Resource Ecology & Fisheries Management  (cont.)

(2001 Stock Asessment Summary: part 5)
BSAI Flathead Sole

The 2001 assessment was implemented using AD Model Builder as a modeling platform and incorporated new catch and survey information. The 2001 EBS bottom trawl survey biomass estimate was 514,023 t, a 29% increase relative to last year’s estimate.  The 2000 Aleutian Island trawl survey biomass estimate was 8,970 t.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock and, therefore, it is 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 141,903 t, 0.30, and 0.38, respectively. Given that the projected 2002 spawning biomass of 262,402 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% (=0.30) level, which is the maximum permissible level under Tier 3a.  Projected harvesting at the F_40% level gives a 2002 ABC of 82,572 t.

The OFL was determined from the Tier 3a formula, where an F_35% value of 0.38 gives a 2002 OFL of 100,770 t.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.

 
BSAI Other Flatfish Complex

The 2001 assessment was implemented using AD Model Builder as a modeling platform for Alaska plaice only.  The 2001 assessment incorporated new catch and survey information.  The 2001 biomass estimates from the EBS bottom trawl survey were 538,319 t for Alaska plaice and 78,293 t for the remaining species in the “other flatfish” complex.  The biomass estimate for Alaska plaice was 23% higher than the 2000 estimate.  In 2001, excluding Alaska plaice, the species composition of the other flatfish are Dover sole (<1%), rex sole (28%), longhead dab (16%), Sakhalin sole (<1%), starry flounder (55%), and butter sole (1%).  Relative to 2000, Alaska plaice and other flatfish increased.  Projections of Alaska plaice abundance show that the population will gradually decline due to low recruitment.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock complex, 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 132,856 t (Alaska plaice only), 0.279, and 0.344, respectively.  Given that the projected 2002 spawning biomass (Alaska plaice only) of 264,838 t exceeds B_40%, the Plan Team’s ABC and OFL recommendations for 2002 were calculated under sub-tier “a” of Tier 3.  Because 87% of the “other flatfish” category is Alaska plaice and the assessment author calculates plaice separately, the author recommended setting the ABC and OFL for Alaska plaice separately from the other species.  For Alaska plaice, the author recommended F_ABC at the F_40% level (=0.279), which is the maximum allowable under Tier 3a.  Projected harvesting at the F_40% level gives a 2002 ABC of 142,764 t for Alaska plaice.  For the remaining species in the flatfish complex, the author recommended F_ABC at the F_40% level (=0.30), which is the maximum allowable under Tier 3a.  Projected harvesting at the F_40% level gives a 2002 ABC of 18,065 t for “other” nonplaice flatfish.

As with the ABC, the Plan Team recommended separating Alaska plaice from “other” flatfish for OFL. The Plan Team’s OFL was determined from the Tier 3a formula, where for Alaska plaice an F_35% value (=0.35) gives a 2002 OFL of 171,736 t.  For the “other flatfish” species, the author recommended an F_35% value (=0.38) giving a 2002 OFL of 21,832 t.  Model projections indicate that this stock complex is neither overfished nor approaching an overfished condition.

 
BSAI Pacific Ocean Perch

A review of the available data for BSAI Pacific ocean perch (POP) and a series of potential population models were presented to the Plan Team and discussed at the September 2001 meeting.  The Plan Team recommended that a single BSAI model was appropriate for assessment of POP. Motivations for this change include the paucity of data in the EBS upon which to base an age-structured assessment, and uncertainty that the EBS POP represent a discrete stock.  In the combined model, the fishery harvest level and fishery age and length compositions are computed for the entire BSAI area, and the Aleutian Islands survey is used as an index of abundance.  The historical EBS slope surveys are not utilized.

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 140,660 t, 0.048, and 0.057, respectively.  Projected spawning biomass for 2002 is 134,694 t, placing POP in the EBS in sub-tier “b” of Tier 3.  The maximum F_ABC value allowed under Tier 3b is 0.046.  Projected harvesting at a fishing mortality rate of 0.046 gives a 2002 catch of 14,776 t, which is the recommended ABC.  The OFL fishing mortality rate is 0.055 under sub-tier 3b.  Projected harvesting at a fishing mortality rate of 0.055 gives a 2002 catch of 17,510 t, which is the recommended OFL.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.

Cont. >>>

AFSC Quarterly
Research Reports
Oct-Dec 2001