HIGH RESOLUTION BENTHIC MAPPING USING MULTIBEAM SONAR, VIDEOGRAPHY, AND SEDIMENT SAMPLING IN THE GULF OF MAINE: APPLICATION TO GEOLOGIC AND FISHERIES RESEARCH

Jeffreys Ledge, a glacial remnant located on the inner continental shelf off New Hampshire, forms a major morphologic feature in the Gulf of Maine. In addition, Jeffreys Ledge is extremely important to Gulf of Maine fisheries. As part of a comprehensive study of the Jeffreys Ledge ecosystem, high resolution bottom mapping using multibeam sonar, videography, and bottom sediment sampling was conducted from 2002 to 2004. The mapping effort focused on an area 18.5 by 27.8 km (10 by 15 nautical miles) that included portions of Jeffreys Ledge and the surrounding basins. In addition, half the study area was located inside the Western Gulf of Maine closure area, allowing comparisons to be made between areas where ground fishing is permitted and closed areas. The multibeam survey covered 85% of the study area at a resolution of ~5m and a smaller area (2 by 3 km) at ~2m resolution. Ground truth stations were established throughout the study area with 166 videography and 149 sediment sampling stations. Bottom maps are being developed and integrated in GIS-like environments and will include classifications based on sediment grain size, sediment and morphologic types recognized in the video, and multibeam surveys. Preliminary results show the expected relationships among morphologic features, sediment types, and bottom habitats. In addition, anthropogenic effects are discernable. This presentation will discuss the sampling approach, methodologies, results, and implications to bottom mapping and fisheries management.