Updated Stock Assessment Of Blue Marlin (Makaira Nigricans) In The Indian Ocean Using JABBA

Three Bayesian State-Space Surplus Production Model scenarios were run to assess blue marlin (Makaira nigricans) in the Indian Ocean using the JABBA framework, based on catch and effort data up to and including 2020. A ‘drop one’ sensitivity analysis indicated that omitting any of the CPUE time-series would not significantly alter the stock status. Similarly, a retrospective analysis produced highly consistent results for stock status estimates back to 2015 and therefore provided no evidence for an undesirable retrospective pattern. The B/B_MSY trajectory declined from the mid-1980s to 2007. A short-term increase in B/B_MSY occurred from 2007 to 2012, which is thought to be linked to the NW Indian Ocean Piracy period. Thereafter, the B/B_MSY trajectory again declines to the current estimate. F/F_MSY increased since the mid-1980s and despite a recent decline, F/F_MSY remains above 1. Terminal points of the time series fall within the red quadrant of the Kobe plot in all scenarios (61.4% - 74% probability). As such, the blue marlin stock in the Indian Ocean is currently “overfished” and “subject to overfishing”. However, the current catches of blue marlin are marginally lower than the estimated MSY for all scenarios.