Assessment of Indian Ocean Striped Marlin (Tetrapturus audax) Stock Using JABBA

Six scenarios were run using the Bayesian State-Space Surplus Production Model JABBA to assess the Indian Ocean striped marlin (Tetrapturus audax). A ‘drop one’ sensitivity analysis indicated that omitting any of the “new” CPUE time-series would not significantly alter the stock status. Similarly, a retrospective analysis produced highly consistent results for stock status estimates back to 2009 and therefore provided no evidence for an undesirable retrospective pattern. The omission of historical CPUE time-series was considered on the advice of CPC scientists providing the CPUE standardization analyses, and so data from 1970 was only included in two scenarios: S1 and S3. The results for the six alternative scenarios estimated MSY between 4,430 and 4,826 tons, median estimates of B/B_MSY ranged between 0.26 - 0.32 and estimates of B/K were between 0.06 - 0.13. All scenarios produce B/B_MSY trajectories that steadily declined from the late 1970s to 2010 before leveling at the approximate current B/B_MSY estimates. There has been a steady increase of F/F_MSY since the 1970s, which has only recently showed signs of slowing. Individual Kobe biplots were similar among all scenarios and each indicated a >96% probability that the Indian Ocean striped marlin stock is overfished and subject to overfishing – which is a result comparable with the 2018 assessment for this species.