Estimation of natural mortality of Kuwait's grooved tiger prawn Penaeus semisulcatus (de Haan) using tag-recapture and commercial fisheries data

Abstract A new simple optimization procedure was used to estimate the natural mortality ( M ) of the heavily exploited Kuwaiti Penaeus semisulcatus (de Haan) stock using tagging data. The new M estimator was based on two tagging experiments with similar (constant) SB values (i.e. the product of initial survival after tagging and the reporting rate), but with different total mortality ( Z ) values. Two conventional methods were employed to evaluate M for direct estimation and comparison; one, modified Gulland's formulae, using 1982–1983 tagging-experiment data, and the other, catch per unit effort (CPUE) ratio, using 1986/1987–1990 industrial fishery CPUE data. The M estimate for males was 0.1314 per 20 days (2.4 per year) with a standard error of 0.0135. The female tagging experiments violated the critical assumption underlying the new M estimator; nevertheless, by comparing results from other methods, the male M value was accepted for females. The new M estimator and modified Gulland's formulae will likely produce reasonable estimates of M if compatible tagging experiments and fairly accurate Z values are used.