Chub Mackerel (Scomber Japonicus ) In The East China Sea And Yellow Sea

In recent years,there had been a gradual increase in the proportion of fishery products of Chub mackerel in the East China Sea and Yellow Sea. It had higher status in fisheries production. The resources of Chub mackerel still had a certain potential of exploiting relative to the other overexploiting resources. The study for the population structure and reproductive biology of Chub mackerel was helpful for grasping its life cycle,estimateing its population and resource,enriching the ways and means of management of fisheries resources,assisting the rational exploitation and protection of this resource.In this paper,firstly combining the studies at home and aboard,the old and new analysis methods of population structure of fish were summarized and generalized initially, and the merit and demerit. The study is aimed at provide the approach of stock identification and partition of fish resources in the sea region of China.Based on the samples from peak of major spawning collected in the Southern and Eastern Fujian fishing ground, Wenzhou-Taizhou and Yantai-Weihai fishing grounds during January to May 2010, the paper analyzed the morphological differences of mature stock of Chub mackerel (Scomber japonicus). Twenty characters of each individual were measured through the truss method, and the data was standardized by the allometric method was used to remove the influences of size differences on analysis. Furthermore, multivariable analysis of variance method was used to examine the differences between the female and male individuals from four sampling areas. The results indicated that as for character 2-4, significant difference between the females and males of Wenzhou-Taizhou fishing grounds was found (P < 0.05), but not for other characters or individuals from other fishing grounds. Therefore, we did not separate the males and females for further analysis in this study. The discriminant formula was built by Principal component analysis (PCA) and Stepwise discriminant function analysis (DFA). Three principal components were constructed, and the cumulative contributory ratio was 86.63 %. Principal component 2 was affected by the length of second dorsal fin and anal fin, while the extremity of operculum and starting point of pelvic fin affected principal component 3 especially. The principal component analysis showed that the body length had brought out the morphological difference of mature stock in four sampling areas. The discriminant function of four mature stocks was established by DFA, which showed the range of discriminant accuracy was 97.06%～100% for P1, 97.14%～100% for P2, and general discrimination rate was 99.2%. In summary, present research suggested that the morphological differences of mature stock of Chub mackerel were significant in the four sampling areas in the East China Sea and Yellow Sea was drawn out.Based on the variations of 16SrRNA gene and D-loop sequences in mitochondria of four spawning group of chub mackerel in the East China Sea and the Yellow Sea, this study discusses its population division problems preliminarily. The preliminary study base on the two genes and morphology characters as follows: the samples of Yantai-Weihai fishing ground, the samples of Wenzhou-Taizhou fishing ground and the samples of Eastern Fujian fishing ground, the samples of Southern Fujian fishing ground can be divided into three branches.The former two branches of the genetic relationship between than with the Taiwanese fishing grounds branch closer.Finally, this paper analyzed the population structure of chub mackerel of different spawning groups in the East China Sea and Yellow Sea preliminarily, associated with the sample composition, the relationship between fork length and weight, sex ratio, sexual maturity coefficient and fecundity etc. The results showed that the sex ratios were according with the proportion of 1:1 for the samples from all fishing grounds expect Wenzhou-Taizhou (χ2=4.129, P<0.05). Higher sexual maturity rate for females were found compared with male individuals (P<0.05). Generally the absolute individual fecundity of chub mackerel in the East China Sea was lower than that in the Yellow Sea, and the egg diameter increased with the latitude changing from south to north.