| Summary: | This project added more detail to our previously published smooth sheet bathymetry of the Aleutian Islands from 2013 so that we could improve the quality of our National Marine Fisheries Service (NMFS) bottom trawl survey bathymetry-based strata, improve our NMFS bottom trawl survey relative biomass estimates, and improve our stock assessments. Smooth sheets are the original, highly detailed precursors to the navigational charts, and we have developed the methods of working with them to publish the most detailed and accurate bathymetry for several regions of Alaska. NPRB Project 1604 provided funding for 1.5 years of the continued work of a highly trained and experienced GIS technician to revise our 2013 Aleutians smooth sheet bathymetry by accomplishing several specific objectives. 1) We digitized the shoreline of 3,009 islands for a total of 3,272 segments with a total length of 8,228,814 meters, all annotated with the MHW (Mean High Water) value from the smooth sheets (Shoreline.zip). 2) We proofed, edited and digitized 187,177 cartographic features including depths or elevations whenever they were available (Features.zip). We incorporated available 3) multibeam and 4) single-beam data into a new 5) 100 m horizontal resolution final depth surface (ai_grid_100m.zip), improving our description of deeper, offshore seafloor features and decreasing the previous gap of coverage around northern Atka Island, Amlia Island, and Seguam Island. 6) From this new depth surface we created new NMFS bottom trawl survey strata and used them to recalculate new biomass and variance estimates. In general, biomass changes were small but strata shifted spatially, as a result of more accurate depth contours (please see final report for details). 7) We calculated the size, maximum depth, maximum through depth, length, and tortuosity for the limiting passes (AI_Passes.zip). These passes serve as small connections between the North Pacific and Bering Sea. Inventory: ai_grid_100m,zip AI_Passes.zip Features.zip Shoreline.zip
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