Science & Data

The "flatfish" species complex previous to 1990 was managed as a unit in the Gulf of Alaska (GOA). It included the major flatfish species inhabiting the region, with the exception of Pacific halibut. The North Pacific Fishery Management Council divided the flatfish assemblage into four categories for management in 1990; "shallow flatfish" and "deep flatfish", flathead sole and arrowtooth flounder. This classification was made because of significant differences in halibut bycatch rates in directed fisheries targeting the shallow-water and deepwater flatfish species. Arrowtooth flounder, because of its present high abundance and low commercial value, was separated from the group and managed under a separate acceptable biological catch (ABC). Flathead sole were likewise assigned a separate ABC since they overlap the depth distributions of the shallow-water and deepwater groups. In 1993, rex sole was split out of the deepwater management category because of concerns regarding the bycatch of Pacific ocean perch in the rex sole target fishery.

Gulf of Alaska (GOA) Atka mackerel has been moved to a biennial stock assessment schedule to coincide with the availability of new survey data from the biennial trawl survey. A full assessment was presented in 2011, which included data from the 2011 GOA bottom trawl survey. On alternate (even) years we present an executive summary with updated catch, last year’s key assessment parameters, any significant new information available in the interim, and projections for this year. Although a survey was conducted in 2013, we provide an expanded executive summary with updated catch and new survey information as described below.

Arrowtooth flounder have historically been assessed on an annual basis in the Bering Sea/Aleutian Islands region to coincide with the annual Bering Sea shelf multispecies groundfish trawl survey conducted each summer. In 2012, Bering Sea/Aleutian Islands (BSAI) arrowtooth flounder was moved to a biennial assessment schedule to coincide with the frequency of trawl surveys in the Aleutian Islands (AI) and the eastern Bering Sea (EBS) slope. These surveys occur in even years, and for these years a full assessment of Arrowtooth flounder in the BSAI area is conducted.

The National Standard Guidelines for Fishery Management Plans published by the National Marine Fisheries Service (NMFS) require that a stock assessment and fishery evaluation (SAFE) report be prepared and reviewed annually for each fishery management plan (FMP). The SAFE reports are intended to summarize the best available scientific information concerning the past, present, and possible future condition of the stocks and fisheries under federal management. The FMPs for the groundfish fisheries managed by the Council require that drafts of the SAFE reports be produced each year in time for the December North Pacific Fishery Management Council (Council) meetings. The SAFE report for the Gulf of Alaska (GOA) groundfish fisheries is compiled by the Plan Team for the Gulf of Alaska Groundfish FMP from chapters contributed by scientists at NMFS Alaska Fisheries Science Center (AFSC) and the Alaska Department of Fish and Game (ADF&G). The stock assessment section includes recommended acceptable biological catch (ABC) levels for each stock and stock complex managed under the FMP. The ABC recommendations, together with social and economic factors, are considered by the Council in determining total allowable catches (TACs) and other management strategies for the fisheries.

The yellowfin sole (Limanda aspera) is one of the most abundant flatfish species in the eastern Bering Sea (EBS) and is the target of the largest flatfish fishery in the world. They inhabit the EBS shelf and are considered one stock. Abundance in the Aleutian Islands region is negligible. Yellowfin sole are distributed in North American waters from off British Columbia, Canada, (approx. lat. 49o N) to the Chukchi Sea (about lat. 70o N) and south along the Asian coast to about lat. 35o N off the South Korean coast in the Sea of Japan. Adults exhibit a benthic lifestyle and occupy separate winter, spawning and summertime feeding distributions on the eastern Bering Sea shelf. From over-winter grounds near the shelf margins, adults begin a migration onto the inner shelf in April or early May each year for spawning and feeding. In recent years, the directed fishery has typically occurred from late winter through autumn (Wilderbuer et al. 1992). Yellowfin sole are managed as a single stock in the BSAI management area as there is presently no evidence of stock structure.

