RESOURCE ECOLOGY & FISHERIES MANAGEMENT (REFM) DIVISION

STATUS OF STOCKS AND MULTISPECIES ASSESSMENT PROGRAM:

2002 Stock Assessment Summary

The Status of Stocks and Multispecies Assessment Program (SSMA) completed stock assessments for major groundfish stocks in the Bering Sea, Aleutian Islands, and Gulf of Alaska. (The information provided in this report summarizes the 2002 stock assesments. Complete assessments are available from the Status of Stocks and Multispecies Assessment Program's website.) Information from a variety of sources were used including survey biomass estimates provided by the RACE Division, fishery catch estimates from the NMFS Alaska Regional Office, fishery dependent biological samples from the REFM Observer Program and fishery and survey age composition data from the REFM Age and Growth Program. Final SAFE (Stock Assessment and Fishery Evaluation) reports were prepared for the North Pacific Fishery Management Council (NPFMC) meetings. The NPFMC used the assessments to recommend levels of Acceptable Biological Catch (ABC) for the 2003 fishing season.

Scientists from the SSMA Program participated in preparation of many of the assessment chapters for the Gulf of Alaska and Bering Sea/Aleutian Islands regions. Scientists from the Auke Bay Laboratory, the RACE Division, and the Alaska Department of Fish and Game also authored or contributed to the development of the SAFE chapters.

In 2002, 15 stocks or stock complexes in the Bering Sea/Aleutian Islands (BSAI) were assessed: walleye pollock, Pacific cod, yellowfin sole, Greenland turbot, rock sole, flathead sole, arrowtooth flounder, Alaska plaice, other flatfish (includes 16 species of flatfish), BSAI Pacific ocean perch, other red rockfish, other rockfish, sablefish, Atka mackerel, and "other species" (see Table 1 below for species included in stock complexes). With the exception of sablefish, SSMA stock assessment authors were lead authors for all BSAI assessments. In the Gulf of Alaska (GOA), 10 stocks or stock complexes were assessed: walleye pollock, Pacific cod, arrowtooth flounder, other flatfish, Pelagic shelf rockfish, slope rockfish, demersal shelf rockfish, thornyhead, sablefish, and Atka mackerel. SSMA authors were the primary authors on 8 of the 10 GOA assessment chapters. Major findings for selected assessments are summarized below, grouped by management area and species.

The values presented below reflect information found in the SAFE documents developed by the NPFMC's Plan Teams for groundfish fisheries in the GOA and BSAI. It should be noted that the Plan Team ABC and Total Allowable Catch (TAC) recommendations are reviewed by the NPFMC advisory bodies and the Council recommends the final TAC. Thus, the values presented below may differ from the final Council recommendations. For information final groundfish specifications, please consult the NPFMC's web page at www.fakr.noaa.gov/npfmc.
 

BSAI Walleye Pollock

This year's walleye pollock assessment features new data from the 2002 bottom trawl survey, the 2002 echo-integration trawl (EIT) survey and from the 2001 fishery. The 2002 bottom trawl survey estimated a biomass of 4,820,000 metric tons (t). The 2002 EIT survey estimated biomass was 3,600,000 t. Pollock otoliths collected during the bottom trawl survey were examined for age determination, and numbers-at-age from this survey were estimated and used in the stock assessment. Length frequency data from the EIT survey were applied to an age-length key constructed from the bottom- trawl survey data to derive a preliminary age composition for that survey. Pollock age and size composition data were used to estimate the 2001 catch-at-age. Estimates of weight-at-age for 2001 were also added to the assessment.

In previous years, the SSC determined that reliable estimates of B_MSY and the probability density function for F_MSY exist for this stock, and that eastern Bering Sea (EBS) walleye pollock therefore qualified for management under Tier 1. The maximum permissible value of fishing mortality (F_ABC) under Tier 1a is based on the harmonic mean value of F_MSY. This translates into a 2003 catch of 2,327,000 t. Under Tier 1a, the 2003 overfishing level is 3,532,000 t corresponding to a fishing mortality rate of F_MSY. The authors noted that a fixed catch of 1,400,000 t would maintain the stock above B_40% level of spawning in the near term and greatly reduced future yield variability.

The 2002 bottom trawl survey of the AI region resulted in a biomass estimate of 175,283 t, an increase from the previous estimate from the 2000 survey. Aleutian and Bogoslof Islands pollock qualify for management under Tier 5. For the AI region, this gives an ABC and Over Fishing Level (OFL) of 39,438 t and 52,585 t, respectively. For Bogoslof Island pollock, the 2002 EIT survey of the region resulted in a biomass estimate of 227,000 t. The adjusted value (considering that this region is treated as an index site for the Bering Sea basin or Donut Hole stock) for ABC is 4,074 t.
 

BSAI Pacific Cod

The 2002 assessment updated last year's assessment, incorporating new catch and survey information. This year's EBS bottom trawl survey resulted in a biomass estimate of 616,923 t, a 26% decrease from last year's estimate. The Aleutian Islands were surveyed in 2002; the biomass estimate was 82,853 t, representing a decrease of 39% from the 2000 estimate. The 2003 estimate of Pacific cod age 3+ abundance was 1,680,000 t. Projected 2003 spawning biomass for the BSAI stock was 423,000 t, essentially unchanged from last year's estimate for 2002. The SSC has determined that reliable estimates of B_40%, F_40%, and F_35% exist for this stock, and that this stock therefore qualifies for management under Tier 3 of the BSAI Groundfish Fishery Management Plan (FMP). The recommended 2003 ABC and OFL for the BSAI stock was 245,000 and 324,000 t, respectively.The Bayesian meta-analysis, which has formed the basis for a risk-averse ABC recommendation in each of the 1996-99 assessments, was not performed for the present assessment. The ratio between the recommended F_ABC and F_40% given in the 1999 assessment (0.87) was assumed to be an appropriate factor by which to multiply the 2003 maximum permissible F_ABC to obtain a recommended 2003 F_ABC. The recommended OFL was determined from the Tier 3 formula times 0.87. Model projections indicate that this stock is neither overfished nor approaching an overfished condition.

An alternative model configuration with a separate set of selectivity schedules for year 2000 and beyond was evaluated in the 2002 assessment.

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AFSC Quarterly
Research Reports
Oct.-Dec. 2002