Study On The Response Of Major Small Pelagic Fish Resource In The Northwest Pacific To Large Scale Climate-marine Environmental Changes

Small pelagic fishes are important fishery resource in the north pacific.They have the characteristics of short life cycle,fast growth rate and high clustering,etc.Their resources fluctuate significantly from year to year and were affected by climate-marine changes.In this paper,the characteristics of the key climate-marine index such as ENSO(El Ni?o/La Ni?a-Southern Oscillation),PDO(The Pacific Decadal Oscillation),KR-OY(Kuroshio-Oyashio)and it is influence on the changes of the habitat environment and resources of fish were assessed,focusing on three main small pelagic fishes,including saury(Coloabis saira),chub mackerel(Scomber japonicus),sardine(Sardina pilchardus).The climate-marine changes is direct influence on migration distribution and resource abundance of small pelagic fishes and indirect delayed influence on parental reproduction and spawning,larvae and juvenile survival rate,resource fluctuation were discussed.Combined with the results of(cross)correlation test,the Vector Autoregression model(VAR)was used to predict the catch of small pelagic fishes.The main results are as follows:1.By comparing the fluctuation trend of large-scale climate index,marine environment index and fish catches in the past 24 years,it is find that:(1)The fluctuation trend of the Pacific decadal oscillation index(PDOI)and ocean Ni?o index(ONI)is consistent,while the change direction of North Pacific gyre oscillation index(NPGOI)and southern oscillation index(SOI)is basically similar;(2)The Sea surface temperature(SST)annual fluctuation range of Kuroshio and Kuroshio extension area is small,which is suitable for the survival of juvenile fish that are easily affected by marine environmental changes and grow fragile.The SST of the Oyashio and Oyashio extension area fluctuates greatly,Strong flow exchange brings abundant nutrients and which suitable for mature fish to feed migration;(3)The sea surface temperature gradient(SSTG)values in the Kuroshio and Kuroshio extension areas of the Northwest Pacific Ocean are relatively small,while the SSTG values in the Oyashio-Kuroshio area are relatively high;(4)Compared with chub mackerel and sardine,saury resources fluctuated more sharply.2.At small time and space scales,the maximal lag correlation between the large-scale climate index and marine environment were analyzed,the results show that:(1)SOI has the strongest correlation with ONI,followed by PDOI.NPGOI has the most close correlation with PDOI,and their are correlated through ENSO in different stages of teleconnectation.The Arctic oscillation index(AOI)has not direct correlation with ONI and PDOI that representing sea surface temperature anomaly(SSTA)values in the short term;(2)The annual variation of SST and SSTG has not significant relationship with large-scale climate in the same year,while the monthly average large-scale climate has the maximum lag correlation with the marine environment index.When the SST lags the PDO event for 1-2 months,their correlation shows the maximum negative correlation.When the interval is 5-6 months,the correlation coefficient between SOI and SST-transition zone(SST-TZ)is the highest.The correlation between SSTG and PDO was the highest after 6-8 months,and the correlation coefficient between SOI and SSTG-transition zone(SST-TZ)was the highest when the interval was 8-10 months.There was no significant correlation between the temperature parameters of the Northwest Pacific Ocean and ONI,SOI,AOI.3.Based on the catch data of small pelagic fish in the Northwest Pacific Ocean from 1995 to 2018,the correlation between small pelagic fish catches and climate-ocean index fluctuation was explored by referring to the above cross correlation analysis method.(1)The maximum positive correlation between the catch and PDOI was lagged by-1,3-4 years;Chub mackerel catches lagged behind PDOI for 2-3 years and NPGOI for 4 years had the largest correlation;NPGOI had significant correlation with sardine catches,while PDOI had the greatest positive correlation with sardine catches lags of 5years;The average annual SOI and AOI had not significant correlation with the average annual resources of the main small pelagic fishes.(2)There have not significant correlation between spring climate index and small pelagic fishes.In summer,ONI and PDOI were significantly positively correlated with the resource of chub mackerel.In autumn and winter,NPGOI was significantly positively correlated with the resource of saury,and negatively correlated with the resource of chub mackerel and sardine.(3)Compared with SST,Chub mackerel resources has more significant with SSTG,and the catches of saury and sardine were significantly correlated with SST and SSTG respectively.(4)There was significant negative correlation between annual catches of saury and sardine,but no significant correlation between mackerel and sardine.4.In order to predict the annual trend of fish abundance relatively accurately,nine VAR models were constructed based on past empirical values and other variables in the same system to analyze the dynamic impact of climate abrupt change on the catch of small pelagic fish,for explaining the impact of various large-scale climate fluctuations on the catch formation.The result shows:(1)Variables with significant correlation meet the premise of VAR implementation-Pass ADF sequence stability.All the variables except NPGOI passed the co-integration test,indicating that there was a long-term stable relationship between the model variables.(2)According to the Granger causality test results with a maximum lag of 4,in addition to AOI,the early changes of Chub mackerel-total catches(CM-TC),ONI,SOI,PDOI and NPGOI all have a significant impact on the late Japanese sardine-total catches(JS-TC).The early changes of JS-TC,ONI,SOI,PDOI and NPGOI all have an influence on the late CM-TC.(3)The results of predictive value evaluation showed that the VAR(4-6)model could accurately predict the catches of sardines in the Northwest Pacific Ocean according to ONI,PDOI,NPGOI and AOI,and VAR4 could be used as the optimal model for sardines.It is suggested that acrossing to improved research methods and Integrating other fields in the future to further analyze the response mechanism of the fluctuation of fisheries resources to climate change.(1)A biomass dynamic model was constructed by adding parameters such as population dynamic process,fishing mode coefficient and natural mortality rate on the basis of a variety of climate-ocean indexes to reveal the influence process of climate-ocean change on fishery resource quantity;(2)The effects of large-scale marine currents and mesoscale vortex on small pelagic fish were studied based on physical ocean models and spatially coupled hydrodynamics models,combining with other major north Pacific climates such as North Pacific Oscillation(NPO),North Pacific Gyre Oscillation(NPGO),Arctic Oscillation(AO).