Age, growth, mortality, and yield-per-recruit for nagroor, Pomadasys kakaan, in Kuwait’s waters

Abstract

The age, growth and mortality of nagroor, Pomadasys kakaan, were determined from sectioned otoliths of fish from Kuwait waters. Estimated parameters of the von Bertalanffy growth function for pooled data were L ∞=62.16 cm, K=0.27 per year, and t 0=−0.47 year ( n=1183). Significant differences in length-at-age and estimated growth parameters were found between sexes, with females growing larger than males. Maximum age recorded was 36 years and the largest fish was 75 cm total length (TL). Natural mortality rate ( M) was 0.20 per year and total mortality rate ( Z) ranged from 0.24 to 0.36 per year. The effect of different fishing mortality ( F, 0.1–1.5), and M (0.20, 0.25, and 0.30), and age at first capture ( t c, 1.0–5.5) on yield-per-recruit of nagroor were evaluated. Higher yield-per-recruit occurred at lower M (0.20) and higher F (>0.80) at t c=3.5–4.0 years; however, at the current t c=5.1, marginal increase in yield beyond F=0.50 was small. The current F values were always below F 0.1 and maximum F max for all M values used in simulations. Because of uncertainties associated with the estimates of mortality, the option of increasing fishing effort to obtain higher yields could be considered, but reduction of mesh size to meet minimum marketable size ( t c=3.5 per year) would be preferable under the prevailing conditions in Kuwait’s fishery.