Population Characteristics And Resource Assessment Of The Parent Crab Eriocheir Sinensis In The Yangtze Estuary

In this paper,the reproductive population of Eriocheir sinensis in the reproductive migration of the Yangtze Estuary was taken as the research object.Based on the population characteristics of Eriocheir sinensis in the Yangtze Estuary,the resources of Eriocheir sinensis in the Yangtze Estuary were estimated by different resource assessment methods,and the exploitation of Eriocheir sinensis in the Yangtze Estuary in recent years was analyzed by using the surplus production model.The purpose is to provide a scientific basis for the assessment of Eriocheir sinensis resources and fishery management in the Yangtze Estuary.1.Population characteristics of the parent crab Eriocheir sinensis in the Yangtze EstuaryBased on the survey data of Eriocheir sinensis in the Yangtze Estuary from 2015 to 2017,the population structure and reproductive characteristics of Eriocheir sinensis in the Yangtze Estuary were studied.The flood season peak of Eriocheir sinensis in Chongming Xitan mainly from mid-November to early December The flood season change of Chongming Dongtan and Hengsha Shoal is similar The peak mainly concentrates from late November to late December The flood season peak of Jiuduansha is mainly from mid-November to mid-December.The average daily single-net catch of Eriocheir sinensis in the Yangtze Estuary during the flood season from 2015 to 2017 was 2.71 kg,3.93 kg and 2.76 kg,respectively.The variation trend of CPUE and daily catch amount are the same in each flood season.The spatial distribution of the size of Eriocheir sinensis showed a downward trend from the North-South branch intersection of the Yangtze Estuary to the downstream.In the time distribution,the medium and small size Eriocheir sinensis accounted for a relatively high proportion in 2015-2017.In the flood season of 2015-2017,the ratio of male to female of Eriocheir sinensis was 0.60:1,0.46:1 and 0.49:1,respectively.From December 2017 to April 2018,ovigerous mitten crabs can be caught in Jiuduansha.In 2017,the relative fecundity of ovigerous mitten crab in Chongming Dongtan,Hengsha Shoal and Jiuduansha were(12.80 ± 4.14)× 102,(13.10 ± 6.25)× 102 and(7.82 ± 4.47)× 102 grain/g.2.Estimation of Eriocheir sinensis resources in the Yangtze Estuary based on different resource assessment methodsBased on the monitoring data of Eriocheir sinensis in the Yangtze Estuary in 2017,the resource amount of the reproductive population of Eriocheir sinensis in the Yangtze Estuary was estimated by means of marker recapture method,Leslie method,Delury method and fishing mortality coefficient method,respectively.The 2017 marked crab recapture investigation began on December 16 and ended on January 1,2018.The total catch of parent crabs of Eriocheir sinensis in the Yangtze Estuary was 23.88 t,including 11.49 t in Chongming Dongtan,3.89 t in Hengsha Shoal and 8.5 t in Jiuduansha.During the investigation period,234 marked crabs were caught in the Yangtze Estuary,including 75 in Chongming Dongtan,44 in Hengsha Shoal and 115 in Jiuduansha,with a recovery rate of 4.88%.According to the number of marking released and the number of final recapture,the population resources of Eriocheir sinensis in the Yangtze Estuary in 2017 were calculated by Lincoln index method,which was 489.34 t.By using the Leslie method,the linear regression between the catches per unit effort and the total catches was made,and the equation y=-0.0001x+46.606 was obtained(R2=0.148).The reproductive population resources of Eriocheir sinensis in the Yangtze Estuary in 2017 were 466.06 t.By using the Delury method,the linear regression between natural logarithm of catch per unit effort and accumulated fishing effort was made,and the equation y=-0.OOOlx+3.8437 was obtained(R2=0.2111).The reproductive population resources of Eriocheir sinensis in the Yangtze Estuary in 2017 were 466.98 t.According to the regression analysis of Leslie method and Delury method,the catchability coefficient is 0.001 and the fatality coefficient of parent crab fishing in flood season is 0.2754.The average resource of the breeding population of Eriocheir sinensis in the Yangtze Estuary in 2017 is 407.45 t.3.Estimation of parent crab exploitation rate and analysis of sustainable catches of Eriocheir sinensis in Yangtze EstuaryBased on the survey data of Eriocheir sinensis in the Yangtze Estuary in 2017,the flood season characteristics,exploitation rate,fishing mortality coefficient and maximum sustainable yield of the breeding population of Eriocheir sinensis in the Yangtze Estuary were analyzed by using Leslie method,Delury method and Schaefer model,respectively.During the fishing season from November 11 to December 27,2017,there were four recruitment stocks of parent crab Eriocheir sinensis in theYangtze Estuary.Among the four recruitment stocks,the fishing duration of each recruitment stock is different.The longest fishing duration is from 4 December to 16 December,totaling 13 days;the shortest is from 25 November to 27 November,only 3 days;the average is 6.75 days.The total resources of recruitment stock of Eriocheir sinensis in the Yangtze Estuary were estimated by Leslie method to be 250855.78 kg,with the exploitation rate ranging from 10.82%to 73.91%,with an average of 36.22%.The total resources of recruitment stock of Eriocheir sinensis were estimated to be 319 574.85 kg by Delury method.The exploitation rate ranged from 8.12%to 65.53%,with an average of 32.04%.The daily fishing mortality coefficients and average daily fishing mortality rates of Eriocheir sinensis supplementary population in the Yangtze Estuary in 2017 estimated by Leslie method and Delury method were 0.078 and 7.40%,0.070 and 6.68%,respectively.Based on the flood season monitoring data of the stations in the Yangtze Estuary from 2011 to 2017,the maximum sustainable yield of Eriocheir sinensis in Chongming Dongtan,Hengsha Shoal and Jiuduansha were 42140.31 kg(fMSY=1821.57),33487.76 kg(fMSY=1504.22)and 47608.91 kg(fMSY=1292.47),respectively,by linear regression using Schaefer model.Overall,the maximum sustainable yield of Eriocheir sinensis in the Yangtze Estuary from 2013 to 2017 was 124536.25 kg(fMSY=3349.55).The results show that the resources of Eriocheir sinensis in the Yangtze Estuary are in good condition,the fishery exploitation is optimistic,and there is no overfishing,which is conducive to the recovery of Eriocheir sinensis resources in the Yangtze Estuary.