Habitat Simulation Of Different Groups Of Skipjack Tuna In The Western And Central Pacific Ocean Based On MaxEnt

According to the Western and Central Pacific Fisheries Commission 2021 Tuna Fishery Yearbook,global catch data for major tuna species indicate that bonito will account for about 56%of the total global catch in 2021 and is the most important fishery for tuna purse seine fisheries.target.The bait organisms that tuna species feed on are scattered,and in order to find the bait with dynamic changes in location,they need to migrate quickly and gather into groups,and according to the differences in group characteristics,tuna groups are often divided into attached groups,such as driftwood groups and FAD attached groups and non-attached groups,such as free groups.Among them,the FAD schools are more stable and have higher casting success rate,and are widely used in purse seine fisheries.However,the extensive use of FAD leads to artificial changes in the physical environment of the sea surface,and bycatching too many juvenile tuna species,which will have serious negative impacts on the population health and pelagic ecosystem of the target species.For this reason,WCPFC began to implement closed season measures and require the purchase of operating days in 2008,with a view to guiding purse seine fisheries to free stocks.However,free stocks are faster moving and harder to catch,which can lead to higher fishing costs,while driftwood stocks are stable and easier to catch than free stocks.In the past,we mainly studied the bonito schools in a whole area,which caused the error in matching the spatial data with the environmental data,and some studies mainly studied the FAD with the attached schools and free schools,although they differentiated the fish groups.Most of these studies are limited to the surface environmental factors of the ocean,such as sea surface temperature,chlorophyll a concentration,and sea surface salinity,and rarely include vertical environmental factors into the habitat modeling consideration,which may affect the prediction performance of the model.On the other hand,there are almost no comparative studies at home and abroad for these three fish groups of bonito in different pelagic habitat preferences at the same time.Therefore,it is necessary to specifically study the habitat preferences and fitness zone distribution characteristics of the free,driftwood,and FAD-associated groups of bonito according to the group sex distinction.In this study,monthly tuna purse seine fishery production data from WCPFC statistics from 2016-2020 were used to filter sea surface temperature（SST）,sea surface salinity（SSS）,surface dissolved oxygen concentration（DO₀）,east-west current velocity（EV）,north-south current velocity（NV）,mixed layer depth（MLD）,surface chlorophyll a concentration（CHL₀）,dissolved oxygen concentration(DO₅₀)and chlorophyll a concentration(CHL₅₀)in the 50 m water layer,chlorophyll a concentration(CHL₁₀₀)in the 100 m water layer,water temperature（Temp200）,dissolved oxygen concentration(DO₂₀₀)and chlorophyll a concentration(CHL₂₀₀)in the 200 m water layer.a concentration(CHL₂₀₀)in a total of 13 environmental variables.Max Ent was used to simulate the distribution of habitat suitability and its monthly variation pattern for different groups of bonito,analyze the environmental preferences of different groups of bonito in the western and central Pacific Ocean and the suitable range of marine environmental factors,and explore the range of habitat suitability for the same group The distribution characteristics of different habitats were compared.The results show that:（1）the model evaluation indexes of different cluster sexes all exhibit high performance:the mean value of AUC in the training set of driftwood cluster is greater than 0.985,which is much higher than other cluster sexes,followed by FAD with attached cluster,and the variation of AUC value in the training set of FAD with attached cluster is significantly higher than other cluster sexes.the mean value of AUC in the test set of FAD with attached cluster is greater than 0.975,which is higher than other cluster sexes,and the difference between free cluster and FAD with attached cluster is not significant The variation of AUC value in the test set of driftwood group was higher than that of other groups.The mean value of sensitivity of driftwood group was greater than 0.940,which was higher than other groups.The mean value of TSS of driftwood group was greater than 0.880,which was much higher than that of other groups,and the difference between free group and FAD with attached group was not significant.The results of the evaluation indexes of each model were better than those of the stochastic model,indicating that the model has strong predictive ability and can be used for habitat suitability simulation of different group sexes of boobies in the western and central Pacific Ocean.