Length-frequency, Yield and Biomass Per Recruit Analysis for Yellowfin Tuna, Thunnus albacares (Bonnaterre 1788) in the Arabian Sea off Oman

The present study was carried out to evaluate the stock of Thunnus albacares (Bonnaterre 1788) in the Arabian Sea off Oman. A random sample of 3,690 fish representing a wide range of total lengths (44-156 cm) and weights (3-64 kg) were collected from Al-Sharqya area, Oman from January to December 2007. Length-frequency analysis and yield and biomass per recruit models were used.Values of the von Bertalanffy growth parameters fit to size-at-age data were: asymptotic length (L∞)=188.2 cm, curvature parameter (K)= 0. 33 year^-1, and hypothetic age at zero length (t0) = −0.66 year. Using the length-converted catch curve, total mortality (Z) was estimated as 1.72 year^-1. Natural mortality coefficient M was 0.53 year^-1and fishing mortality coefficient F was 1.19 year^-1 ,. The mean length at first capture (Lc) estimated from the analysis of probability of capture of each length class was 69.67 cm. The yield per recruit (Y/R) was 8,983 g per recruit(g/r), which is less than the maximum value (9,683 g/r) that could be obtained at a fishing mortality of 0.6 year^-1. The biomass per recruit (B/R) represented about 10 % of the virgin biomass, indicating a state of overexploitation. To increase the Y/R and B/R of T. albacares the results suggest increasing the length at first capture through increasing the mesh size of artisanal gillnets.