Study On Habitat Evaluation Of Cololabis Saira In The Northwest Pacific Based On Biogeochemical Technology

Pacific saury（Cololabis saira）belongs to Beloniformes,Scomberesocidae,Cololabis,also known as saury.It is a cold-water pelagic migratory fish that gathers at the intersection of cold and warm ocean currents.It is distributed in the waters of19°～58°N in the subtropical and temperate zone of the Pacific Ocean along the coast of Asia and the Americas,and its suitable temperature range is 10～24℃.The life cycle is short,its growth is relatively rapid,and it is very sensitive to environmental changes.The habitat distribution are greatly affected by environmental factors.In order to ensure the rational development and scientific management of saury resource,scientific mastery of its habitat distribution and life history is the key.Otolith is important hard tissues of fish,which record the ecological information of the entire life stage of the fish.The metabolism of muscle tissue is relatively active,which can reflect the life history information of the organism a few weeks before death.For this,it is planned to analyze the otolith trace elements and muscle stable isotopes of saury,to understand and master the age and growth of saury,habitat distribution and environmental life history information,provide a basis for comprehensively grasping the biology of saury fishery resources.According to the saury samples collected by the saury fishing boat"Lu Peng Yuanyu 027"in the Northwest Pacific Ocean from July to November 2018,the microstructure growth pattern of otolith was analyzed and verified by the otolith wheel pattern,and the saury’s day ages were estimated.The distribution of day ages,hatching group division and growth of saury are studied;through stable isotopes of muscle,based on the generalized additive model（GAM）,δ¹³C,δ¹⁵N and body length,latitude,distance from shore and other biologic and abiotic factor were established the relationship respectively,to explore the habitat changes and migratory habits of saury;analyze the composition and content of trace elements in otolith,study the change trend of the ratio of trace elements to Ca in time series,and select out key elements to classify saury’s different life history stages,explore the relationship between key elements and marine environmental factors,infer the potential habitat location of saury in different life history stages and reconstruct the migration path of saury populations,so as to provide basic data for the evaluation and research of saury habitat.The main results are as follows:（1）Population composition and growth characteristics of saury.Studies have shown that among 166 saury samples,the age range is 277-560 d,the average age is（424±68）d,and the dominant age group is 360-450 d,accounting for 55%of the total,the smallest age is 277 d,the body length is 250 mm,and the body weight is 87g.The largest is 560 d,the body length is 301 mm,and the body weight is 141 g;the spawning date is from March 2017 to February 2018,according to the incubation season,the spawning groups are divided into spring group,summer group,autumn group and winter group.The peak of the spawning period occurs from June to August（summer）;there is a significant correlation between body length,body weight and day age（p<0.05）,and there is no significant correlation between males and females（P>0.05）;the relationship between body length,body weight and age are all suitable for Logistic growth model（AIC value is the smallest and r²is the largest）,and the relationships are as follows:（?）There is no significant difference in body length and weight between males and females（p>0.05）.The average absolute growth rate and relative growth rate of body length are 0.816 mm/d and 0.06097,respectively.The average absolute growth rate and relative growth rate of body weight are The growth rate was 0.925 g/d and0.15366.Both the absolute growth rate and the relative growth rate decreased with the increase of day age,then increased,and finally decreased.（2）Study on habitat Change of Cololabis saira based onδ¹³C andδ¹⁵N Stable isotopes.Studies have shown that the range ofδ¹³C is-23.58～-20.69‰,and the average value is-21.71±0.69‰;the range ofδ¹⁵N is 6.49～11.11‰,and the average value is 8.51±1.00‰,and theδ¹³C andδ¹⁵N of male and female are no significant difference（P>0.05）;the distributions ofδ¹³C andδ¹⁵N between different body length groups are relatively similar,showing a trend of rising first and then stable;the best predictor combination ofδ¹³C is BL+Lat+DSB+chla And these variables have a significant effect on theδ¹³C value of the saury muscle（P<0.05）.The deviation explanation rate of the model is 56.8%.The best predictor combination ofδ¹⁵N is Lat+DSB,and these variables also have a significant effect on theδ¹⁵N value of the saury muscle（P<0.05）.and the deviation interpretation rate of the model is 45.8%;through analysis,it is believed that the 1-year-old saury inhabits in the Oyashio waters,and then migrates south to the Kuroshio-Oyashio mixed waters;based on the results of the GAM model,it show thatδ¹³C is negatively correlated with latitude and positively correlated with body length.δ¹³C first decreases and then increases with the increase in distance from the shore,andδ¹³C first increases and then decreases with the increase of chlorophyll a.δ¹⁵N is negatively correlated with latitude,andδ¹⁵N decreases firstly,then slowly increases and then continues to decrease with the increase of nearshore distance.Based on the analysis betweenδ¹³C,δ¹⁵N and various explanatory variables,it is further verified that the 1-year-old Cololabis saury has experienced a southward migration and its habitat has changed.（3）Evaluation of saury habitat based on otolith trace elements.The results show that the main trace elements in saury otolith are natrium,calcium,strontium,magnesium,ferrum,copper and barium;based on the random forest method,Sr/Ca,Cu/Ca and Mg/Ca can be used as potential markers to construct the habitat history of saury;using regression tree model cluster analysis obtain 5 clusters and 4 critical points,the clustering results are defined as 5 life history stages;multiple linear regression analysis select strontium and magnesium used as indicators of sea surface temperature（SST）,and a multiple linear regression model is established to estimate that the SST ranges of the hatching ground,feeding ground,overwintering ground and spawning ground,they are 14.37-20.30℃,14.48-19.64℃,13.62-19.68℃and14.26-20.12℃respectively;based on Bayesian model,the potential habitat distribution area of Cololabis saury in different life history stages is inversely deduced.The embryonic stage,juvenile stage,sub-adult stage,adult stage and spawning stage the most possible respectively may distribute in 151°-153°E,35°-38°N,153°-156°E,38°-42°N,143°-147°E,35°-38°N,136°-144°E,30°-32°N and 150°-153°E,35°-37°N sea area,and reconstructed the potential migration path of the spring-summer cohort of Cololabis saury.