Population dynamics parameters of narrow-barred Spanish mackerel, Scomberomorus commerson (Lacèpéde, 1800), from commercial catch in the northern Persian Gulf

Population dynamics parameters of Scomberomorus commerson in Bushehr area waters of Iran were analyzed between October 2011 and September 2012. Fork length frequencies were collected from the gill net commercial catch. Von Bertalanffy growth function was used to estimate growth parameters K and L∞. Instantaneous total mortality rate (Z), instantaneous natural mortality rate (M) and the instantaneous fishing mortality rate (F) were also calculated. Resource status was evaluated by comparing estimates of the fishing mortality rate with target (Fopt) and limit (Flimit) biological reference points. FiSAT program was used to assess growth and mortality parameters. Based on the growth curve analysis, growth parameters were: K=0.5year−1 and L∞=148cm. Instantaneous total mortality was Z=0.97year−1. The estimate of M=0.56year−1 and F=0.41year−1, resulting in an exploitation rate (F/Z) of E=0.42year−1. Target and limit biological reference points were: Fopt=0.28year−1 and Flimit=0.37year−1. Size at capture at probabilities of 0.25 (L25), 0.5 (L0.5) and 0.75 (L0.75), were 46.3 cm, 55 cm and 60.2 cm respectively. Longevity (Tmax) was calculated as 3/K equal to 6 years. The exploitation rate (E) did not indicate overfishing; however, Fopt and Flimit rates were lower than fishing mortality (F), suggesting that overexploitation occurred. Growth parameters in the present study showed that the gillnet fishery catches of S. commerson that are of ages 1 or 2, which may not have reached maturity. Gillnet mesh size can be a factor why the catch is composed of mostly small, immature fish. Therefore, changes in mesh size and net size should be considered.