Status of Stocks & Multispecies Assessment Program
Groundfish Stock Assessments for 2009: Gulf of Alaska (GOA) Species
GOA Pollock: The 2008 Shelikof Strait echo integration-trawl (EIT) survey was the first conducted using the NOAA ship Oscar Dyson. The 2008 biomass estimate for Shelikof Strait was 15% higher than the 2007 estimate.
In winter of 2007, a vessel comparison experiment was conducted between the NOAA ship Miller Freeman (MF) and the Oscar Dyson (DY), which obtained an DY/MF ratio of 1.132. These results suggest that biomass was relatively constant from 2007 to 2008. Biomass estimates of Shelikof Strait fish ≥43 cm (a proxy for spawning biomass) decreased by 52% from the 2007 estimate, apparently due to below average recruitment to the spawning population. However, the 2008 Alaska Department of Fish & Game (ADF&G) crab/groundfish survey biomass estimate increased 9% from 2007.
Despite the significant difference in the ratio of pollock backscatter between the Miller Freeman and Oscar Dyson, the impact on assessment results and recommended ABCs was minor regardless of the modeling approach.
The 2009 spawning biomass and ABCs varied 5%-7% across different model configurations, while population biomass varied by about 3%. The assessment results provided an estimated 2009 spawning biomass of 132,810 t, or 22% of unfished spawning biomass.
Projections in stock estimates in recent years generally show increases that have not been realized. This could be due to a number of factors including the use of average recruitment in the current projection while below average recruitment is occurring, and juvenile natural mortality may be higher than assumed. While short-term outlooks indicate that the stock should increase, added conservation measures were made in recommending an ABC level for GOA pollock.
GOA Pacific Cod: Extensive work on the GOA Pacific cod model has occurred during the past year with draft assessments presented at both the September and November Plan Team meetings.
Changes to the input data include updated catch data; recompilation of the pre-1990 fishery size composition data; updating the ageing error matrix; recompilation of the weight-at-length time series, updating the 2007 seasonal catch-per-unit-effort data from the longline, pot, and trawl fisheries; and splitting each trawl survey abundance estimate and size composition into fish smaller than 27 cm (referred to as the "sub-27" survey) and fish 27 cm and larger (referred to as the "27-plus" survey).
New data to the model included age composition and length-at-age data from the 1987, 1990, and 1993 GOA shelf bottom trawl surveys and preliminary catch rates for the 2008 longline and pot fisheries. The Council-selected model resulted in a 2009 spawning biomass of 88,000 t, or 34% of unfished spawning biomass. Results also suggested that the spawning biomass will increase dramatically in subsequent years because of the 2006 year class, which was estimated to be the highest on record.
The extent of the rate of increase depends on the magnitude of this year class, which was extremely uncertain being based solely on length frequencies collected in the 2007 trawl survey. The 2009 GOA trawl survey will be critical to better estimate the magnitude of the 2006 year class.
GOA/BSAI Sablefish: The survey abundance index decreased 2% from 2007 to 2008, a change which follows a 14% decrease from 2006 to 2007. The fishery abundance index was up 5% from 2006 to 2007.
The spawning biomass was projected to be similar from 2008 to 2009, but is expected to decline through 2012. The projected 2009 spawning biomass is 36% of unfished biomass with the 1997 year class representing an important but waning contributor to the population. The projected spawning biomass (combined areas) for 2009 is 103,127 t (90% of B40%).
Highlights of issues for sablefish include the impact of sperm whale depredation on the longline survey and the fact that an external stock assessment review is planned for 2009. The Alaska-wide recommended 2009 ABC is 16,080 t, approximately 11% lower than the 2008 level. Based on survey data, the relative decline is greater in the GOA than for the BSAI region, and this affects the spatial allocation of the available quota.
GOA Other Species: The other species complex in the GOA contains the following species groups: sculpins, squids, sharks, and octopus. In the past, assessments for these species in the GOA were done periodically, since ABCs and OFLs were not specified and the assessments were provided as appendices to the SAFE report.
The TAC calculation for other species (previously TAC = 5% of the sum of target TACs) was modified in 2005 such that the Council may recommend a TAC at or below 5% of the sum of the target species TACs during the annual specifications process. Amendment 79 to the GOA FMP provides for the specification of ABC and OFL for the other species complex.
This year full assessments were presented in the SAFE report to be used for the setting of harvest specifications for the other species complex, which are the sums of the ABCs and OFLs of the individual species groups. The recommended 2009 ABC for this group is 6,540 t.
