,which was about 4.556×109.So the reasonable releasing capacity of P.trituberculatus in Zhejiang province at present is about 1.572×109.The reasonable release number of P.trituberculatus for different exploitation rate showed polynomial trend,which was y=-1.025x2 +2.0438x +5.2113,with R2=0.9986.The results of this research can help researchers to scientifically carry out the stock enhancement of P.trituberculatus,and this method can also be applied to other species.It can provide technical support for the effect evaluation of fisheries resources enhancement and the establishment of corresponding standards in our country.