RESOURCE ECOLOGY & FISHERIES MANAGEMENT (REFM) DIVISION
(SAFE Summaries cont.)

BSAI Yellowfin Sole

The 2002 assessment incorporated new catch and survey information. This year's EBS bottom trawl survey resulted in a biomass estimate of 2,003,400 t, an increase of 8% from last year's survey. As in previous years, the catchability of yellowfin sole is modeled as a linear function of water temperature.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock and, therefore, qualify 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 385,000 t, 0.115, and 0.138, respectively. Given that the projected 2003 spawning biomass of 452,800 t exceeds B_40%, the ABC and OFL recommendations for 2003 were calculated under sub-tier "a" of Tier 3. The author recommended setting F_ABC at the F_40% (=0.115) level, which is the maximum permissible level under Tier 3a. Projected harvesting at the F_40% level gives a 2003 ABC of 113,600 t. The OFL was determined from the Tier 3a formula, where an F_35% value of 0.138 gives a 2003 OFL of 134,800 t. Model projections indicate that this stock is neither overfished nor approaching an overfished condition. Stock projections show the yellowfin sole stock will continue to decline despite low exploitation rates. The decline is due to the low recruitment in the last decade.
 

BSAI Greenland Turbot

The current assessment updated last year's assessment, incorporating new catch and survey information. The 2002 survey biomass estimates for the EBS shelf and slope were 21,616 t and 27,589 t, respectively. The 2002 survey biomass estimate for the Aleutian Islands was 9,891 t.

In 2002, research on an alternative assessment model was presented. Part of this research involved incorporation of additional data published in Russian reports. 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 54,000 t, 0.26, and 0.32, respectively. Projected spawning biomass for 2003 was 67,800 t, placing Greenland turbot in sub-tier "a" of Tier 3. The estimates of current spawning biomass and B_40% were lower than previous years because the new Eastern Bering Sea slope survey biomass estimates were included in the assessment. The maximum permissible value of F_ABC under Tier 3a is 0.26. Assessment authors recommended that the 2003 F_ABC should be based on the 5-year average fishing mortality, resulting in a 2003 ABC of 5,880 t. This value was recommended because of uncertainty in the survey biomass estimates. The recommended OFL for this stock was 17,800 t.

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. The 2002 EBS bottom trawl survey resulted in a biomass estimate of 355,100 t, a 13% decrease relative to the 2001 trawl survey. In 2002, RACE conducted an assessment of the EBS slope. The biomass estimate for arrowtooth flounder derived from this new survey was 61,200 t. The 2002 biomass estimate for the Aleutian Islands stock was 88,700 t. However, this biomass estimate was not included in the model.

The new slope survey biomass estimates were incorporated into the model by configuring q for the shelf and slope to be equal to 0.87 and 0.13, respectively. These values reflect the proportion of the EBS stock observed in the shelf and slope regions.

Model runs were made with sex-specific natural mortality rates. The preferred model fixed male natural mortality rate at 0.281 and the female natural mortality rate at 0.2. This model configuration was consistent with the author's hypothesis that differences in sex ratios in observed catches is due to differential sex-specific survival rates.

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 206,300 t, 0.30 and 0.38, respectively. Given that the projected 2003 female spawning biomass of 436,400 t exceeds B_40%, the ABC and OFL recommendations for 2003 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 2003 ABC of 112,300 t.

The OFL fishing mortality rate is computed under Tier 3a, F_OFL = F_35% = 0.38, and translates into a 2003 OFL of 139,000 t. Model projections indicate that this stock is neither overfished nor approaching an overfished condition.
 

BSAI Rock Sole

The 2002 assessment incorporated new catch and survey information. This year's EBS bottom trawl survey resulted in a biomass estimate of 1,901,800 t, a 21% decrease relative to the 2001 estimate. An AI trawl survey was performed in 2002 and resulted in a biomass estimate of 57,700 t, which represents only 3% of the BSAI rock sole combined biomass estimate from the trawl surveys.

Survey catchability was incorporated into the 2002 stock assessment to account for herding and temperature effects on rock sole capture. This results in a marked reduction in the present and historical biomass estimates of BSAI rock sole.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock, which therefore qualifies rock sole 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 158,600 t, 0.176, and 0.213, respectively. Given that the projected 2003 spawning biomass of 303,100 t exceeds B_40%, the ABC and OFL recommendations for 2003 were calculated under sub-tier "a" of Tier 3. The author recommended setting F_ABC at the F_40% (=0.176) level, which is the maximum permissible level under Tier 3a. Projected harvesting at the F_40% level gives a 2003 ABC of 110,200 t. The OFL was determined from the Tier 3a formula, where an F_35% value of 0.213 gives a 2003 OFL of 131,700 t. Model projections indicate that this stock is neither overfished nor approaching an overfished condition. Stock projections for the rock sole stock continue to show declines, as do several other flatfish stocks, due to the low recruitment in the last decade.
 

BSAI Flathead Sole

The 2002 assessment incorporated new catch and survey information. The 2002 EBS bottom trawl survey biomass estimate was 574,946 t, a 12% increase relative to last year's estimate. The 2002 AI trawl survey biomass estimate was 9,894 t.

The 2002 assessment was implemented using AD Model Builder as a modeling platform. The model was configured as a split-sex population. Age compositions were developed for each sex to account for differential growth across sexes.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock, and therefore, 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 124,289 t, 0.286, and 0.355, respectively. Given that the projected 2003 spawning biomass of 224,526 t exceeds B_40%, the ABC and OFL recommendations for 2003 were calculated under sub-tier "a" of Tier 3. The author recommended setting F_ABC at the F_40% (=0.286) level, which is the maximum permissible level under Tier 3a. Projected harvesting at the F_40% level gives a 2003 ABC of 66,410 t. However, it is unlikely that the total ABC will be taken in 2003 because the total catch of flathead sole has been well below the ABC for several years.

The OFL was determined from the Tier 3a formula, where an F_35% value of 0.355 gives a 2003 OFL of 80,563 t. Model projections indicate that this stock is neither overfished nor approaching an overfished condition.
 

BSAI Alaska Plaice

The 2002 assessment for Alaska plaice incorporated new catch and survey information. The 2002 biomass estimate from the EBS bottom trawl survey was 424,971 t for Alaska plaice, a 27% decrease from the 2001 survey biomass estimate.

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 130,888 t, 0.279, and 0.344, respectively. Given that the projected 2003 spawning biomass of Alaska plaice (255,676 t) exceeds B_40%, the Plan Team's ABC and OFL recommendations for 2003 were calculated under sub-tier "a" of Tier 3. 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 2003 ABC of 137,015 t for Alaska plaice. It is unlikely that the total ABC will be taken in 2003 because the total catch of Alaska plaice has been well below the ABC for several years. Stock projections of Alaska plaice show that the population will gradually decline due to low recruitment.

The OFL for Alaska plaice was determined from the Tier 3a formula, where, for F_35% value (=0.344) gives a 2003 OFL of 164,822 t. Model projections indicate that Alaska plaice is neither overfished nor approaching an overfished condition.

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AFSC Quarterly
Research Reports
Oct.-Dec. 2002