Resource Ecology & Fisheries Management  (cont.)

(2001 Stock Assessment Summary: part 4)
BSAI Greenland Turbot

The current assessment updated last year’s assessment, incorporating new catch and survey information.  The SSC has determined that reliable estimates of B_40%, F_40% and F_35% exist for this stock, and that this stock therefore qualified for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40% and F_35% from the present assessment are approximately 80,000 t, 0.26, and 0.32, respectively.  Projected spawning biomass for 2001 is 132,000 t, placing Greenland turbot in sub-tier “a” of Tier 3.  The maximum permissible value of F_ABC under Tier 3a is 0.26.  Assessment authors recommended that the 2002 ABC should be set at a value substantially less (75%) than the maximum permissible, which results in a 2001 ABC of 8,100 t.  This value was recommended for the following reasons: 1) stochastic trajectory of female spawning biomass and projected catches at maximum F_ABC indicate that the population would decline below F_35% within 3 years; 2) estimated age 1+ biomass has trended downward continually since 1972; 3) annual catches have averaged less than 8,000 t over the last 15 years; and if the maximum permissible ABC of 32,400 t were actually caught, this would constitute the highest catch since 1983, even though spawning biomass in 2002 is projected to be less than half of what it was in 1983.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.

 
BSAI Arrowtooth Flounder

The present assessment updated last year’s assessment with incorporation of new catch and survey information.  This year’s EBS bottom trawl survey resulted in a biomass estimate of 408,800 t, a 20% increase relative to the 2001 trawl survey.  The biomass estimate for the AI is not included in the model due to the low relative catch.  Reliable estimates of B_40%, F_40%, and F_35% exist for this stock; and therefore it qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35%  from the present assessment are 180,100 t, 0.22 and 0.275, respectively.  Given that the projected 2002 female spawning biomass of 423,000 t exceeds B_40%, the ABC and OFL recommendations for 2002 were calculated under sub-tier “a” of Tier 3.  The author recommended setting F_ABC at the F_40% (=0.22) level, which is the maximum permissible level under Tier 3a.  Projected harvesting at the F_40% level gives a 2002 ABC of 113,300 t.  The OFL fishing mortality rate is computed under Tier 3a, F_OFL = F_35% = 0.275, and translates into a 2002 OFL of 137,000 t.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.

 
BSAI Rock Sole

The 2001 assessment incorporated new catch and survey information.  This year’s EBS bottom trawl survey resulted in a biomass estimate of 2,415,000 t, a 14% increase relative to last year’s estimate.  An Aleutian Island trawl survey was performed in 2000 and resulted in a biomass estimate of 46,000 t, which represents only 2% of the BS/AI rock sole combined biomass estimate from the trawl surveys.  The biomass estimate for the AI is not included in the model due to the low relative catch.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock, and therefore this stock qualified for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35%  from the present assessment are 268,000 t, 0.162, and 0.196, respectively.  Given that the projected 2002 spawning biomass of 658,000 t exceeds B_40%, the ABC and OFL recommendations for 2002 were calculated under sub-tier “a” of Tier 3.  The author recommended setting F_ABC at the F_40% (=0.162) level, which is the maximum permissible level under Tier 3a.  Projected harvesting at the F_40% level gives a 2002 ABC of 225,100 t.  The OFL was determined from the Tier 3a formula, where an F_35% value of 0.196 gives a 2002 OFL of 267,900 t.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.  Stock projections for the rock sole stock and several other flatfish stocks continue to show declines due to low recruitment in the last decade.

Cont .>>>

AFSC Quarterly
Research Reports
Oct-Dec 2001