Resource Ecology & Fisheries Management  (cont.)

(2001 Stock Asessment Summary: part 7)
BSAI Squid and Other Species Complex

The squid assessment updated last year’s assessment by incorporating new catch information.  The squid stock is managed under Tier 6, OFL is set equal to the average catch from 1978 through 1995, and ABC is constrained to be no greater than 75% of OFL.  The average catch from 1978 through 1995 was 2,624 t.  The maximum permissible value of ABC for 2001 therefore is 1,970 t, which is the Plan Team’s recommended value.

The  “other species” assessment is an update of last year’s assessment, incorporating new catch and survey biomass information.  For the 2002 fishing year, the author’s recommended ABC for the other species complex was calculated as 0.75 times the average catch 1978-95, or 19,320 t.  The author recommended OFL for the other species complex in the year 2002 be calculated as the average catch from 1978 to  1995, or 25,760 t.  The NPFMC SSC recommended that this strategy be reviewed.

 
GOA Pollock

A Generalized Linear Model (GLM) analysis of historical trawl survey data (1961-82) produced indices of pollock abundance prior to the start of the NMFS triennial survey in 1984.  Incorporation of these indices and the information from a comparative trawling experiment between an ADF&G 400-mesh eastern trawl and a NMFS Poly-Nor’eastern trawl made it possible to extend the time series of pollock biomass and recruitment back to 1961.  Model results suggest that population biomass in 1961, prior to large-scale commercial exploitation of the stock, may have been the lowest observed.  Major increases in pollock abundance occurred prior to the 1977 regime shift, suggesting forcing by some other aspect of the environment or ecosystem.   The occurrence of large fluctuations in pollock abundance without large changes in direct fishing impacts suggests a need for conservative management.  If pollock abundance is controlled primarily by the environment, or through indirect ecosystem effects, it may be difficult to reverse population declines, or to achieve rebuilding targets should the stock become depleted.

Estimated spawning biomass in 2002 is 158,300 t, a decrease of 22% from last year’s estimate for 2001, and a decrease of 8% from last year’s projection for 2002.  Lower model estimates of biomass in 2002 are primarily due to lower than expected biomass from the 2001 NMFS trawl survey (65% decrease from the 1999 survey) and low abundance of spawning adults in the 2001 Shelikof Strait EIT survey (49% decrease from the 2000 survey).  Spawning biomass in 2002 is estimated to be 26% of unfished.  Under the new Reasonable and Prudent Alternatives (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 biomass.  Spawning biomass is projected to be below the B_40% value of 245,000 t.  This places Gulf pollock in Tier 3b. The ABC for 2002 was 53,490 t for the Western, Central, and West Yakutat areas.

For 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, 2002 ABC is 6,460 t, based on exploitable biomass of 28,710 t as derived from CPUE data during the 1999 Gulf trawl survey and a natural mortality estimate of 0.30.  The OFL is 8,610 t.  The pollock catch in the pooled Southeast Outside and East Yakutat areas never exceeded 100 t during 1991-2000.

 
GOA Pacific Cod

The 2001 Pacific cod assessment incorporated several new types of data including:  size composition from 2000 and January-August 2001 commercial fisheries, size composition from the 2001 GOA bottom trawl survey, and biomass estimates from the 2001 GOA bottom trawl survey.  The 2001 GOA bottom trawl survey biomass estimate was 256,025 t for the Western and Central areas which was down 10% from the 1999 estimate for the same areas.

The Bayesian meta-analysis which  formed the basis for risk-adverse ABC recommendations in the 1996-99 assessments was not performed for the 2001 assessment.  Similar to procedures used in 2000, the ratio between the recommended F_ABC and F_40% estimate given in the 1999 assessment (0.87) was assumed to be an appropriate factor by which to multiply the 2001 maximum permissible F_ABC to obtain a recommended 2001 F_ABC.

The estimated 2002 spawning biomass for the GOA stock was 82,000 t, down 13% from last year’s estimate for 2001.  The recommended 2002 ABC for the GOA stock was 57,600 t, down 15% from last year’s recommendation for 2001.  The OFL for the GOA Pacific cod stock was 77,100 t.

Cont. >>>

AFSC Quarterly
Research Reports
Oct-Dec 2001