Study On The Stock Of Trichiurus Haumela In The Beibu Gulf

Located in the northwest of the South China Sea,the Beibu Gulf is rich in fishery stock.It is estimated that the existing stock of the Beibu Gulf are 16.9×10⁴ tons and 244species of fish,so it has become an excellent traditional fishing ground in China and one of the waters with the richest fishery stock in the northern part of the South China Sea.Trichiurus haumela is one of the main dominant species and economic fish in the area,as well as one of the most important fishing objects in the South China Sea,with important economic status.It is an important basis to ensure the sustainable development and utilization of hairtail fishery stock to evaluate the population parameters and stock status of T.haumela,understand the relationship between stock density and environment,and analyze the change characteristics of spatial aggregation and dispersion.Therefore,this paper based on the anal length data of T.haumela collected in the Beibu Gulf in 2006-2006 and data of T.haumela stock density collected in 2006-2018,based on the length-based Bayesian Biomass Estimation method（LBB）estimate population parameters and stock status of T.haumela in the Beibu Gulf using Generalized Additive Model（GAM）to explore the relationship between T.haumela stock density and environmental factors,and use Standard deviation Ellipse（SDE）to understand the spatial distribution characteristics of T.haumela and analyze the changes of spatial aggregation and dispersion.The main conclusions are as follows:（1）Spatial aggregation and dispersion of T.haumela in the Beibu Gulf.The spatial distribution pattern of T.haumela was plotted by SDE to analyze the interannual and seasonal changes of hairtail distribution and explore the change mechanism The results showed that the Beibu Gulf T.haumela stock density distribution phenomenon of agglomeration,year by year present southwest fishery distribution direction affected by the ocean floor Density of center of gravity in the southwest to the northeast,summer stock The northeast to move,winter stock density of center of gravity in the south The density center of hairtail stock in winter is more northeast than that in summer.In the spring Autumn as T.haumela major nesting season,density focus its stock in summer Winter T.haumela central fishing grounds.（2）Status of T.haumela stock in the Beibu Gulf.Using LBB to estimate the asymptotic long anal(L_inf)、the relative mortality（M/k and F/K）、the optimal opening anal length(L_copt)of T.haumela,and evaluate its stock status（B/B₀）In addition,length frequencies were reconstructed by different group distances to improve the accuracy of LBB model estimation.The results showed that the average L_infwas 44.4 cm,the average L_copt was 28.5 cm,and the average M/k and F/K mortality was 1.32,and 2.76,the fishing intensity（F/M）was 2.20,the exploitation rate（E）was 0.67,the average relative biomass（B/B₀）was 0.16,and the estimated population parameters and stock status of 1 cm group distance were closest to the average value by fitting the logic curve.The average minimum mature anal length of T.haumela was 28.63 cm.The results show that the population structure of T.haumela in the Beibu Gulf is simple and small due to the state of overexploitation.（3）Relationship between density of T.haumela and environment in the Beibu Gulf.GAM model was used to study the relationship between stock density of T.haumela,chlorophyll-a,sea surface water temperature anomaly,water depth,offshore distance,longitude and latitude.The results showed that the stock density of T.haumela was affected by the anomaly of water depth chlorophyll-a and sea surface water temperature,and the contribution rate of environment to stock density was 7.69%and 11.80%,respectively 14.50%and 16.20%,in which the cumulative deviation of generalized additive model to stock density is 16.2%.Results show that the Beibu Gulf T.haumela stock density drop year by year is the main cause of its spatial distribution gradually gathered Moreover chlorophyll-a T.haumela spatial distribution have a significant impact,but the depth of longitude and sea surface temperature anomaly value has no effect on its spatial distribution...