（2）The preference of environmental factors differed among different group sexes of bonito:through the contribution rate and replacement importance value percentages of different fish groups,and combined with the output of the knife-cut method,the comprehensive analysis concluded that the dominant factors affecting the distribution of the fitness zone of the free group were SST,DO₂₀₀ and CHL₅₀ in order,the dominant factors affecting the distribution of the fitness zone of the driftwood group were SST,DO₀ and CHL₂₀₀ in order,and the dominant factors affecting the Overall,SST was the most important environmental factor for the three species,and dissolved oxygen and chlorophyll a concentrations would also limit the distribution of fish fitness zones to a certain extent.（3）Different groupings of bonito have different degrees of tolerance to environmental factors:when SST is below 28°C,the occurrence probability of bonito in 2016-2020 is generally lower than 0.2,indicating that bonito has difficulty inhabiting in waters with surface temperatures below 28°C.The response of different groups to the high habitat zone is basically the same,and their optimal SST range is30～31°C.The dissolved oxygen concentration in the 200 m water layer is quite important to the distribution of bonito free group and FAD accompanying group,and the two behave similarly in terms of dissolved oxygen tolerance threshold,which is too low(less than 50 mmol.m^-3)or too high(more than 200 mmol.m^-3)to restrict the distribution of bonito.For the driftwood group,the surface dissolved oxygen has the greatest constraint on its distribution,different from the dissolved oxygen tolerance threshold of the free and FAD-following groups,the environment is not suitable for bonito to survive at the surface when it is less than 160 mmol.m^-3,and the bonito under the driftwood group shows a high demand for oxygen when the dissolved oxygen is higher than 195 mmol.m^-3.The free group and the FAD with the attached group maintained the same degree of CHL tolerance to the 50 m water layer,with the optimum range of 0.10～0.30 mg.m^-3,while the bonito driftwood group preferred the200 m CHL,with the optimum range of only 0.025～0.0075 mg.m^-3.（4）The distribution range of high fitness of different groups of bonito was different:the high fitness zone of the free group rarely spanned longitude The high fitness zone is concentrated in the longitude range from 140°E to 175°W,and always in the latitude range from 8°N～10°S;the high fitness zone of the free group is widely distributed and will change significantly in the east-west and north-south directions,and will eventually be concentrated in the sea near Papua New Guinea and Solomon Islands.The high fitness zone of the driftwood group also rarely crosses 180°E in longitude and extends as far as 175°W.The high fitness zone is concentrated in the longitude range from 140°E～175°W and always in the latitude range from 10°N～11°S.The high fitness zone of the driftwood group has a relatively small distribution range and moves slightly weaker in the east-west direction,but moves more obviously in the north-south direction and eventually moves away from the The high fitness area of the FAD Followers Group also rarely crosses 180°E in longitude and extends as far as 172°W.The high fitness area is concentrated in the longitude range of 145°E～167°W and always in the latitude range of 4°N～8°S.The distribution of the high fitness area of the FAD Followers Group is not very different from that of the Driftwood Group in terms of area.However,it moves weakly in the east-west direction and not obviously in the north-south direction,and will eventually move away from Solomon Islands and Papua New Guinea waters along the equator.In this study,the free group,driftwood group and FAD accompanying group of skipjack tuna in the central and western Pacific Ocean were used as the research objects,and an attempt was made to determine the variation patterns of environmental factor preferences and distribution characteristics affecting their habitat suitability using the Max Ent model,aiming to provide a reference for the Chinese tuna purse seine fleet to accurately predict the central fishing grounds of skipjack tuna in this area,and to improve fishing efficiency to reduce the investment in fishing costs.At present,this study only selected common environmental factors for modeling analysis based on related studies,and it is suggested to include more environmental variables with potential effects for modeling in the future,such as thermocline depth,eddy kinetic energy and other factors.In addition,although this study revealed the habitat environmental preferences and suitability patterns of different groupings,the extensive use of FAD in the western and central Pacific Ocean has artificially altered the habitat environment of the surface layer of the ocean,which can cause significant disturbance to the habitat selection of boobies,which needs to be further analyzed in future studies.