Research On Trophic Niche And Geographical Populations Of Larimichthys Crocea And Larimichthys Polyactis In The Yellow Sea And The East China Sea Based On Fish Scale Stable Isotopes

Large yellow croaker(Larimichthys crocea)and small yellow croaker(Larimichthys polyactis)are important marine economic fish species in China,which have suffered serious resource decline in recent decades.Studying the trophic niche and geographical populations of these two fish species will help to restore their fishery resources.Fish scales are skin appendages of fish,which are metabolic inertness and can store the complete life history information.In this study,the author first analyzed the correlation of carbon(δ13C)and nitrogen(δ15N)stable isotopes between fish scales and white muscle tissue of fishes from the Yellow Sea and the East China Sea.Then,δ13C and δ15N of fish scales were used to analyze the feeding characteristics,trophic levels and trophic niche of large yellow croaker and small yellow croaker in the Yellow Sea and the East China Sea.The differentiation results of geographical populations of them were discussed taking the stable isotopes of carbon,nitrogen and oxygen(δ18O)in fish scales and Fulton’s condition factor(K value)as variables by means of discriminant analysis and cluster analysis.In this dissertation,the application value of fish scale stable isotopes in trophic information and population differentiation of marine fish is verified,which provides an important supplement to the research conclusions on trophic information and geographical populations of large yellow croaker and small yellow croaker in the Yellow Sea and the East China Sea.The main results are as follows.First,by analyzing 16 fish species from the Yellow Sea and the northern East China Sea,it is confirmed that the stable isotopes of carbon and nitrogen in fish scales and white muscle tissue are highly correlated(δ13C,r=0.807,P<0.001;δ15N,r=0.830,P<0.001).Feeding characteristics were determined by benthos proportion(Bp value),and it was confirmed that fish scale δ13C could represent the feeding characteristics of marine fishes.The δ15N of fish scales can be used to characterize the trophic levels of marine fishes after calculation.Second,for large yellow croaker in the Yellow Sea and the East China Sea,there is no spatial difference in feeding characteristics,but there has been a great change in feeding characteristics in recent decades,from mixed feeding to complete benthosfeeding.The trophic levels increased gradually from north to south,ranging from 2.88 to 3.67,with an average of 3.21,showing a downward trend compared with historical data.Third,the Bp value of small yellow croaker in the Yellow Sea was between 0.72 and 0.79,which was mixed feeding and did not change much in recent decades,while the Bp value of that in the East China Sea was above 1,which changed from mixed feeding to complete benthos-feeding in recent decades.The trophic levels of small yellow croaker in the Yellow Sea and the East China Sea decreased first and then increased from north to south,ranging from 3.01 to 3.86 with an average of 3.49,and the changes were relatively stable in recent decades.Fourth,the result of trophic niche showed that,in the southern Yellow Sea and the central and northern East China Sea,the trophic niche width and core trophic niche width of large yellow croaker were 3.58 and 1.05,respectively,and those of small yellow croaker were 10.14 and 3.96,respectively.The overlap of trophic niche between them accounted for 63.4%of large yellow croaker and 22.2%of small yellow croaker.Small yellow croaker occupied a larger trophic niche and core trophic niche than large yellow croaker,and there was significant trophic niche overlap for large yellow croaker.Fifth,combination of δ13C,δ15N,δ18O of fish scale and K value had a discriminant success rate of 40.0%～65.7%for large yellow croaker among regions,and the combination with the highest discriminant success rate was δ13C+δ15N+δ18O.The discriminant success rate of small yellow croaker was 47.8%～69.6%,and the combination with the highest discriminant success was δ13C+δ15N+δ18O+K.The analysis result of geographical populations showed that large yellow croaker could be divided into southern Yellow Sea-northern East China Sea populations,and central East China Sea-Taiwan Strait populations.Small yellow croaker can be divided into northern Yellow Sea populations,central and southern Yellow Sea populations,and East China Sea populations.Sixth,some suggestions for conservation of large yellow croaker and small yellow croaker in the Yellow Sea and the East China Sea were put forward.For large yellow croaker,the fishing length should be strictly controlled and a reasonable ecological corridor should be set up.For small yellow croaker,it is recommended that the existing conservation policy be continued and the fishing effort in the East China Sea reduced.