Future Stock Projections of Oceanic Whitetip Sharks in the Western and Central Pacific Ocean (Update on Project 101) DRAFT
The updated stock assessment for oceanic whitetip shark presented to the 15th WCPFC Science Committee (Tremblay-Boyer et al., 2019) showed that the stock was overfished and undergoing overfishing, but also highlighted a small reduction in stock depletion, with increases in recruitment and a reduction in fishing mortality relative to reference points under certain catch scenarios. However, since oceanic whitetip sharks are late-maturing and fishing mortality on juveniles is high, uncertainty remains as to the level of effectiveness of the non-retention measure active for the last 4 years of the assessment and the impacts of CMMs (CMM-2011-04 non-retention of the species, and CMM 2014-05 a ban on wiretrace or shark lines) on the timeline for recovery. The stock assessment characterized the uncertainty in the data and model parameters via a structural uncertainty grid where multiple (648) combinations of data and parameter values were used to show the range of plausible uncertainty to the inputs. This study updates the projections of Rice et al. (2021) with contemporary estimates of mortality at longline retrieval, post-release mortality, catch reductions and prohibitions of wire branchlines and shark lines. The study used the same representative subset of the structural uncertainty (108 runs) as in Rice et al. (2021) for projections. Future projections for the 2019 WCPO oceanic whitetip stock assessment are presented for five scenarios to assess the impacts of various potential management measures. Population projections illustrate a summary of spawning biomass in the latest time period (2031) relative to the equilibrium unfished spawning biomass (SB2031/SBF=0).