Application of Risk Analysis to a Stock Assessment of Swordfish (Xiphias gladius) in the North Pacific Ocean

Predicting future management actions and their uncertainty are important objectives in fisheries management. We used a Bayesian state-space production model incorporating parameter estimation uncertainty and process error to characterize current and future stock status for two stocks of swordfish (Xiphias gladius) in the Western and Central Pacific Ocean (WCNPO) and Eastern Pacific Ocean (EPO). The models were fit to commercial longline standardized catch-rate data from Japan, Taiwan, and USA. A risk analysis consisted of projections under alternative catch scenarios. Current (2012) exploitable biomass status for both stocks is highly likely to be >B_MSY. Current harvest rate in the WCNPO is likely <H_MSY, but there is a >50% chance that the EPO harvest rate is >H_MSY. The risk analysis showed that WCNPO catch can be ~16,000 metric tons (150% of recent catch) before reaching either a 50% probability of overfishing (H>H_MSY) or becoming overfished (B<0.5*B_MSY) by 2017. In contrast, an EPO catch of ~7,800 metric tons (80% of recent catch) will result in a 50% probability of overfishing. Overall, our findings suggest the stock of swordfish in the WCNPO is healthy given the current fishery but overfishing will likely occur in the EPO if recent catch levels persist.