The Use of Per Recruit Models for Stock Assessment and Management of Greasy Grouper Epinephelus tauvina in The Arabian Gulf Waters off Qatar

摘要

Per recruit models were applied to assess greasy grouper, Epinephelus tauvina, stock in the gulf waters off Qatar. Yield per recruit (Y/R) increased rapidly at low values of fishing mortality (F). At present natural mortality (M = 0.17 per year) and age at first capture (Tc = 7.6 years), the Y/R increased with increasing F to reach a maximum value of 1067.8 g per recruit at F = 0.65 per year. Above this level of F, Y/R was constant or slightly decreased. The current level of F is higher than the biological reference points F0.1 (0.15 per year), FSB40% (0.13 per year), FSB50% (0.08 per year) and FSB25% (0.24 per year). Increasing the Tc by one year resulted in a slight increase in the Y/R, while additional increases in Tc led to a decrease in Y/R values. At constant M, the increase in Tc caused an increase in F required to obtain the maximum Y/R until reaching a non-maximum state at the oldest Tc. At the current level of F, increasing the Tc by one year would result in a small increase in biomass per recruit (B/R), while further increases would lead to a decrease in B/R. At higher levels of F, any increase in Tc would cause a gradual increase in B/R, followed by a decline after a certain value of Tc. These results provide evidence of recruitment over-fishing at all optimum fishing levels, F0.1, FSB40%, FSB50% and at the threshold level, FSB25%. Therefore, sustainable management and conservation of greasy grouper in Qatari waters would require a decrease in F to levels less than F0.1 and FSB40%, which can be achieved through a reduction in fishing effort but not through an increase in Tc.