Feeding ecology of Japanese Spanish mackerel(Scomberomorus niphonius)along the eastern coastal waters of China

Feeding activities provide necessary nutrition and energy to support the reproduction and development of fish populations.The feeding ecology and dietary plasticity of fish are important factors determining their recruitment and population dynamics.As a top predator,Japanese Spanish mackerel(Scomberomorus niphonius)supports one of the most valuable fisheries in China.In this study,the feeding ecology and diet composition of Japanese Spanish mackerel spawning groups were analysed based on samples collected from six spawning grounds along the eastern coastal waters of China during spring(March to May)in 2016 and 2017.Both stomach contents and stable isotope analysis were conducted.Stomach content analysis showed that spawning groups of Japanese Spanish mackerel mainly fed on fish,consuming more than 40 different prey species.Diets were significantly different among sampling locations.The most important prey species were Stolephorus in Fuzhou,Japanese anchovy Engraulis japonicus in Xiangshan,Euphausia pacifica in Lüsi,sand lance Ammodytes personatus in Qingdao and Weihai,and Leptochela gracilis in Laizhou Bay.Stable isotope analysis showed that the trophic level of Japanese Spanish mackerel was relatively high and generally increased with latitude from south to north.In the 1980 s,the diet of Japanese Spanish mackerel was dominated solely by Japanese anchovies in the eastern coastal waters of China.The results in the present study showed that the importance of Japanese anchovies declined considerably,and this fish was not the most dominant diet in most of the investigated waters.Both the spatial variations in diet composition and changes in the dominant diet over the long term indicated the high adaptability of Japanese Spanish mackerel to the environment.Combining the results of stomach analysis and stable isotope analysis from different tissues provided more comprehensive and accurate dietary information on Japanese Spanish mackerel.The study provides essential information about the feeding ecology of Japanese Spanish mackerel and will benefit the management of its populations in the future.

Stock Structure Analysis of the Japanese Spanish Mackerel Scomberomorus niphonius(Cuvier, 1832) Along the China Coast Based on Truss Network

The Japanese Spanish mackerel Scomberomorus niphonius(Cuvier,1832)is widely distributed in the subtropical and temperate waters of the northwestern Pacific Ocean,supporting one of the most important commercial fisheries in China.However,ignoring the potential population structure changes induced by fishing pressure and climate change may undermine the population stability under the current management strategy.In this study,the population structure of the Japanese Spanish mackerel was investigated based on a morphometric truss network system.A total of 534 individuals were randomly collected from commercial gill nets spanning eight major spawning grounds in the Bohai,Yellow,and East China Seas during the peak spawning seasons respectively.A total of 17 measurements(including eye diameter)were conducted in each specimen and subjected to principal component analysis(PCA)and discriminant function analysis(DFA).The results of PCA indicated that the first two factors cumulatively caused 78.38%of the total morphometric variation and observable differences,primarily fin the caudal and trunk areas.The results of DFA revealed that the eight spawning groups can be divided into three stocks,i.e.,southern,middle,and northern stocks,with 68.7%of total accuracy.In contrast to previous studies,the spawning groups of the Japanese Spanish mackerel demonstrated a tendency to disperse to northern regions.In conclusion,this study found that to maintain the stability of the population structure and the total production of Japanese Spanish mackerel S.niphonius(Cuvier,1832),a newly revised management method should be developed and implemented.