Spatial-temporal Distribution Of Skipjack Tuna Fishing Grounds In Mauritania Waters And Its Relationship With Marine Environmental Factors

Katsuwonus pelamis,as a pelagic fish,occupies a large proportion in the pelagic fishery resources in the waters of Mauritania.Compared with other pelagic fishes,such as sardines,mackerel,horsemackerel,Skipjack tuna has a higher economy value.According to statistics,although the proportion of Atlantic catfish in the global Skipjack tuna is not high,judging from the production in the past years,the catch of the Atlantic Skipjack tuna has been increasing year by year.Beginning in the 1950 s,foreign fleets entered the waters of Mauritania to carry out fishing.China's offshore fishery business in this area started relatively late,and the fishing equipment and fishing technology of foreign fleets are ahead of our fleet.In addition,due to the over-exploitation and illegal fishing of various countries,the marine fishery biological resources in the Mauritania Sea area are declining.As a result,the Maota government has introduced a series of corresponding measures to limit the damage caused by excessive fishing efforts,such as increasing fishing Thresholds,limiting the number of bottom trawlers,increasing taxes,implementing a quota system,etc.In addition,factors such as the abundance and distribution of resources caused by climate change,the increase in other fishing costs,a series of problems in production operations,and other factors have made China's fishery enterprises face severe challenges in the development of Mauritania.In order to allow Chinese fishery enterprises to continue to develop in the waters of Mauritania,it is feasible to shift the focus of fishery development to middle and upper tier fisheries.Therefore,it is very important to analyze and compare the sturgeon fishery resources and fishing grounds in Mauritania.This article is based on the actual production data of Hongdong International(Mauritania)Fishery Development Co.,Ltd.'s double trawling operation fleet from 2017 to 2019.Based on the data of four marine environmental factors: sea surface temperature(SST),chlorophyll a concentration(Chl-a),sea surface salinity(SSS),and sea surface height(SSH),the spatial and temporal distribution of the sturgeon fishery in the sea of Mauritania and its relationship with the ocean The relationship between environmental factors is studied.The main conclusions are as follows:(1)Analysis of the change of CPUE of the Skipjack tuna fishery fishing ground in the waters of Mauritania in the time series shows that: Mauritanian Skipjack tuna can be caught all year round.After averaging the same months in the three years from 2017 to 2019,and analyzing the average output and average CPUE distribution of each month,the months with the highest production of Skipjack tuna fisheries were December,January and July,August.It can be preliminarily estimated that the fish flood season of the Skipjack tuna fishery in the waters of Mauritania is mainly concentrated in December,January,July,and August.(2)Analysis of the change of CPUE of the Skipjack tuna fishing ground in the sea area of Mauritania in the spatial sequence: As long as the Skipjack tuna fishing ground is concentrated in the northern fishing ground,that is,the sea area north of 19 °.(3)By analyzing the relationship between the CPUE and sea surface temperature of the Skipjack tuna fishery in the waters of Mauritania,it is concluded that there are mainly two temperature sections in the sea area where the high CPUE is located,namely 17 ° C-20 ° C and 22 ° C-24 ° C.Among them,17 ?-20 ? is the optimal SST in December and January,22 ?-24 ? is the optimal SST in July and August,and the SST in the sea area where the higher CPUE is different every month.(4)After analyzing the relationship between CPUE and chlorophyll a concentration in the Skipjack tuna fishery in Mauritania,it is concluded that the CPUE points of the Skipjack tuna fishery are mainly concentrated in the range of chlorophyll a concentration of 0.2-6.5 mg/m3,but the concentration of chlorophyll a on the CPUE The effect of the distribution is not significant.(5)By analyzing the relationship between the CPUE and SSS of the Skipjack tuna fishery in the waters of Mauritania,it is concluded that the environmental factor Caspian surface salinity SSS has the least impact on the Skipjack tuna CPUE.The CPUE is mainly distributed in the SSS range of 32-36.7,which is the most suitable.The SSS is 35.9-36.7.Because of its small interpretation rate,it is not possible to determine the Skipjack tuna fishing grounds from the distribution of sea surface salinity.(6)By analyzing the relationship between CPUE and SSH of the Skipjack tuna fishery in the waters of Mauritania,it is concluded that the impact of SSH on sturgeon is mainly in the range of-0.05 to 0.1.The optimal SSH for Skipjack tuna in Mauritania is 0.03-0.04.(7)By using GAM model analysis,the spatial and temporal factors(year,month,latitude,longitude)and marine environmental factors(SST,Chl-a,SSS,and SSH)in the Skipjack tuna fishing ground in the Mauritania sea area have an effect on the CPUE of the fishing ground.Studies have shown that among the various space-time factors,the month has the largest impact,followed by the latitude,and the year has the smallest impact.Among the various marine environmental factors,SST has the greatest impact on CPUE,followed by SSH,and SSS has the least impact.In order of importance,the impact factors are: month> SST> Lat> SSH> Chl-a> Lon> SSS> year.