Because reliable biomass estimates do not exist for squids in the Bering Sea and Aleutian Islands (BSAI), harvest recommendations are made using Tier 6 criteria. Under Tier 6, Overfishing Level (OFL) is defined as the average catch during the period 1978-1995, and Acceptable Biological Catch (ABC) is defined as 0.75 * OFL. As a result the harvest recommendations do not change from year to year. New information regarding squids comes mainly from the eastern Bering Sea (EBS) slope and Aleutian Islands (AI) trawl surveys. Because these are biennial surveys, full assessments are only conducted in years when those surveys occur. In “off” years, an executive summary is prepared with updated catch data.

The Bering Sea and Aleutian Islands (BSAI) skate complex is managed in aggregate, with a single set of harvest specifications applied to the entire complex. However to generate the harvest recommendations the stock is divided into two units. Harvest recommendations for Alaska skate (Bathyraja parmifera), the most abundant skate species in the BSAI, are made using the results of an age structured model and Tier 3. The remaining species (“other skates”) are managed under Tier 5 due to a lack of data. The Tier 3 and Tier 5 recommendations are combined to generate recommendations for the complex as a whole.

In 2005, Bering Sea/Aleutian Islands (BSAI) rockfish were moved to a biennial assessment schedule to coincide with the frequency of trawl surveys in the Aleutian Islands (AI) and the eastern Bering Sea (EBS) slope. These surveys occur in even years, and for these years a full assessment of shortraker rockfish in the BSAI area will be conducted. The shortraker assessment is conducted with Tier 5 methods. In 2012, a surplus production model was applied to a time series of survey biomass estimates to obtain the current estimated biomass. The 2012 full assessment can be found at http://www.afsc.noaa.gov/REFM/docs/2012/BSAIshortraker.pdf. An exploitation rate is then applied to the estimated current biomass to obtain the ABC and OFL.

The shark complex (Pacific sleeper shark, spiny dogfish, salmon shark and other/unidentified sharks) in the Bering Sea and Aleutian Islands (BSAI) is assessed on a biennial stock assessment schedule. BSAI sharks are a Tier 6 complex with the OFL based on maximum historical catch between the years 1997 – 2007 (ABC is 75% of OFL). For this off-year summary, we have updated the time series of catch through Oct 24, 2013 to reflect any changes that might have occurred in the Catch Accounting System (for the years 2003 – 2013). Any changes in historical catch did not result in new estimates of maximum historical catch during 1997 – 2007 and thus did not change the proposed ABC/OFL. For further information regarding the assessment, please refer to last year’s full stock assessment, which is available online (Tribuzio et al. 2012, http://www.afsc.noaa.gov/REFM/Docs/2012/BSAIshark.pdf). A full stock assessment document with updated survey and catch estimates will be presented in next year’s SAFE report.

In 2011, Bering Sea and BSAI sculpins were moved to a biennial assessment schedule to coincide with the frequency of trawl surveys in the Aleutian Islands (AI) and the eastern Bering Sea (EBS). These surveys occur in even years, and for these years, full assessment of sculpins in the BSAI will be conducted. The 2012 full assessment can be found at http://www.afsc.noaa.gov/REFM/Docs/2012/BSAIsculpin.pdf. The sculpin assessment is conducted with Tier 5 methods. In this assessment, the current estimated biomass is obtained from mean biomass estimates over the past four survey years for the six most abundant sculpins in the BSAI: bigmouth (Hemitripterus bolini), great (Myoxocephalus polyacanthocephalus), plain (Myoxocephalus jaok), threaded (Gymnocanthus pistilliger), warty (Myoxocephalus verrucosus), and yellow Irish lord (Hemilepidotus jordani). An exploitation rate is then applied to the estimated current biomass to obtain the ABC and OFL. The sculpin complex mortality rate is a biomass-weighted average of the instantaneous natural mortality rates for these six species. The complex mortality rate may change as new survey data become available.