Study On The Impacts Of Climate Change On The Potential Suitable Habitat Of Major Commercial Fish In Offshore China

Under the background of climate warming,marine environment changes significantly,affects the stability of fishery resources and ecosystem in our coastal areas.Various stages of fish life history(such as spatial distribution of different developmental stages,egg survival rate)and biological characteristics(such as growth rate,age at sexual maturity)are affected by climate change,altering species composition and distribution patterns.In recent decades,the Species distribution model(SDM)has become an important tool for studying the impact of climate change on the potential distribution of Species.In this study,8 species of Chinese offshore economic fish were selected for study.3pelagic fish species were included,namely the warm-temperate Scomberomorus Niphonius,Engraulis Japonius and warm-water Decapterus Maruadsi.There are also 5species of demersal fish,namely the warm-temperate Trichiurus Lepturus and Larimichthys Polyactis,the warm-water Navodon Xanthopterus,and the cold-temperate Gadus Macrocephalus and Ammodytes Personatus.These species occupy a very important position in the fishery resources.Therefore,it is important to predict the potential suitable habitats for the major economic fish species in our coastal waters and to assess the impact of climate change on their distribution.This will provide a basis for improving our adaptive capacity to cope with climate change.This study is based on the Biomod2 ensemble model on the R language platform,using environmental variables under current and future climate scenarios mentioned by the Intergovernmental Panel on Climate Change(IPCC)in the Fifth Assessment Report,The potential distribution areas of species in different seasons in the coastal areas of China during 2040-2050 and 2090-2100 under the climate scenarios of RCP4.5 and RCP8.5.9 single models were selected from the “Biomod2” package to build the ensemble model,and 8 single models were selected for the final weighted build.The weighting is based on the accuracy index true skill statistics(TSS)of the single model,and the accuracy evaluation index is the area under the subject’s operating characteristic curve(AUC value)and TSS value.The 9 single models are generalized linear model(GLM),advanced regression tree(GBM),generalized additive model(GAM),classification tree analysis(CTA),artificial neural network model(ANN),surface distributed compartment model(SRE),flexible discriminant analysis(FDA),random forest(RF)and maximum entropy model(MAXENT).Finally,the prediction results are visualized.And the change rate and centroid are calculated.In addition,in order to study the temperature sensitivity of species,we also predicted habitat changes after a uniform increase in summer SST.The main results of this paper are as follows:(1)Accuracy of ensemble distribution model: The accuracy of the four seasons model is high,but the environmental input data of the spring species model is average.Therefore,AUC values and TSS values of spring model were used as evaluation indexes to evaluate the accuracy of single model and ensemble model for 8 economic species.The results showed that the optimal single model was different for different species,but the accuracy of the ensemble model was higher than that of the optimal single model.The SRE model was removed from the combined model because the TSS value was less than0.8.(2)Changes in the potential distribution area of pelagic fish: S.niphonius and E.japonius decreased significantly with the passage of climate scenarios and years,while D.maruadsi showed an increasing trend,and the change was more obvious in summer than in other seasons.S.niphonius and E.japonius in 2050(RCP4.5),2100(RCP4.5),2050(RCP4.5)mainly decreased along the line from Okinawa to Taiwan Strait in spring,autumn and winter,and decreased in the south of the East China Sea in summer.In the spring,autumn and winter of 2100(RCP8.5),the main distribution areas were near Haizhou Bay,the line between Okinawa island and Taiwan Strait and the northern coastal waters of the South China Sea,and the whole distribution area was severely reduced in summer.In 2050(RCP4.5)and 2100(RCP4.5),D.maruadsi mainly increased in the offshore waters of the southern margin of the Yellow Sea in spring and autumn.The increase area is mainly in the southern part of the Yellow Sea in summer and the northern margin of the East China Sea in autumn.2050(RCP8.5)increase area similar to 2050(RCP4.5).For 2100(RCP8.5),the increase area in spring and autumn is mainly in the southern part of the East China Sea.The increase is mainly in the Bohai sea and the Yellow Sea in summer,and is expected to be in the northern east China Sea in winter.2100(RCP8.5)increases area expansion to higher latitudes compared to 2050(RCP4.5).