Seafloor Characterization for Trawlability and Fish Habitat Using the Simrad ME70 Multibeam Echosounder in the Gulf of Alaska

Abstract

Groundfish that associate with rugged seafloor types are difficult to assess with bottom-trawl sampling gear. Simrad ME70 multibeam echosounder (ME70) data and video imagery were collected to characterize trawlable and untrawlable areas and to ultimately improve efforts to determine habitat-specific groundfish biomass. We surveyed areas of the Gulf of Alaska (GOA) (20-500 m depth) aboard the NOAA ship Oscar Dyson during 2011, from the Islands of Four Mountains in the Aleutians to eastern Kodiak Island. Additional ME70 data were collected opportunistically during the winter 2012 acoustic trawl surveys. ME70 data were collected continuously along the ship trackline (1-20 nmi spacing) and at fine-scale survey locations in 2011 with 100% seafloor coverage (n = 21). Video data were collected at fine-scale survey sites using a drop camera (n = 47 stations). ME70 data were matched to the spatial location of previously conducted AFSC bottom-trawl survey hauls (n = 582) and 2011 camera stations to discriminate between trawlable and untrawlable seafloor types in the region of overlap between the haul or camera path and the ME70 data. Angle-dependent backscatter strength, backscatter mosaics, and other multibeam metrics were extracted from the ME70 data at these locations. Haul locations show separation in backscatter strength based on performance, previously classified as successful or unsuccessful due to gear damage from contact with the seafloor. Successful haul locations have values that correspond to finer grainsize, or the lack of untrawlable features such as boulders and rock. A similar pattern was observed for the camera stations characterized as trawlable or untrawlable from video. The best descriptors for seafloor trawlability will be identified among multibeam metrics to map the predicted trawlability of the ME70 survey footprint. Continued opportunistic collection of ME70 data during Oscar Dyson operations will help refine existing classifications of untrawlable and trawlable areas in the GOA.

Department

Center for Coastal and Ocean Mapping

Publication Date

9-2012

Journal Title

National Habitat Assessment Workshop: Fisheries Science to Support NOAA’s Habitat Blueprint

Conference Date

Sep. 5 - Sep. 7, 2012

Publisher Place

Seattle, WA, USA

Document Type

Conference Proceeding

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