Longline Fishery Ground For Albacore Tuna In Solomon Islands Based On Marine Environmental Factors

Albacore tuna(Thunnus alalunga)is an important part of the tuna fishery resources,which is one of the major target species in longline fishing in the remote ocean fishery.Solomon Islands waters are located in the Pacific Ocean,which is the largest tuna fishing area in the world.In addition,albacore tuna is abundant in this sea area and carries high economic value.Albacore tuna is a highly migratory fish,and the formation of its fishing site is closely related to marine environmental factors.Therefore,it is necessary to grasp the mechanism of marine environmental factors on the formation and distribution of the center of gravity of albacore tuna fishery,which can provide a basis for the assessment of albacore tuna resource abundance and fishing forecast.,At the same time,the goal of sustainable development and improved productivity can be achieved.Based on the fishery data of 10 longline vessels in the waters of Solomon Islands,Central and Western Pacific Ocean from 2019 to 2021,the monthly center of gravity of alba tuna fishery was calculated according to the unit fishing effort and catch,and the monthly and interannual variation rules were analyzed.At the same time,combined with the Marine environmental data of the same period,the significance test of environmental factors on albacore tuna CPUE was explored through the generalized additive model(GAM),and the significant environmental factors were screened out according to the results of the model.Random forest model(RF)was used to analyze the weight changes of environmental factors in different seasons,and then explore the influence mechanism of environmental factors on albacore tuna fishery distribution in different seasons.By constructing and analyzing the SI model of the key environmental factors,the appropriate range of the key environmental factors in albacore tuna fishery was obtained.Different weights were assigned to different environmental factors,and the comprehensive habitat index model(HSI)with different weight schemes was established.The optimal HSI model was obtained by comparison and statistics.We used the data of 2021 to verify the optimal HSI model,and the software Arcgis10.8 was used for visual spatial overlay analysis.In order to provide a more scientific basis for rational development and production management of albacore tuna resources in Solomon Islands,this paper discusses its applicability in the analysis of albacore tuna fisheries in Solomon Islands waters.The results are as follows:(1)The analysis of the relationship between albacore tuna catch and fishing effort in Solomon Islands shows that the distribution of fishing ground is increasing in the southward direction,and fishing effort and catch are also increasing,and there is a high degree of similarity in the spatial variation of the two trends.From 2019 to 2021,the center of gravity of albacore tuna fishery in Solomon Islands was mainly distributed in the sea areas of 12°S-15°S,160°E-173°E.Through spatio-temporal analysis and comparison,it is found that the center of gravity of fishery in February to June of 2019 to2020 is shifted to the northeast,and the deviation range of each month is small,while the deviation range of June to December is large.The center of gravity of fishery in January has no obvious change with the change of year.In 2021,the center of gravity of the fishery is relatively concentrated in each month,except for October and December,the center of gravity of the fishery is within the range of 12°S-14°30’S,160°E-165°E.(2)Study on the relationship between CPUE of albacore tuna and temporal and spatial factors and Marine environmental factors based on generalized additive model(GAM).The results of the model show that CPUE will be affected by year,month,longitude and latitude,sea surface temperature(SST),mixed layer depth(MLD),chlorophyll a concentration(Chl-a),sea surface salinity(SSS),sea surface height(SSH),and dissolved oxygen concentration(DO).In order of influence on fisheries from large to small,latitude,month,chlorophyll a concentration,sea surface temperature,sea surface salinity,sea surface height,dissolved oxygen concentration,longitude,depth of mixed layer.(3)Through the results of random forest model,it is found that the influence weights of sea surface temperature(SST),chlorophyll a concentration(Chl-a)and sea surface salinity(SSS)change with the seasons.Among the three key environmental factors,sea surface salinity has the least influence weight,and chlorophyll a concentration has the most influence weight on albacore tuna fishery distribution in autumn.During the rest of the season,sea surface temperature had the greatest influence on albacore tuna fishery distribution.(4)The SI fitting curves of chlorophyll a concentration(Chl-a),sea surface salinity(SSS)and sea surface temperature(SST)basically conform to normal distribution with high fitting degree by using the single factor SI modeling of different months.The distribution range of each environmental factor can be obtained by fitting the curve,in which the distribution range of Chl-a is 0.01-0.15 mg/m~3,and the suitable range of fishery is 0.6-0.8 mg/m~3.The distribution of SST ranges from 26℃to 32℃.The optimum temperature of the fishery is higher in summer and autumn,ranging from 29℃to 30℃,and lower in autumn and winter,ranging from 27.0℃to 28.5℃.At the same time,SSS had the same trend of seasonal variation as SST,and the distribution range was 34.0-35.0,and the suitable range of fishery was 34.1-34.7.(5)Different weights were assigned to SST,Chl-a and SSS by weighted geometric mean method to establish a comprehensive HSI model.On the whole,when the weight coefficients of SST,Chl-a and SSS are 0.8,0.1 and 0.1 respectively,the accuracy of HSI model is the highest.According to the statistical verification results of fishing effort with HSI value greater than 0.6 in 2021,the proportions of fishing effort with HSI value greater than 0.6 in the four seasons were 62.27%,71.96%,69.33%and 61.60%,respectively.Based on the Arcgis10.8 software,the HSI value of each month was used as the base map to superposition the fishing effort of each month in 2021.The results showed that except for December and February,the fishing ground with high fishing effort in other months basically coincided with the sea area with high HSI value.It shows that the HSI model can better analyze the distribution of albacore tuna central fisheries in Solomon Islands.