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Benthic Habitat Mapping
Fisheries Management on the Scotian ShelfBenthic habitat mapping was conducted on Browns Bank, southwestern Scotian Shelf, for use in Canadian fisheries management. This project took an interdisciplinary approach to mapping by integrating multibeam bathymetry, geological information (for example, sediment size and type), and benthic infauna analyses. Data were obtained from multibeam sensors, side-scan sonar, sediment grab samples, and seafloor photography. In the first stage of data analysis, high-resolution multibeam data were used to create bathymetric maps of the seafloor. The multibeam sonar also collected backscatter data. Variations in backscatter strength represent variations in sediment composition; however, backscatter intensity also can be influenced by environmental conditions (such as currents, sea state, and organisms), and is subject to calibration error. Thus, side-scan sonar was used to investigate further seafloor types and features identified from the multibeam data. In addition, sediment grabs were collected along the sonar paths. Sites for sediment grabs were chosen to provide coverage of broad areas sharing similar geological characteristics based on the multibeam and side-scan sonar data. Sediment grabs also provided three-dimensional (up to 0.5 meters sediment depth) verification of geological parameters. These data were combined to create an integrated sediment map of Browns Bank. Four major sediment types were identified: thick sand, sand over gravel lag, gravel lag with thin sand, and gravel lag.
Grab samples and underwater photographs were also used to identify benthic fauna to the lowest possible taxonomic level. Cluster analysis was used to determine associations between taxa; and analysis of variance tests confirmed relationships between species diversity and sediment type. Based on these statistical analyses along with the seafloor sediment map described above, six habitats were defined and mapped: shallow water sand, deep water sand, gravel with soft corals and sea cucumbers, gravel with scallops, gravel with brachiopods, and gravel with deposit-feeders. Ultimately, five factors, measured with a combination of benthic mapping techniques, contributed to habitat delineation: substrate type, taxonomic assemblage, habitat complexity (for example, combination of grain sizes and topography), relative current strength (low, moderate, high), and depth. This study illustrates the effective use and integration of acoustic, physical sampling, and photographic data for benthic habitat mapping. This work also demonstrates the potential for using multibeam sonar data to predict trends in benthic biological diversity, distribution, and abundance. In future, this predictive capability may be very useful for achieving fisheries management goals. Reference Kostylev, V.E., B.J. Todd, G.B.J. Fader, R.C. Courtney, G.D.M. Cameron, and R.A. Pickrill. 2001. "Benthic Habitat Mapping on the Scotian Shelf Based on Multibeam Bathymetry, Surficial Geology, and Sea Floor Photographs." Marine Ecology Progress Series. Volume 219. Pages 121 to 137.
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