Impacts Of The Climatic And Environmental Variations On The Spatio-temporal Distribution Of Potential Habitat Of Chub Mackerel Scomber Japonicus In The East China Sea And Yellow Sea

Chub mackerel(Scomber japonicus)is widely distributed in the Northwest Pacific Ocean,and this fish species is also abundant in the East China Sean and the Yellow Sea,it has highly ecological and economic values.At present,Scomber japonicus is the main fishing target for international fishing vessels from China,Japan and Korea,and other countries and regions.Scomber japonicus is a fish species performing seasonal migration behavior,therefore,the spatial distribution of fishing ground for chub mackerel is closely related to the migration route.As a short-lived fish species,the abundance an distribution of Scomber japonicus are strongly affected by the large/meso-scale climate variability and regional environmental variables at different spatial and temporal scales,the habitat and stock level of Scomber japonicus show significant interannual variability.Thus,developing an accurate habitat suitability index(HSI)model for Scomber japonicus and exploring the response of stock dynamics of Scomber japonicus to the climate changes are helpful to the sustainable exploitation and management of chub mackerel.Therefore,this study focused on the research concerning the HSI model,considered how to set the weighting and spatio-temporal scales for differnet environmental variables in the HSI model,evaluated the impacts of the ENSO(El Ni?o-Southern Oscillation)with various intensity and sea surface water temperature increasing in the global oceans on the habitat changes of Scomber japonicus,and finally developed the stock assessment model for Scomber japonicus inclusive with the climatic and environmental variables.The main conclusions are summarized as follows:(1)The weight setting of environmental factors in the HSI model for Scomber japonicus.The results indicated that the weight of the suitable HSI model in July should be case 5(the weight of sea surface temperature SST was 0.5,the weight of gradient of SST,GSST,was 0.25,the weight of sea surface height SSH was 0.25);the weight of the suitable HSI model in August should be case 6(the weight of SST was 0.8,the weight of GSST was 0.1,the weight of SSH was 0.1);the weight of the suitable HSI model in September should be case 1(the weight of SST was 0,the weight of GSST was 1,the weight of SSH was 0).In each month,the suitable HSI model was used to predict the habitat suitability index of Scomber japonicus on the fishing ground from July to September in 2012,and the HSI maps were overlapped with the actual fishery data.Results showed that the percentages of fishing efforts and catches in July accounted for85.78%and 92.55%,respectively;the percentages of fishing efforts and catches in August accounted for 76.74%and 86.69%,respectively;the percentages of fishing efforts and catches in September accounted for 51.83%and 56.11%,respectively.The findings in this study suggested that the weight-based HSI model could accurately predict habitat suitability for Scomber japonicus in the East China Sea and Yellow Sea.(2)The analysis of spatio-temporal scales of input parameters in the HSI model.Results suggested that the best spatio-temporal scale in the HSI model for Scomber japonicus in the coastal waters was that:month and 1°×1°.In the outputs of the HSI model with month and 1°×1°sclaes,the percentages of fishing efforts accounted for75.42%in the suitable habitat,and the percentages of fishing efforts accounted for12.93%in the poor habitat.The model performance of the HSI model with month and1°×1°sclaes was much better than those with other spatio-temporal scales.This HSI model also was applied to predict the habitat suitability of Scomber japonicus in 2012.Results indicated that the percentages of fishing efforts accounted for 60.89%in the areas with HSI>0.6,and the percentages of fishing efforts accounted for 13.88%in the areas with HSI<0.4.(3)The habitat changes of Scomber japonicus under the ENSO events with different intensity.The results suggested that the HSI model based on the arithmetic mean method could accurately predict the habitat suitability on the fishing ground of Scomber japonicus.Spatial correlation analysis suggested that significant positive relationship was found between the SST anomaly(SSTA)and the HSI of Scomber japonicus in space.While significant negative relationship was found between the SSH anomaly(SSHA)and the HSI on the fishing ground of Scomber japonicus in space.Different intensity of the El Ni?o and La Ni?a events has different impacts on Scomber japonicus stock:comparing to the moderate El Ni?o events(or moderate La Ni?a events),the very strong El Ni?o event(or strong La Ni?a event)would yield decreased SST anomaly(SSTA)(or increased SSTA)and elevated SSH anomaly(SSHA)(or reduced SSHA).The suitable habitat of Scomber japonicus would significantly decreased(or increased),leading to low CPUE(or high CPUE).(4)Spatial and temporal variability in the habitat distribution of Scomber japonicus under the SST changes in the global oceans.With the SST increased,the habitat of Scomber japonicus would clearly move northward,the changes of the percentage of the habitat areas for Scomber japonicus ranged from-73.1%to 44.7%.With the SST decreased,the habitat of Scomber japonicus would clearly move southward,the changes of the percentage of the habitat areas for Scomber japonicus ranged from-54.9%to123.4%.(5)Relationship between the net primary production(NPP)and the stock dynamics of Scomber japonicus.The results indicated that the catch,catch per unit effort(CPUE),longitudinal gravity centers of fishing effort(LONG)and latitudinal gravity centers of fishing effort(LATG)presented clearly seasonal and interannual variability.The NPP also exhibited different spatial distribution from July to September on the fishing ground of Scomber japonicus.The frequency distribution analysis suggested that the suitable range of the NPP for Scomber japonicus was 300-500 mg C/m~2/day in July,300-400 mg C/m~2/day in August,300-400 mg C/m~2/day in September,respectively.Correlation analysis indicated the CPUE of Scomber japonicus was significantly and positively correlated with the percentage of suitable range of NPP.Similarly,significant positive relationship was found between the average latitude of the suitable NPP and the LATG of Scomber japonicus.However,in the main fishing ground between 25~o-30~oN and 120~o-130~oE,negative relationship was found between the NPP and the CPUE of Scomber japonicus in space.Furthermore,the NPP level was different under different anomalous climate conditions on the fishing ground of Scomber japonicus.(6)Stock assessment of Scomber japonicus considering the climatic and environmental factors.The Pacific Decadal Oscillation index(PDO)was not correlated with the residual error of CPUE.However,the SST on the fishing ground of Scomber japonicus in June and the SSTA in the Ni?o 3.4 regions were highly related to the residual error of CPUE.Thus,the SST on the fishing ground of Scomber japonicus in June and the SSTA in the Ni?o 3.4 regions were included in the model for the stock assessment of Scomber japonicus.Results suggested that the performance of the model inclusive with the above-mentioned two factors was much better than other models.The findings in this study suggested that the SST on the fishing ground of Scomber japonicus in June and the SSTA in the Ni?o 3.4 regions could largely affect the stock level of Scomber japonicus in the East China Sea and Yellow Sea.The management of Scomber japonicus in the future should consider the climatic and environmental conditions,especially the SST on the fishing ground of Scomber japonicus in June and the SSTA in the Ni?o 3.4 regions.In conclusion,developing the HSI model for Scomber japonicus in the East China Sea and Yellow Sea should consider the weight setting and spatio-temporal scales of the fishery and environmental data in the model.Moreover,our findings suggested that the large-/meso-scale climate variability such as the ENSO events with different intensity and SST changes in the global oceans have produced large impacts on spatial and temporal distribution of the habitat of Scomber japonicus.The study on the stock assessment model for Scomber japonicus in the future should take the climatic and environmental conditions into account,such models inclusive with these factors can accurately predict the stock level of Scomber japonicus and help the scientific management of chub mackerel fishery.