On Community Structure Of Crab And Biological Parameters And Stock Number Of Portunus Trituberculatus In Shandong Offshore

The Shandong offshore includes Laizhou Bay and southern Bohai Sea,the northern Shandong Peninsula and the southern Shandong Peninsula.Due to the injection of many rivers,light salt water is very abundant and the nutriment is rich.There are Southern Bohai Sea fishing grounds,Laizhou Bay fishing grounds,Yanwei fishing grounds and Qinghai fishing grounds,because which the coastal waters along Shandong Peninsula become the spawning and feeding ground for many important economic species.In recent years,because of overfishing and pollution,traditional fishery resources here are destroyed.As important economic species(such as Portunustrituberculatus and Charybdis japonica)and bait-type species(such as Charybdis bimaculata and Eucrate crenata),the community structure and diversity of crabs are of great significance for the fishery production and fishery ecology,however,only a handful of studies on Shandong Peninsula.Based on the data form surveyed in this area from 2014 to 2015 by bottom trawl,this paper analyzed the spatial and temporal distribution,structure community,dominant species,diversity and resource of crabs used the Shannon-Wiener index,Margalef species richness index,Pielo's evenness index,IRI and so on.Meanwhile,based on the data of seven bottom trawl surveys on Portunus trituberculatus form May 2012 to November 2012,the biological parameters and growth characteristics of Portunus trituberculatus were studied.We hoped this study could offer scientific basis and base data for sustainable development and multiplication release of crabs,especially the Portunus trituberculatus in the coastal waters along Shandong Peninsula.Based on the data form bottom trawl surveys in Shandong offshore from 2014 to 2015,the spatial and temporal distribution,structure community and dominant species for crabs were analyzed.Results showed that 20 kinds of crabs were captured during the four survey cruises,which belonged to 17 genera,10 families.Portunus trituberculatus and Charybdis japonica were the main economic species and the others were low-value species.Charybdis immaculate,Charybdis japonica and Portunus trituberculatus were the main dominant species.The seasonal variation of the dominant species was obvious.Biomass in Laizhou Bay southern Bohai Sea and the coastal waters along the southern Shandong Peninsula changed seasonally with the highest in summer and the lowest in winter,but no significant seasonal change occurred in the coastal waters along northern Shandong Peninsula.According to the data,the average Shannon-Wiener diversity index(H?),Margalef richness index(D)and Pielou evenness index(J')in survey waters were very low,which manifest that there was an lower-level diversity of crab in this waters.Result of CLUSTER analysis showed that water depth,water temperature and salinity were the main factors affecting the community structure.Through influenced the water temperature and salinity,the Bohai-Lai Longshore Current,the Yellow Sea Warm Current and the Huanghai Sea Cold Water Mass influenced the community structure.This paper showed that most of crabs in Shandong offshore were small,bait-type species.The crab diversity was very low.The dominant species varied obvious.The MI was very high.The results showed clearly that the crabs community structure were unstable.Based on the data of seven bottom trawl surveys on Portunus trituberculatus form May 2012 to November 2012,using FiSAT ? software,Growth,mortality and recruitment were studied.The results showed that 1128 Portunus trituberculatus were captured and the sex ratio was 0.96(female to male),from which we could see it was heading towards normality.The length of female Portunus trituberculatus ranged from 27 to 227 millimeters,the male ranged from 46 to 185 millimeters.According to determined data and using the Electronic Length Frequency Analysis?,we obtained the growth parameters of Portunus trituberculatus that were as follows: female Portunus trituberculatus: K=1.60,L?=241.50,W?=639.29,t0=0.081,male Portunus trituberculatus:K=1.50,L?=210.00,W?=418.23,t0=0.091.All of the parameters conformed to the growth characteristics of Portunus trituberculatus such as growth speed,short life cycle and ability to complement.Using the Length-Converted Catch Curve,Pauly Empirical Formula and Beverton and Holt Y/R Analysis module,we estimated the mortality,exploitation ratio and the optimum utilization rate of Portunus trituberculatus,the results were as follows: female Portunus trituberculatus: The total mortality(Z)was 4.17,the natural mortality(M)was 1.20,the mean selection length(Lc)was 62.38 millimeters,the fishing mortality(F)was 2.97,the exploitation rate(E)was 0.712 and the optimum utilization rate(Emax)was 0.515,male Portunus trituberculatus:The total mortality(Z)was 3.76,the natural mortality(M)was 1.19,the mean selection length(Lc)was 40.84 millimeters,the fishing mortality(F)was 2.57,the exploitation rate(E)was 0.684 and the optimum utilization rate(Emax)was 0.487.All of them could accord with the actual circumstance,which we could trust in and believe that there were seriously over developing.Research had shown that the sex ratio of Portunus trituberculatus in Laizhou bay was in a normal level,which meaned its growth in good condition;the exploitation ratio of Portunus trituberculatus was significantly higher than the normal level,overdeveloping occured in Portunus trituberculatus in Laizhou bay;the resources of Portunus trituberculatus was below the ecological capacity.The sweep-area method,design-based method and Length-Structured VPA method were applied separately in the fisheries stock assessment on Portunus trituberculatus in Laizhou Bay.The results showed that through the sweep-area method,the resources of Portunus trituberculatus in Laizhou Bay were 1204 t from summer of 2014 to spring of 2015;through the design-based method,the resources of Portunus trituberculatus in Laizhou Bay were 1499 t from summer of 2014 to spring of 2015;through the Length-Structured VPA method,the resources of Portunus trituberculatus in Laizhou Bay were 4611 t in 2012.This study showed the design-based method was more precise than the sweep-area method;the resource of Portunus trituberculatus was below the ecological capacity,there was still plenty of scope for progress.