| Summary: | This project addresses the seabed contact and benthic habitat impact aspects of several trawl groundgear configurations. Recent Alaska Fisheries Science Center (AFSC) and industry cooperative work showed that raising trawl groundgear (sweeps and footrope) above the seabed via widely-spaced bobbins reduces the direct contact area of the gear, along with crab mortality and flatfish bycatch; while maintaining fishing performance for pollock. The project fieldwork will compare bottom-contact characteristics and benthic impacts of raised groundgear by systematically varying weight, spacing and seafloor clearance. We aimed to: 1) determine susceptibility of structure-forming geological and biological seabed features to these new groundgear to evaluate the potential for adverse habitat impacts; 2) quantify the component-specific (e.g. sweep, footrope) seabed contact for each groundgear configuration; and 3) compare the contact-adjusted swept areas of, and habitat-feature susceptibilities to, each configuration. The dataset includes multiple types of data: text files, excel files, photos, tilt sensor, DIDSON sonar and video. More specifically, it holds scientists' notes (text files) from the bridge and deck, CSV files containing various information (Metadata workbook, Swept area Workbook and Seafloor Clearance workbook), Globe data (GPS software, Marks and Tracks), and tilt sensor data (Hobo software). There is also underwater video, DIDSON sonar data, photos and video from on deck operations. All seafloor imagery was taken with AFSC built underwater cameras. Also included are still pictures of work operations on the deck of the vessel. The video files and photos have been stored separately and are available upon request. The DIDSON and video data were used to locate the trawl tracks and to do the sea whip condition assessments. The Globe data were used to mark our experimental footrope trawl tracks and our camera/sonar observational sled tows. The Tilt sensor data were used to examine the height off bottom of various footrope components. The CSV files consolidate the raw data in the Metadata workbook; the Swept Area file contains the cleaned data used in Swept Area models, and the Seafloor Clearance file contains the Tilt sensor data and how the sensors were calibrated. This dataset was generated under NPRB project 1319.
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