Marine Ecology and Stock Assessment Program
Groundfish Stock Assessments
This quarter three full Stock Assessment and Fishery Evaluation (SAFE) reports and eight executive summary SAFE reports were prepared by scientists from ABL's Marine Ecology and Stock Assessment (MESA) program. For each assessment, the results were presented to the North Pacific Fishery Management Council's Groundfish Plan Teams in November and also reviewed by the Council's Scientific and Statistical Committee in December. The Council used these assessments as the primary source for determining levels of Total Allowable Catch (TAC) in 2013. Full assessments were prepared for Alaska sablefish, Bering Sea/Aleutian Islands (BSAI) sharks, and Alaska grenadiers. Executive summaries were prepared for species in the Gulf of Alaska (GOA): Pacific ocean perch, thornyheads, northern rockfish, dusky rockfish, rougheye/blackspotted rockfish, shortraker rockfish, "other rockfish,” and sharks.
The sablefish longline survey abundance index decreased 21% from 2011 to 2012 following an 18% increase from 2008 to 2011. The fishery abundance index was stable from 2010 to 2011 (the 2012 data are not available yet) following a decrease of 9% from 2009 to 2010. There are signs of a strong incoming 2008 year class based on longline survey data. Spawning biomass is projected to decrease from 2013 to 2017 and then stabilize. The strong 2000 year class is the largest contributor, comprising 20% of the spawning biomass in 2013. The Alaska sablefish stock assessment model was unchanged from 2011 and showed a 6% decrease in TAC recommendations as a result of the decrease in the 2012 longline survey index that is somewhat offset by the relatively high survey years in 2010 and 2011.
Research on depredation effects on the sablefish survey index from both killer whales and sperm whales continues. Thus far there has been success in determining the effects of whale depredation on the index. Sperm whale effects may be useful to incorporate as a correction factor in the index, but killer whale effects may be too variable to use.
A detailed analysis of sablefish fishery catch rate data is being conducted in collaboration with a postdoctoral researcher to better capture abundance trends from fishery data. A “core fleet” that has fished for at least 15 years has been identified. The effects of spatial and depth distributions of the fishery and other species (Greenland turbot, Pacific halibut, Pacific cod, and grenadiers) catch rates on the index are being explored.
Although there are seven species of grenadiers in Alaska, the giant grenadier is the most abundant species and is by far the most common grenadier caught in commercial fisheries and surveys. Thus, stock assessments focus on giant grenadier. A new method of estimating giant grenadier biomass in the Aleutian Island (AI) was used. This method incorporated both longline and trawl survey data to extrapolate trawl survey biomass estimates to deep water (500 – 1,000 m). The new method provided lower estimates of biomass than previously reported, but trends are similar between the old and new method. Presently, grenadiers are not included in the Fishery Management Plans (FMPs). ABL scientists continue to recommend that the Council include grenadiers in both the BSAI and GOA FMPs so that annual catch limits can be established.
For BSAI sharks, biomass estimates from surveys are not considered reliable, and there is limited biological information. Thus, TAC recommendations are determined based on a calculation that uses historical catch history. A comparison of potential catch quotas was made between two different methods of estimating shark catch. The first method used official catch estimates as provided by the Catch Accounting System, and the second method used catches that incorporated the Halibut Fishery Incidental Catch Estimates (HFICE) that attempt to account for unobserved shark bycatch in the halibut fishery. ABL scientists recommended that catch quotas continue to be determined using the first method primarily because of uncertainties associated with the HFICE.
A stock structure analysis was completed for sharks in the GOA and BSAI. The shark complex has a mix of three main species (spiny dogfish, Pacific sleeper shark, and salmon shark), each with different life histories. There is considerable difficulty in evaluating whether there is a need for additional spatial or species-specific management of sharks because data are limited.
A stock structure analysis was also completed for Pacific ocean perch in the GOA. Given the available evidence on stock structure, the current resolution of spatial TACs could potentially be increased to smaller areas (five areas instead of three), without imposing quotas that are onerously small for management.
For more information about these assessments, see the Status of Stocks & Multispecies Assessment Program's article "Update on Groundfish Stock Assessment for the 2013 Fishery" in the Resource Ecology and Fishery Management (REFM) Division section of this issue of the Center's Quarterly Report or the stock assessment reports on the AFSC website.
By Jon Heifetz.