Estimation of fisheries reference points for Longtail tuna (Thunnus tonggol) in the Iranian southern waters (Persian Gulf and Oman Sea)

In the present research, the Catch-only method was used to determine the biological reference points (BRPs) of Longtail tuna (LOT) in Iranian southern waters (Persian Gulf and Oman Sea). Depletion-based stock reduction analysis (DBSRA) and Catch maximum sustainable yield (CMSY) models were used to estimate BRPs by applying data from 1997 to 2018.The B/B_MSY was calculated as smaller than 1.0 in both models, while F/F_MSY was mostly higher than 1.0, which indicates the overfishing of Longtail tuna in this area. In 2012, the F/F_MSY ratio has exceeded over 1.01 and the B/B_MSY ratio with 2 years delay was declined in 2014. Consequently, the biomass reduction followed in 2016, declined to the below of B_MSY and the fishing pressure was not adjusted to combat. In comparison, DBSRA model indicated more cautious than CMSY in BRPs estimation for LOT in Iranian southern waters. Based on BRPs, it is recommended to implement an adjustment of annual harvest (around 55 thousand tons) as the simple (even quick) fisheries management strategies in order to guarantee the sustainable yield of this species in southern waters of Iran. We also recommend that catch-only methods could be treated as a temporary stepping-stone while sufficient data (e.g. size or age composition) is available for more reliable methods to be applied.