(3)Changes in the potential distribution area of bottom fishes: The potential distribution of T.lepturus showed a decreasing trend in the summer of the future climate scenarios and winter of 2050(RCP8.5)and four seasons of 2100(RCP8.5).The other scenarios show a slight increasing trend in spring,autumn and winter,with an average increase of about 3.7% in spring,all about 1.2% in autumn and less than 1% in winter.The main distribution of decline for T.lepturus in spring,autumn and winter are all along the line from the Ryukyu Islands to the Taiwan Strait,with 2100(RCP8.5)declines extending to higher latitudes.The main decreasing range in summer is the southern East China Sea and northern South China Sea,with a significant overall decrease at 2100(RCP8.5).The increasing distribution in spring is in Bohai Bay,Laizhou Bay and the northern Yellow Sea,in autumn in the northern Yellow Sea and in winter along the central Yellow Sea.The distribution of L.polyactis decreased as a whole,and decreased unevenly with the passage of climate scenarios and years.The decrease rate was about10.78%～39.76% in spring,15.19%～21.79% in summer,6.27%～27.15% in autumn and7.27%～17.98% in winter.The main areas of decline in L.polyactis were in the vicinity of Haeju Bay and along the Korean Peninsula through the Ryukyu Islands to the Taiwan Strait and in the northern South China Sea,with 2100(RCP 8.5)declines extending to higher latitudes.In contrast,there was a slight increase in the Liaodong Peninsula.N.xanthopterus showed an overall increasing trend,with a higher increase rate in summer than in other seasons.In spring,autumn and winter,the distribution area is mainly increased in the east China Sea and the eastern part of the southern Yellow Sea in summer.G.Macrocephalus distribution showed a slight increase in spring and summer,and a decrease in winter.The average increase rate in spring was 4.48%,the average increase rate in summer was-2.7%,and the average decrease rate in winter was 15.1%.G.Macrocephalus did not change significantly in the whole distribution area,and the main decreasing area was the coastal line of the Yellow Sea,and the decrease of 2100(RCP8.5)was relatively significant.The distribution of A.personatus decreased in spring,summer,and autumn,and decreased unevenly with the passage of years and scenarios.The average decrease rate was about 26% in spring,18.8% in summer,27.7% in autumn and5.3% in winter.A.Personatus in spring,summer and autumn under future climate scenarios are mainly distributed in the bohai Sea and the coastal areas of the Yellow Sea,and the offshore areas in the southern part of the Yellow Sea tend to increase in winter.(4)The barycenter shift of pelagic fish and pelagic fish: the barycenter of species distribution showed a trend of moving to higher latitudes,and the shift to higher latitudes became more significant with the passage of climate scenarios and years.A.personatus had A tendency to move to lower latitudes in summer and autumn,and G.macrocephalus had A tendency to move to lower latitudes in winter.The barycenter of species distribution changed the most in summer,especially in 2100(RCP8.5),while the barycenter changed little in winter.On the whole,the species distribution model performed well in predicting the distribution area of different species.Temperature is an important factor affecting the seasonal variation of the distribution area,and depth is an important factor affecting the suitability of the distribution area.Pelagic fish and bottom fish showed different degrees of vulnerability to climate change,with the most significant change in summer and relatively small change in autumn.and the distribution area of S.niphonius and E.japonius decreased most obviously,especially in summer.T.lepturus and L.polyactis were the second most common,and the decrease was obvious from Ryukyu Islands to the west of Taiwan Strait.The overall distribution area of A.personatu and G.macrocephalus was not significantly reduced,but the distribution area of coastal waters was significantly reduced.D.maruadsi and N.xanthopterus are increasing,and the suitable distribution area in the East China Sea will increase.The distribution center of species will shift to the north,and the distribution area in the northern Yellow Sea will be more concentrated.The prediction results of summer temperature sensitivity show that the distribution changes significantly when the temperature rises 1.0℃ ～ 1.2℃.This study provides a trend analysis of fishery resource changes under the background of climate change,and provides a reference for fishery management and utilization under the background of climate change.