Growth and mortality of small yellow croaker (Larimichthys polyactis) inhabiting Haizhou bay of China

Length frequency data of small yellow croaker (Larimichthys polyactis) were acquired from the survey vessel in May, July, September and December, 2011 in Haizhou Bay of China. In this study, 921 fish individuals were analyzed for the estimation of growth and mortality parameters. Between length and weight, the power coefficient b was 2.7321, 2.9703, 3.0418 and 2.7252 for the 4 surveying months, respectively. The estimated von Bertalanffy growth function parameters were 230mm (L (a)) and 0.26yr(-1) (K) as were calculated with ELEFAN method equipped in FiSAT computer package. With length-converted catch curve analysis, the total mortality rate (Z) and its 95% confidence interval were 2.16 (1.69-2.64) yr(-1), 0.59 (0.15-1.04) yr(-1), 1.16 (0.80-1.52) yr(-1) and 0.96 (0.70-1.23) yr(-1) for the 4 surveying months, respectively, with the pooled data the value was 1.15 (0.81-1.48) yr(-1). The natural mortality rate (M) was 0.516 yr(-1) as was calculated with Pauly's equation (the annual average sea water temperature was 11A degrees C). Therefore, fish mortality rate was 0.634 yr(-1). The yield-per-recruit analysis indicated that when t (c) was 1, F (max) was 0.7 and F (0.1) was 0.55. Currently, the age at first capture is about 1 year and F (current) was 0.634. Therefore, F (current) was larger than F (0.1) and less than F (max). This indicates that current fish mortality is at a dangerously high level. With Gulland method, the biological reference point for fishery (F (opt)) was estimated as 0.516 yr(-1), lower than current fish mortality. Accordingly, reducing catch in the region was strongly recommended.