SEAFLOOR CHARACTERIZATION FOR TRAWLABILITY AND FISH HABITAT USING THE SIMRAD ME70 MULTIBEAM ECHOSOUNDER IN THE GULF OF ALASKA

Jodi L. Pirtle*1, Thomas C. Weber1, Christopher D. Wilson2, Christopher N. Rooper2

1University of New Hampshire, Center for Coastal and Ocean Mapping, NOAA/UNH Joint Hydrographic Center, Jere A. Chase Engineering Laboratory, 24 Colovos Road, Durham NH 03824.

2Alaska Fisheries Science Center, National Marine Fisheries Service, National Oceanographic and Atmospheric Administration, 7600 Sand Point Way NE, Seattle WA 98115.

Rockfish (Sebastes spp.) stocks that associate with rugged seafloor types are difficult to assess due to limitations of traditional bottom-trawl sampling gear. Alternative methods that include acoustic remote sensing and video imagery may improve stock assessment in untrawlable locations. Acoustics can also be applied to identify locations where alternative assessment methods are required. We use the Simrad ME70 multibeam echosounder (ME70) and trawl survey performance data to develop a seafloor trawlability classification scheme for locations in the Gulf of Alaska (GOA).

We surveyed areas of the GOA (20-500 m depth) using the ME70 aboard the NOAA ship Oscar Dyson during summer 2011. Seafloor parameters derived from the ME70 data were used to classify seafloor trawlability including, the average backscatter measured as a function of incidence angle, scintillation index from the backscatter, and seafloor rugosity from the depth soundings. We present a preliminary seafloor trawlability classification for areas of the GOA. The next phase of this work will characterize seafloor habitats for harvested species in our survey area using ME70 data, video imagery, and species occurrence data from the trawl survey.