The Feeding And Migration Of Todarodes Pacificus Based On The Stable Isotopic Values Of The Gladius

Todarodes pacificus was mainly distributed in the sea areas around the Japanese archipelago,the Yellow Sea and the East China Sea.T.pacificus was important cephalopod economic resource.The gladius is a hard tissue composed of chitin and protein in the body of cephalopods,and the gladius recorded the full information of life history of cephalopods.Theδ¹³C and ¹⁵N values of the gladius can be used to investigate the feeding ecology and migration path of T.pacificus.The study analyzed the growth characteristics of the gladius,and found that the gladius is significantly correlated with mental length and body weight of samples.The study proved that the gladius is a good carrier for studying biological characteristics of T.pacificus.On the basis of understanding biological characteristics of the gladius,the study analyzed the feeding ecology and migration path of T.pacificus in different years（2018,2019）and different sea areas（the East China Sea,the Sea of Japan）.The study further analyze the biological characteristics of T.pacificus and provide scientific basis for scientific management and development of T.pacificus resources.The main research results are shown below:（1）The growth characteristics of the gladius of T.pacificus.The samples of T.pacificus were caught in the East China Sea in the summer of 2019（June-August）.Principal component analysis showed that,gladius length（GL）,cones length（CL）and the length of greatest width of proostracum（GWPL）were fit to characterize the length of the gladius as the morphological parameters,while greatest width of vane（GWV）and greatest width of proostracum（GWP）were fit to characterize the width of the inner gladius as the morphological parameters.Results of the analysis of covariance（ANCOVA）showed that,there was no significant difference between sexes in the growth relationship between all characteristic parameters and mantel length（ML）,and there was also no significant difference between sexes in the growth relationship between all characteristic parameters and body weight（BM）.According to equation fitting and Akaike Information Criterion（AIC）analysis,the relationship between GWP and ML was best fitted with exponential functions,and the relationship between GL,GWPL and ML was best fitted with linear functions,and CL,GWV and ML was best fitted with logarithmic functions.The relationship between GWPL and BW was best fitted by linear function,and the relationship between GL,CL,GWV,GWP and BW were best fitted by logarithmic function.（2）The migration and feeding of squid T.pacificus in the Sea of Japan.For T.pacificus samples were caught in the Sea of Japan in 2018,when the proostracum of gladius grows to 120mm from the distal end,they all began to migrate to high-latitude and offshore sea areas,and the feeding behavior may have changed during the migration.And the feeding ability of the female group was stronger than the male group.（3）The migration and feeding of squid T.pacificus in the East China Sea.For T.pacificus samples were caught in the East China Sea in 2018 and 2019,when the proostracum of gladius grows to 120mm from the distal end,they all began to migrate to the low-latitude and inshore sea areas.In 2019,the T.pacificus’migration range was larger,which may be caused by the occurrence of El Ni?o event.With the growth of T.pacificus individuals and the migration process,the trophic level of the T.pacificus gradually increased in 2018,and the overall trophic level of the T.pacificus did not change much in 2019.（4）The migration and feeding of squid T.pacificus in the East China Sea and the Sea of Japan.For T.pacificus samples were caught in the East China Sea and the Sea of Japan,when the proostracum of gladius grows to 120mm from the distal end,they all began to migrate.For T.pacificus samples in the East China Sea,they migrated to the low-latitude and inshore sea areas,and the trophic level had no great changes during the migration process.For T.pacificus samples in the Sea of Japan,they migrated to the high-latitude and offshore sea areas,and the trophic level decreased gradually during the migration process.There are great differences in migration path and feeding ecology for T.pacificus in the East China Sea and the Sea of Japan.The difference of migration path in the two sea areas may be related to the different populations of T.pacificus caught,and the difference of feeding ecology may be related to the migration path.