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    • AFSC/RACE/GAP/Palsson: Gulf of Alaska and Aleutian Islands Biennial Bottom Trawl Survey estimates of catch per unit effort, biomass, population at length, and associated tables

    Metadata Updated: April 1, 2024

    The GOA/AI Bottom Trawl Estimate database contains abundance estimates for the Alaska Biennial Bottom Trawl Surveys conducted in the Gulf of Alaska and the Aleutian Islands in alternate years. The estimates build upon raw and summary data available from the RACEBASE database and include calculated catch-per-unit-effort (cpue)s for principal species of groundfish and key invertebrates for each survey region. The cpues are averaged by survey strata, and then average cpues are multiplied by stratum areas which results in estimates of biomass and numerical abundance. Length and age data are combined with abundance to estimate the population at length and sex and population at age and sex.

    Access & Use Information

    License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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    Dates

    Metadata Date February 29, 2024
    Metadata Created Date October 28, 2022
    Metadata Updated Date April 1, 2024
    Reference Date(s) (publication)
    Frequency Of Update asNeeded

    Metadata Source

    Harvested from NMFS AFSC

    Other Data Resources

    Additional Metadata

    Resource Type Dataset
    Metadata Date February 29, 2024
    Metadata Created Date October 28, 2022
    Metadata Updated Date April 1, 2024
    Reference Date(s) (publication)
    Responsible Party (Point of Contact, Custodian)
    Contact Email
    Guid gov.noaa.nmfs.inport:22956
    Access Constraints Cite As: Alaska Fisheries Science Center, [Date of Access]: AFSC/RACE/GAP/Palsson: Gulf of Alaska and Aleutian Islands Biennial Bottom Trawl Survey estimates of catch per unit effort, biomass, population at length, and associated tables [Data Date Range], https://www.fisheries.noaa.gov/inport/item/22956., Access Constraints: "FISMA Controls are in place to protect stored data from unauthorized access and/or disclosure"
    Coupled Resource
    Frequency Of Update asNeeded
    Harvest Object Id 2c042080-cd2d-461f-a5d1-db5a80c5f945
    Harvest Source Id 26a29bb9-50b0-47fd-920b-edc74aa6ec76
    Harvest Source Title NMFS AFSC
    Licence NOAA provides no warranty, nor accepts any liability occurring from any incomplete, incorrect, or misleading data, or from any incorrect, incomplete, or misleading use of the data. It is the responsibility of the user to determine whether or not the data is suitable for the intended purpose.
    Lineage NOAA’s Alaska Fisheries Science Center conducts the Alaska Biennial Bottom Trawl Survey of the Gulf of Alaska (GOA) and Aleutian Islands (AI) in alternate years. These surveys have been conducted since 1980 in the AI and since 1984 in the GOA and conform to NOAA Protocols for Groundfish Bottom Trawl Surveys of the Nation’s Fishery Resources (2004, G. Stauffer compiler, NOAA Technical Memorandum NMFS-SPO-65). The survey consists of three chartered commercial fishing vessels that tow a bottom trawl at randomly-selected stations stratified by region, depth, and in the case of the GOA, habitat. For the GOA survey, the sampling frame is known trawlable or new sites throughout the survey area, stratified by management areas; by shelf, slope, or gully habitats; and by depth zones including 0-100 m, 101-200 m, 201-300 m, 301-500 m, 501-700 m, and 701-1000 m (for GOA survey methodology, see von Szalay et al. 2010 Data Report: 2009 Gulf of Alaska Bottom Trawl Survey, NOAA Technical Memorandum NMFS-AFSC-208). For the AI survey, the sampling frame is past successfully towed stations, stratified by management region and the same GOA depth zones but only as deep as 500 m (for GOA survey methodology, see von Szalay et al. 2011. Data Report : 2010 Aleutian Islands Bottom Trawl Survey. NOAA Technical Memorandum NMFS-AFSC-215). At each station the research trawl is set for a targeted period of 15 min and if the tow is successful, the catch is processed. Catch processing includes identifying, counting, and weighing all living taxa, collecting length measurement for commercially and ecologically important groundfish and invertebrate species, and collecting other materials, such as age structure, for laboratory or other scientific analysis. For each tow, detailed data are collected about the characteristics of the sample including position, time, depth, surface and bottom temperatures, and net characteristics. Sensors on the net measure how the net is fishing, and we track the contact of the foot rope with the seafloor, the width of the net at the wing tips, and the height of the headrope. Tow-by-tow data are entered into computer databases or acquired electronically. Once the survey is completed, the data are error checked and finalized into a database known as RACEBASE. These data are further processed into estimates of abundance in terms of biomass and numbers of organisms. Estimates of abundance are based upon the area-swept technique whereby the catch per unit of effort (cpue) is computed for each successful station as the weight or count of each species divided by the area that the net contacted the seafloor during the tow. These calculated cpues are then averaged among the stations in each stratum and then multiplied by the calculated area of the stratum (as measured from digitized nautical charts and a geographic information system). The product of these terms is an estimate of the biomass or numerical abundance (see von Szalay et al. 2010 Data Report: 2009 Gulf of Alaska Bottom Trawl Survey, NOAA Technical Memorandum NMFS-AFSC-208 and von Szalay et al. 2011. Data Report : 2010 Aleutian Islands Bottom Trawl Survey. NOAA Technical Memorandum NMFS-AFSC-215 for more complete methods). The abundance estimates for the strata are combined by area-depth categories for convenient analysis. In addition, the population-at-length is estimate by applying length-sex frequency observations to the population abundance estimates. As age structures are evaluated for age determination, the population-at-size estimates are used with an age-length key to estimate the population-at-age structure of selected species.
    Metadata Language eng
    Metadata Type geospatial
    Progress underDevelopment
    Spatial Data Service Type
    Spatial Reference System
    Spatial Harvester True
    Temporal Extent Begin 1980

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