WCPFC MANAGEMENT OBJECTIVES WORKSHOP Manila, Republic of the Philippines 28-29 November 2012 APPLICABILITY OF HISTORICALLY BASED LIMIT REFERENCE POINTS TO THE NORTHERN TUNA STOCKS IN THE PACIFIC

The northern tuna stocks in the Pacific have specific characteristics: long-term large variability of the total biomass, sparse stock-recruitment relationship, and no obvious indication of recruitment overfishing even though the spawning stock biomass sometime fell into in a very low level. In contrast, southern stocks in the Pacific have one way decreasing trends in shorter exploitation histories. In consideration of these characteristics, we investigated the applicability of historically based limit reference points (LRPs) to the northern tuna stocks. We compared the performance of Floss, which is a typical historically based LRP, with Fmsy, which is a MSY based LRP, for datasets that simulated the northern and southern stocks. As a result, the numerical simulations indicated that when the stock-recruitment relationships is sparse (steepness is over 0.6), MSY based LRP and historically based RP are applicable for northern and southern stocks because of no risk or little risk to be recruitment overfishing. However, if process errors given in the simulation are large, the MSY based LRP has a large risk to exceed the recruitment overfishing for the northern stock than historically based one, even if the steepness is large. Generally, a historically based LRP is an easily understandable concept as a LRP for avoiding recruitment overfishing. Additionally, it uses relative historical trends instead of absolute value which usually includes large uncertainty. Moreover, historically based LRPs have been commonly applied to the stock management. Therefore, it is valuable to consider the historically based LRP as an option for the northern stocks in the hierarchical approach proposed by the WCPFC, especially when applied to the northern tuna stocks.