Study on the correlation between spatial distributions of the spawning groups and the power b in length-weight relation function of small yellow croaker(Larimichthys polyactis)

Studies on fish spawning group are always the focus of fisheries science. Spawning periods and areas are important parts of fish ecological habit studying. Power b in exponent relationship between fish body length and weight as spawning period indicator has been tested and proved with one whole year data in previous paper. Based on the above,this study tries to analysis the spatial character of fish spawning groups by power b at a time point with the data collected from a bottom trawl survey in the 4 seasons of 2004 in the East China Sea. The results show that,ripening small yellow croakers appeared only in spring,however immature individuals appeared in all of 4 seasons,which suggests the presence of "skip spawning" phenomenon. Another finding is that different spawning mature stages can not be distinguished only based on the value of power b,neither the difference between the spawning and non-spawning; while the average power b of sites including spawning individuals appeared lower than that in a constant speed growing,and similar characteristics also occurred in the space,where the relatively low power b generally occurred in the waters with relative high concentration of spawning individuals. Based on power b,three areas with relative high concentration of ripening individuals were inferred,including the offshore of Zhoushan fishing ground,the southwest side of Jeju Island and the adjacent water between Jiangwai and Zhouwai fishing grounds.