Population dynamics of Japanese threadfin bream Nemipterus japonicus from Pakistani waters

Abstract

Japanese threadfin bream Nemipterus japonicus (Bloch, 1791) is among the most abundant and commercially important species in Pakistan. From the coast of Pakistan, four demersal trawl surveys in October–November 2009 and May–June, August, October and November in 2010 were carried out. The purpose of this study is to estimate the population dynamics and status of the stock of the N. japonicus from Pakistani waters based on the research trawl surveys from the research area. The data consist of n=784 length-weight pairs and n=7 530 length frequency with the maximum length and weight of 29 cm and 358 g respectively. The length frequency data were analyzed using ELEFAN method in FiSAT computer package. The parameters of length and weight relationship were b=2.778, a=0.032 and R 2=0.973. The estimated von Bertalanffy growth function parameters were L ∞=30.45 cm, K=0.270 year−1. Based on length-converted catch curve analysis the total mortality (Z) during this study was estimated at 0.960 year−1. The natural mortality coefficient (M) was 0.74 year−1 using Pauly’s equation (the annual average sea surface temperature was 27°C), therefore, the fishing mortality coefficients (F) were 0.22 year−1. The yield per recruit analysis indicated that when t c was 2, F max was estimated at 1.2 and F 0.1 at 1.1. When t c was 1, F max was estimated at 0.95 and F 0.1 at 0.8. Because current age at first capture is about 1 year and F current was 0.22, F current is smaller than F 0.1 and F max, which indicated that the fishery is about in a safe condition. When using Gulland (1971) biological reference point, F opt was equals to M (0.74). The current fishing mortality rate of 0.22 was smaller than the target biological reference point.