REPORT OF THE STANDING COMMITTEE ON RESEARCH ... - Iccat

EXECUTIVE SUMMARY BFTinformation that is being collected. If the curve changes substantially, it may impact the assessment results aswell as management benchmarks.BFTW-4. OutlookA medium-term (12-year) outlook evaluation of changes in spawning stock size and yield over the remainingrebuilding period under various management options was conducted. Future recruitment was assumed tofluctuate around two alternative scenarios: (i) average levels observed for 1976-2004 (70,000 recruits, the lowrecruitment scenario) and (ii) levels that increase as the stock rebuilds (MSY level of 160,000 recruits, the highrecruitment scenario). The Committee has no strong evidence to favor either scenario over the other and notesthat both are reasonable (but not extreme) lower and upper bounds on rebuilding potential.The outlook for bluefin tuna in the West Atlantic with the low recruitment scenario (BFTW-Figure 4) is similarto that from the 2006 assessment. A total catch of 2,100 t is predicted to have at least a 50% chance of achievingthe convention objectives of preventing overfishing and rebuilding the stock to MSY levels by 2019, the targetrebuilding time. The outlook under the high recruitment scenario (BFTW-Figure 4) is more pessimistic sincethe rebuilding target would be higher; a total catch of less than 1,500 t is predicted to stop overfishing in 2009,but the stock would not be expected to rebuild by 2019 even with no fishing.BFTW-Table 1 summarizes the estimated chance that various constant catch policies will allow rebuildingunder the high and low recruitment scenarios for the base-case. The low recruitment scenario suggests that catchlevels of 2,400 t will have about a 50% chance of rebuilding the stock by 2019 and catches of 2,000 t or lowerwill have greater than a 75% chance of rebuilding. If the high recruitment scenario is correct, then the westernstock will not rebuild by 2019 even with no catch, although catches of 1,500 t or less are expected toimmediately end overfishing (50% chance) and initiate rebuilding (BFTW-Table 2).Among the alternative models examined by the Committee, the option that excluded the Canadian Gulf of St.Lawrence index was examined further, due to the considerations of possible resource re-distribution, and theobservation that the recent high values were difficult to reconcile with other available fisheries data, and couldreflect the impact of a single or a limited number of strong year-classes. The levels of catch that lead torebuilding with that alternative model are lower; 1,800 t will have about a 50% chance and 1,500 t will have a75% chance.The Committee notes that considerable uncertainties remain for the outlook of the western stock, including theeffects of mixing and management measures on the eastern stock.BFTW-5. Effects of current regulationsCatches of western bluefin have been below the TAC since 2003, although that was not always the case prior tothen (Figure BFTW-1). The estimated percentage of fish less than 115cm in the catch has been less than 8% ofthe TAC from 1992 to 2006, although this percentage increased in 2007 to about 11% of TAC.The Committee previously noted that Recommendation 06-06 was expected to result in a rebuilding of the stocktowards the convention objective, but also noted that there has not yet been enough time to detect withconfidence the population response to the measure.BFTW-6. Management recommendationsIn 1998, the Commission initiated a 20-year rebuilding plan designed to achieve Bmsy with at least 50%probability. The current assessment indicates that the stock has not yet rebuilt as projected under the planinitially. The 2007 SSB is estimated to be 7% below the level of the Plan’s first year.Based on a strict interpretation of the base case projections and the Western Atlantic Rebuilding Plan [Rec. 98-07], the Commission is faced with TAC options that range between 2,400 t and zero depending on its choice ofrecruitment scenarios and choice of the probability of rebuilding. The Committee notes that making decisionsbased on the low recruitment scenario when in fact the high recruitment scenario is true, could be riskier in terms77