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

EXECUTIVE SUMMARY YFTYFT-6. Management RecommendationsThe status of yellowfin has shown some improvement since the last assessment, which is not surprising in thatcatches and fishing effort have generally declined and there have been small increases in catch rates observed forsome longline fisheries over the past few years. Currently, stock biomass is estimated to be near the ConventionObjective and recent fishing mortality rates somewhat below F MSY . Continuation of current catch levels isexpected to lead to a healthy biomass, somewhat above B MSY , which should provide adequate safeguard againstbiomass falling below the Convention objective as long as fishing effort does not substantially increase. Effortincreases on the order of about 10% above current levels (in order to achieve MSY) would be expected in thelong run to increase yield by only about 1-4% over what could be achieved at current effective effort levels, butwith substantially increased risk of biomass falling below the Convention objective. In addition, the Commissionshould be aware that increased harvest of yellowfin could have negative consequences for bigeye tuna inparticular, and other species caught together with yellowfin in fishing operations taking more than one species.The Committee also continues to recommend that effective measures be found to reduce fishing mortality ofsmall yellowfin, if the Commission wishes to increase long-term sustainable yield.ATLANTIC YELLOWFIN TUNA SUMMARY~130,600 t 1 (124,100-136,500)Maximum Sustainable Yield (MSY)~146,600 t 2 (128,200-152,500)Current Yield 3 (2006) 108,160 tReplacement Yield (2006)Relative Biomass B 2006 / B MSY44Relative Fishing Mortality: F current /F MSYF / 5current F 0.1F / 5current F 20%SPRF / 5current F 30%SPRF / 5current F 40%SPRManagement measures in effect:~ 130,000 t0.96 (0.72-1.22)0.86 (0.71-1.05)1.26 (1.11-1.44)0.81 (0.73-0.93)1.12 (1.01-1.29)1.52 (1.35-1.73)− Effective fishing effort not to exceed 1992 level [Rec. 93-04].− Rec. 04-01, effective 2005. Season/area closure. Although this measure was intended to reduce thecatches of juvenile bigeye tuna, as this is a complete closure, impacts are expected on all tropical tunas.NOTE: F current refers to F 2006 in the case of ASPIC, and the geometric mean of F across 2003-2006 in the case of VPA. As a result of theconstant trend in recruitment estimated by the VPA model, F MAX is used as a proxy for F MSY for VPA results.12345Estimates (with 80% confidence limits) based upon results of the age-structured model (VPA).Estimates (with 80% confidence limits) based upon results of the non-equilibrium production model (ASPIC).The assessment was conducted using the available catch data through 2006. Reports for 2007 should be considered provisional and inthis case includes carryovers from previous years. The preliminary value for 2007 is 96,580 t.Median (25th-75th percentiles) from joint distribution of age-structured and production model bootstrap outcomes considered.Result exclusively from VPA and yield-per-recruit analyses.19