Estimation of Atlantic bonito (Sarda sarda) stock status in the Senegalese Exclusive Economic Zone (SEEZ) from the catch-based model (CMSY) and length-based bayesian estimation (LBB) method

Abstract

Among the seven major small tuna species defined in the ICCAT priority list for future studies, Atlantic bonito (Sarda sarda) is the most heavily targeted by artisanal and industrial fisheries in many coastal areas. Considering this high pressure and the limits of previous studies on its status in some areas of the Atlantic Ocean, this study focused on assessing the Atlantic bonito stock mainly harvested by the artisanal fisheries in the Senegalese Exclusive Economic Zone (SEEZ) using two data-limited approaches (LBB and CMSY). These models used the recorded length composition, catch, and CPUE data for Atlantic bonito caught by various fishing gears to provide significant fisheries reference points to evaluate the stock status of this species. The LBB model indicated an Atlantic bonito healthy stock status with B/BMSY values ranging from 1.3 to 1.6 and B/B0 values varying from 0.47 to 0.61 of the main scenarios performed (BON_AFG_CL, BON_GN_Length, and BON_PS_Length). The results estimated by LBB are consistent with those obtained by CMSY. The CMSY model results demonstrate that the SEEZ Atlantic bonito stock is in a sound condition in the final year of the main scenarios analyzed (BON, BON-bt, BON-GN-bt, and BON-PS-bt) with sustainable relative stock biomass (B2018/BMSY= 1.13 to 1.3) and fishing pressure levels (F2018/FMSY= 0.52 to 1.43). However, the results of the two models show that longlines and sleeping nets negatively affect this species’ stock in this area, showing a slightly overfished and overfished stock status, respectively. The results of the scenarios formulated by these two fishing gears (BON_LL_Length, BON_SN_Length for LBB and BON-LL-bt, BON-SN-bt for CMSY) are below the reference values. LBB shows Lc/Lc_opt values ranging from 0.61 to 1, B/BMSY from 0.49 to 1, and B/B0 from 0.18 to 0.39. For CMSY, these two scenarios show a B/BMSY varying between 0.33 and 0.8.