Estimation of Growth and Mortality Parameters of Cr oaker Atrobucca alcocki in Pakistani Waters

Abstract

Five demersal trawl surveys were conducted in the P akistani waters in October, November 2009 and August, October, November 2010. A total of 819 length-weight and 7,240 length-frequency data of Atrobucca alcocki were collected, the length ranged from 10 cm to 45 cm with the dominant length group from 19 to 29 cm. The total weight ranged from 14 to 928 g. The length-weight relationship ca n be expressed as W = 0.012* L 2.925 (R 2 = 0.972). Using the ELEFAN program in FiSAT computer package, the calculated von Bertalanffy growth function parameters were L ∞ = 47.25cm, K = 0.180 yr -1 . Total mortality ( Z ) was computed using the length-converted catch cur ve analysis at Z = 1.07 yr -1 . Natural mortality was computed as M = 0.494 yr -1 at an annual average sea surface temperature of 26°C, hence, the fishing mortality was computed as F =Z-M= 0.576 yr -1 . The Exploitation ratios (E) were computed as E max = 0.421, E 10 =0.355, E 50 =0.278. Yield per recruit analysis revealed that when t c was assumed to be 2, F max was calculated at 0.75 and F 0.1 at 0.6. When t c was assumed to be 1, F max was calculated at 0.55 and F 1.0 at 0.45. Current age at first capture was about 1 year and F current was 0.576, therefore, F current was larger than F 0.1 and F max . When biological reference point was F opt equal to M (0.494), current fishing mortality rate of 0.576 was larger than the target biological reference point. Keywords : Biological reference points, Bertalanffy growth fun ction, Length-converted catch curve, Natural mortality.