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(SAFE Summaries cont.)

GOA Pollock

The 2002 GOA pollock assessment was updated by incorporating new catch, age composition, biomass estimates, and maturity data into the assessment. The 2002 EIT trawl survey of the Shumagin Islands provided a biomass estimate of 135,600 t. The 2002 Shelikof Strait biomass estimate of age-2+ fish was 229,100 t, a decrease of 38% from the 2001 biomass estimate. The biomass of adult fish in Shelikof Strait (38,037 t) was lower than expected. An additional 82,100 t of pollock were encountered along the shelf break during exploratory transects. The ADF&G trawl survey biomass estimate was 96,237 t, an 11% increase from the 2001 biomass estimate. Evidence from these surveys indicates that the 1999 year class will be above average.

The stock assessment model was unchanged in 2002. Model exploration focused on approaches to modeling the survey time series, in particular the winter echo integration-trawl (EIT) surveys. The model estimate of 2003 spawning biomass was 177,070 t, of which 28% is unfished. Under the new Reasonable and Prudent Alternative (RPA) control rule approved by the Council, pollock fishing in the Gulf of Alaska would have to be stopped if biomass declines to 20% of unfished. Spawning biomass is projected to be below the B40% value of 240,000 t. This places GOA pollock in Tier 3b. The ABC for 2003 was 49,590 t for the Western, Central, and West Yakutat areas. A preliminary evaluation of the probability that the stock is below the B20% threshold was conducted. This analysis indicates that there is only a 2% probability of the stock being below the B20% threshold in 2003.

For walleye pollock in Southeast Alaska (East Yakutat and Southeastern areas), the ABC recommendation is unchanged at 6,460 t. Pollock in the Southeast Outside and East Yakutat areas fall into Tier 5. Under the Tier 5 approach, the 2003 ABC is 6,460 t, based on exploitable biomass of 28,710 t as derived from CPUE data during the 1999 GOA trawl survey and a natural mortality estimate of 0.30. The OFL is 8,610 t.

GOA Pacific Cod

The 2002 Pacific cod assessment incorporated several new types of data including size composition from 2001 and January-August 2002 commercial fisheries and catch from the 2001 fisheries.

The Bayesian meta-analysis, which has formed the basis for risk-adverse ABC recommendations in the 1996- 99 assessments, was not performed for the 2002 assessment. Similar to procedures used in 2001, the ratio between the recommended FABC and F40% estimate given in the 1999 assessment (0.87) was assumed to be an appropriate factor by which to multiply the 2003 maximum permissible FABC to obtain a recommended 2003 FABC.

The estimated 2003 spawning biomass for the GOA stock was 88,300 t, up about 8% from last year's estimate for 2002. The recommended 2003 ABC for the GOA stock was 52,800 t, down about 8% from last year's recommendation for 2002. The OFL for the GOA Pacific cod stock in 2003 was 70,100 t.

GOA Flatfish

Table 5.  Summary of ABC by management area for Gulf of Alaska flatfish species (except flathead sole) for 2003
  Western Central Western Yakutat Eastern Yakutat/
Southeast Outside
Deep-water       184    2,221 1,326 1,146    4,877
Rex sole    1,277    5,537 1,599 1,053    9,466
Shallow water 23,483 21,743 1,160 2,960 49,349

The flatfish group is subdivided into deep-water flatfish, rex sole, shallow-water flatfish, and flathead sole. The projected 2003 exploitable biomass for each category is based on a delay difference model that includes estimates of growth, natural mortality, and recruitment, as well as biomass estimates from the 1996 and 2001 bottom trawl surveys. ABC and OFL were calculated by species, with individual species identified as Tier 4, 5, or 6 depending upon the available data. The 2001 GOA bottom trawl survey biomass was used as the current biomass for calculation of ABC for deep water, shallow water and rex sole. An age-structured model was used to estimate ABCs for flathead sole (see table 1. above).

GOA Arrowtooth Flounder

The 2002 stock assessment for arrowtooth flounder was updated with new catch information. An age-structured model developed with AD Model Builder software was utilized for this assessment. Similar to the previous assessment, the model accommodated a higher proportion of females in the larger size intervals of both survey and fishery data by giving males a higher natural mortality rate than females.

Reliable estimates of biomass, B40%, F40% and F35% exist placing arrowtooth flounder in Tier 3. Spawning biomass in 2003 was 1,117,490 t. This estimate was greater than B40% (494,495 t) so harvest recommendations were based on sub-Tier 3a. Under sub-Tier 3a, the 2003 ABC of 155,139 t was derived by applying a F40% (0.140) fishing mortality rate.

 GOA Atka Mackerel 

YEAR        ABC
2003        600

GOA Thornyheads

In 2002, the thornyhead assessment was updated with 2001 harvest levels by gear and relative population numbers from the 2002 sablefish longline survey. Alternate models examined assumptions regarding natural mortality and length at age. The author recommended ABC, OFL, and spawning stock biomass levels were 2,555 t, 3,051 t, and 23,549 t, respectively. The Plan Team recommended an ABC of 2000 t to compensate for uncertainty in the natural mortality estimate.

By Anne Hollowed.


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