The Relationship Between Temporal And Spatial Distribution Of Carangidae In The Northern China South Sea And Ocean Environmental Factors

Based on the production data of fishing vessels in the northern South China Sea from2010 to 2020,this paper selects data of Carangidae from trawlers（including otter trawl and twin trawl）and Seine vessels.And calculates the annual catch,annual catch proportion,annual CPUE and monthly CPUE of Carangidae in 11 years from the perspective of different fishing types.Combined with the fishing boat power analysis of Carangidae fish CPUE in different power segments of the change law,and the average CPUE under each classification level for significance analysis.Combined with environmental factors such as Sea Surface Temperature（SST）,Chlorophyll-a concentration（Chl-a）and Sea Surface Salinity（SSS）,Arc GIS software and GAM statistical method were used to analyze the spatial and temporal distribution of CPUE of Carangidae in the northern China South Sea and their relationship with ocean environmental factors.The main conclusions are as follows:By analyzing the CPUE changes of Carangidae in the northern South China Sea in terms of time factor,the following results are obtained:the CPUE of otter trawl increases first and then decreases gradually with the increase of years.The highest yield of Carangidae is 43.63×10⁴ kg in 2016,and the highest average CPUE is 0.88 kg·k W^-1·d^-1in 2016.The twin trawl the highest yield of 129.30×10⁴ kg in 2010,and the highest average CPUE is 4.36 kg·k W^-1·d^-1 in 2016.The highest yield of seine in 2016 was86.41×10⁴ kg,accounting for about 6.81%of the total output of seine,and the highest average CPUE was 3.61 kg·k W^-1·d^-1 in 2020.The fish yield and average annual CPUE of the three fishing types increased significantly in 2016.The variation of yield and the distribution of fishing grounds cause the CPUE of Carangidae to fluctuate greatly between years.The otter trawl had the highest average CPUE in August with an average CPUE of 0.78 kg·k W^-1·d^-1.The average CPUE of twin trawl in August and September were the highest,3.89 kg·k W^-1·d^-1 and 4.19 kg·k W^-1·d^-1,respectively.The seine had the highest average CPUE in September with an average CPUE of 3.40 kg·k W^-1·d^-1.The CPUE of the three types of operations in August showed the trend of CPUE _{twin trawl}>CPUE _seine>CPUE _{otter trawl}.The CPUE of the three types of operations increased first and then decreased with the change of seasons.Based on the Multifactor factor variance of different power segments,it can be seen that the CPUE of the three operation types increase first and then decrease with the increase of operation power.Under the same power segment,the CPUE of Carangidae present the situation that CPUE _{twin trawl}>CPUE _seine>CPUE _{otter trawl}.Seine vessels can use the phototaxis of Carangidae to catch them as the main fish,while the fishing performance of otter trawl vessels is weaker than the other two types of operation,making Carangidae only account for a small proportion in the total output of otter trawl.The analysis model based on GAM is:log（CPUE）～factor（type）+factor（season）+factor（year）+factor（month）+s（power）+s（lon）+s（lat）+s（SST）+s（SSS）+s（Chl-a）,this model can explain 42.1%of CPUE changes in Carangidae.The high-value fishing ground of Carangidae is mainly distributed in the east of Hainan Island in summer and autumn(110°E～112°E,18°N～21°N,SST 28.42～30.30℃,SSS 33.34～33.62,Chl-a 0.086～0.344mg·m^-3),Pearl River Estuary(112°E～114°E,21°N～23°N,SST 28.13～30.70℃,SSS33.57～33.44,Chl-a 0.101～7.536 mg·m^-3)and western Guangdong Sea(110°E～115°E,19°N～22°N,SST 27.64～30.33°C,SSS 33.01～33.65,Chl-a 0.094～6.958 mg·m^-3);The high-value fishing CPUE of twin trawl and seine vessels were mostly distributed in the Pearl River Estuary（112°E～114°E,21°N～23°N）,and the high-value fishing rates of Seine vessels were mostly distributed in the eastern part of Hainan Island（110°E～112°E,18°N～20°N）.In the western sea area of Hainan(106°E～108°E,18°N～20°N,SST29.11～30.52℃,SSS29.11～30.52,Chl-a 0.155～0.337 mg·m^-3),there were high value fisheries only in summer and autumn,which showed obvious seasonal variation.The northeast monsoon and Kuroshio in winter and spring increase the salinity of the waters from eastern Guangdong in the north of the South China Sea to the eastern part of Hainan Island,leading to the migration of most Carangidae fish to the coastal high-value fishing ground.The high temperature and low salt environment in summer increases the chlorophyll-a concentration in the northern part of the South China Sea,which provides suitable growing environment and rich bait for the growth of Carangidae in the waters from the west of Guangdong to the eastern part of Hainan Island,making high-value fishing grounds for Carangidae generally appear in the northern part of the South China Sea in summer.In the Taiwan Strait,some Carangidae fish migrate southward over winter,leading to a large amount of resources in fishing grounds in eastern Guangdong.