Study On The Relationship Between CPUE And Marine Environmental Factors Of Atlantic Bigeye Tuna

The Atlantic Ocean is one of the main tuna fishing grounds in the world’s oceans,and its tuna output is second only to the Pacific Ocean.It is also one of the main sea areas for tuna longline fishing in China.Bigeye tuna is the main target species of longline fishing.The study on the distribution of bigeye tuna fishery has positive significance for the development of Atlantic tuna fishery in China.Based on the fishery production data from 2017 to 2019 provided by Shanghai Dier Deepsea Fisheries Co.,LTD.,this paper calculated the monthly center of gravity of Atlantic bigeye tuna fishery based on the catch per unit fishing effort,and analyzed its monthly and annual change rules.Combined with the Marine environment data acquired by satellite remote sensing,artificial neural network model and generalized additive model were constructed to study the distribution of bigeye tuna fishery.The main results are as follows:1.Change of gravity centers of fishing ground,catch and CPUE distributionBigeye tuna catches of ships per month for statistical and CPUE,found on the whole,every year in January,February and march catches and CPUE than other months,March to May catches and CPUE decline gradually,from May to August catches and CPUE gradually rising,in September and October catches and CPUE of annual minimum,The catches and CPUE gradually increased from October to December,and CPUE was also higher in the months with higher catches and lower in the months with lower catches.In terms of spatial distribution,the catch and CPUE of bigeye tuna in the northern hemisphere were higher than those in the southern hemisphere,and the catch and CPUE of bigeye tuna in the western Atlantic Ocean were higher than those in the eastern ocean.The areas with higher catch and CPUE of bigeye tuna were mainly located in 45°W～30°W and 5°N～10°N.In 2017,the gravity centers of bigeye tuna fishing ground moved southeast from January to May,and northwest from June to December.In 2018,the monthly gravity centers of bigeye tuna fishing ground moved west from January to July,and southeast from August to December.In 2019,the monthly gravity centers of bigeye tuna fishing ground moved northwest from January to May,northeast from June to October,and west from November and December.2.Study on the relationship between CPUE and environmental factors in bigeye tunaThe relationship between environmental factors and CPUE of bigeye tuna was analyzed by generalized additive model.Considering the comprehensive effect of all factors,longitude(with the highest deviation interpretation rate)had the most significant effect on Bigeye tuna CPUE,followed by month,salinity at 100m water depth,year,latitude,salinity at 200m water depth,chlorophyll concentration,sea surface salinity,sea surface temperature,water temperature at 50m water depth,salinity at 300m water depth.In the range of 24℃to 29℃,the CPUE of bigeye tuna increased with the increase of SEA surface temperature,and in the range of 26.8℃to 29℃,the CPUE of bigeye tuna decreased with the increase of sea surface temperature.The corresponding sea surface temperature range of bigeye tuna with higher CPUE was 26.0℃to 28.0℃.In the water depth and temperature range from 15.0℃to 27.0℃,the CPUE increases with the temperature rising,and the temperature range from 26.0℃to 27.0℃is the highest.In the range of 33.8‰～35.8‰sea surface salinity,the CPUE of bigeye tuna increased with the increase of salinity,and the sea surface salinity of higher CPUE ranged from 36.0‰to 36.5‰.In the salinity range of 100m water depth from 34.8‰to 37.2‰,the CPUE of bigeye tuna increased firstly and then decreased,and the salinity range of the higher CPUE of 100m water depth was 36.0‰to 36.5‰.In the range of 0.05～0.4mg/m3,the CPUE of bigeye tuna decreased with the increase of chlorophyll concentration,and in the range of 0.4～0.87mg/m~3,the CPUE increased with the increase of chlorophyll concentration,and the higher chlorophyll concentration range of bigeye tuna was 0.07～0.09mg/m~3.Neural network model was used to analyze the relationship between THE CPUE of big-eye tuna and Marine environmental factors.Month,longitude,salinity in 100m water depth,latitude,sea surface temperature,sea surface salinity,chlorophyll concentration and salinity in 50m water depth were taken as input layer factors,and the number of neurons in hidden layer was 10.The model with large-eye tuna CPUE as the output layer factor has the highest goodness of fit.The optimal model was used to analyze the influence weight of each explanatory variable on CPUE of bigeye tuna.The results showed that month had the most significant influence on CPUE of bigeye tuna,followed by longitude,salinity in 100m water depth,latitude,sea surface temperature,sea surface salinity,chlorophyll concentration and salinity in 50m water depth.The model predicts that the SST ranges from 23.5℃to 26.6℃in the area with higher CPUE for bigeye tuna.50m water depth and temperature range is15.6℃～20.8℃;The sea surface salinity ranges from 35.8‰to 36.9‰.The salinity of100m water depth ranges from 34.7‰to 35.8‰.Chlorophyll concentration ranged from0.58 to 0.9mg/m~3.Compared with the generalized additive model,the artificial neural network model has a limited ability to explain the relationship between THE CPUE of bigeye tuna and Marine environmental factors,so the generalized additive model is more suitable for analyzing the relationship between THE CPUE of bigeye tuna and Marine environmental factors.