Stock assessment of Yellowfin tuna, Thunnus albacares (Bonnaterre, 1788) using the LBB and LB-SPR methods in the northern Oman Sea, Iran

The current work aimed to develop a framework for the estimation of the optimized catch limit of the Yellowfintuna(YFT),Thunnus albacaresstock using catch data in the Iranian southern waters.In this study, two methods were employed to determine the biological reference points (BRPs) of this species. Biometry data was collected for 18 years (1993-2019) and the optimized catch limit was estimated using the limited data approaches. In an estimation method of Length-based Bayesian biomass(LBB), the highest length of this species was calculated as 166 (163-169) cm. The estimate of F/M= 1.9 (1.35-2.5) confirms the overfishing of yellowfin tuna, but the estimate of B/B0=0.17 (0.109-0.238) shows the overfishing of the biomass. In an estimation method of length-based spawning potential ratio (LB-SPR), F/M>2.5 is upper the level that probably results in the maximum sustainable yield (F/M= 0.8-1.0). In the present study, the spawning potential level of the population was estimated at approximately 11%, which means over-exploitation of this species so far. The results showed that the exploitation ratio of YFTstock is overfishing (overexploitation) and a decrease in exploitation ratio and fishing effort are proposed. Regarding the condition of yellowfin tuna stock, both LBB and LBSPR methods confirmed each other and there is no big difference between them.