Estimation of Growth and Mortality Parameters of Croaker Atrobucca alcocki in Pakistani Waters

Five demersal trawl surveys were conducted in the Pakistani waters in October, November ۲۰۰۹ and August, October, November ۲۰۱۰. A total of ۸۱۹ length-weight and ۷,۲۴۰ length-frequency data of Atrobucca alcocki were collected, the length ranged from ۱۰ cm to ۴۵ cm with the dominant length group from ۱۹ to ۲۹ cm. The total weight ranged from ۱۴ to ۹۲۸ g. The length-weight relationship can be expressed as W= ۰.۰۱۲*L۲.۹۲۵ (R۲= ۰.۹۷۲). Using the ELEFAN program in FiSAT computer package, the calculated von Bertalanffy growth function parameters were = ۴۷.۲۵cm, K= ۰.۱۸۰ yr-۱. Total mortality (Z) was computed using the length-converted catch curve analysis at Z= ۱.۰۷ yr-۱. Natural mortality was computed as M= ۰.۴۹۴ yr-۱ at an annual average sea surface temperature of ۲۶°C, hence, the fishing mortality was computed as F=Z-M= ۰.۵۷۶ yr-۱. The Exploitation ratios (E) were computed as Emax = ۰.۴۲۱, E۱۰ =۰.۳۵۵, E۵۰ =۰.۲۷۸. Yield per recruit analysis revealed that when tc was assumed to be ۲, Fmax was calculated at ۰.۷۵ and F۰.۱ at ۰.۶. When tc was assumed to be ۱, Fmax was calculated at ۰.۵۵ and F۱.۰ at ۰.۴۵. Current age at first capture was about ۱ year and Fcurrent was ۰.۵۷۶, therefore, Fcurrent was larger than F۰.۱ and Fmax. When biological reference point was Fopt equal to M (۰.۴۹۴), current fishing mortality rate of ۰.۵۷۶ was larger than the target biological reference point.

Keywords:

Biological reference points , Bertalanffy growth function , Length-converted catch curve , Natural mortality