A new stock assessment was completed in 2020 by the Albacore Working Group (ALBWG) of the International Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC) (ISC/20/Annex/12, SAC-11-INF-I). The north Pacific albacore tuna stock has been exploited for a long time, the catches were the highest in 1976 (about 127,000 t) and the lowest in 1991 (about 37,000 t). During the assessment period (1994-2018), the highest catches were in 1999 (about 119,000 t) and the lowest in 2018 (about 52,000 t). About 2/3 of the catches come from surface fisheries (troll and pole-and-line) that harvest mainly juveniles, and the rest from longline fisheries. On average, about 20% of the catches are taken within the area of application of the Antigua Convention.

The assessment was done using the “best model” approach. The working group concluded that the stock was not experiencing overfishing and was probably not overfished as shown in (Figure F-2)

Figure F-2 Effort in vessel-days and number of vessels for the North Pacific albacore tuna in the eastern Pacific Ocean.

And also in (Table F-1).

The current depletion is 0.46 ((SSB(2018))/SSB_d , where SSB_d is the dynamic spawning stock biomass without fishing for 2018)). The ratio of ((SSB(2018))/(S(MSY)) = 3.01)). The relative current fishing mortality is (F(2015-2017))/(F(50%))= 1 , (F(2015-2017))/(F(20%)) =0.62, (F(2015-2017))/(F(MSY)) =0.60. The current depletion is 0.46 ((SSB(2018))/SSB_d , where SSB_d is the dynamic spawning stock biomass without fishing for 2018)). The ratio of ((SSB(2018))/(S(MSY)) = 3.01)). The relative current fishing mortality is (F(2015-2017))/(F(50%))= 1 , (F(2015-2017))/(F(20%)) =0.62, (F(2015-2017))/(F(MSY)) =0.60

The current IATTC conservation and management measures for north Pacific albacore (Resolutions C-05-02, C-13-03 and C-18-03) are based on maintaining the fishing effort below the 2002-2004 levels. The effort levels in eastern Pacific Ocean for 2017-2019 are 72% and 69% of those in 2002-2004, for vessel-days and number of vessels respectively (Figure F-2).

Figure F-2 Effort in vessel-days and number of vessels for the North Pacific albacore tuna in the eastern Pacific Ocean.

The Working Group is currently undertaking a Management Strategy Evaluation (MSE) for the North Pa-cific albacore stock. The first round of the MSE was concluded and reported during the 4^th ISC ALB MSE workshop in March 2019 (ISC/19/ANNEX/06).

Several operating models were developed, and equal weights was assumed for all alternative operating models when evaluating the HCRs. The results indicated that total allowed effort (TAE) control rules performed better than total allowed catch (TAC). In TAE control, catches adjusted quickly, without management interventions, in response to changes in biomass between assessment periods. Across target reference points (TRPs), there was no single best-performing HCR for all performance metrics (PMs).

Trade-offs were evident between relative catch and relative biomass, catch stability, and odds of no fishery closure. HCRs with the lowest fishing intensity TRP (F50), maintained the population at a higher level than those with the highest fishing intensity TRP (F30), requiring less management intervention and resulting in lower catch variability between years but had the lowest catches.

However, rules with an intermediate TRP of F40 had comparable or higher relative catch than F30 rules despite lower fishing intensity because of fewer closures and higher catch stability. The results of the first round were deemed useful to understand the tradeoffs and potential performance of candidate reference points and harvest control rules by the participants. Additional work was deemed necessary to test all proposed HCR, and to include new operating models. There is a plan to continue into a second round of the MSE. The workshop participants developed a focused list of candidate reference points and harvest control rules to be examined during the 2^nd round of MSE, planned to be completed still in 2020. A 5^th ISC ALB MSE Workshop is planned for the end 2020, when the results of the 2^nd round of the MSE should be presented (ISC/20/PLENARY/02).

The following management objectives for the North Pacific albacore tuna were developed in the context of the MSE process:

Overarching objective: maintain the viability and sustainability of the current NPALB stock and fisheries

1.Maintain spawning biomass above the limit reference point

2.Maintain total biomass, with reasonable variability, around the historical average depletion of total biomass

3.Maintain harvest ratios by fishery (fraction of fishing impact with respect to SSB) at historical average

4.Maintain catches by fishery above average historical catch

5.If a change in total allowable effort and/or total allowable catch occurs, the rate of change should be relatively gradual

6.Maintain F at the target value with reasonable variability

Given the relative stability in the biomass and fishing mortality in recent years, and in view of the 2nd round of MSE, the staff considers that the current resolutions should be continued and that the recommendations from the 4th ISC ALB MSE workshop be adopted. The staff recommends that the management objectives for the North Pacific albacore tuna developed in the context of the MSE process be adopted, then prioritized, ranked, or weighted, to advice the ongoing North Pacific albacore MSE process.