The U.S. Geological Survey (USGS), in cooperation with the National Oceanographic and Atmospheric Administrationâ€™s (NOAA) National Marine Fisheries Service (NMFS), and Florida State University (FSU), collected the data presented here as part of a larger study of seafloor habitats on the shelf edge of the northeastern Gulf of Mexico. It is a pilot study, carried out to demonstrate the utility of geologic mapping to fisheries management issues. This report contains sidescan-sonar mosaics, seismic-reflection profiles, texture and calcium carbonate content of sediment samples and interpretative maps of the seafloor morphology, sediments, and benthic habitats of the study area.
The study area is an approximately 150-km2 area along the shelf edge in the northeastern Gulf of Mexico. The site is on the eastern side of the DeSoto Canyon and 75 km due south of Cape San Blas on the Florida panhandle. Water depth ranges from about 50 meters (m) to 120 m. It was chosen because reports from fishermen suggested that high-relief rocky outcrops, which are preferred by gag grouper as spawning aggregation sites, would be abundant. The geologic maps help the fisheries biologists select station locations for ongoing monitoring studies and provide a basis for siting of future reserves.
In 1997, four surficial sediment grab samples were collected by C. Koenig during a cruise of the NOAA R/V Chapman. In 1998, an additional 51 sediment grab samples were collected by C. Gledhill during a cruise of the R/V Chapman and 3 by G. Fitzhugh during a cruise of the R/V Carretta. All samples were collected using a van Veen grab sampler. All samples (except those that were made up of chunks of coral or coral rubble) were analyzed for particle size and carbonate content in the sedimentology laboratory of the U.S.G.S. at Woods Hole, Massachusetts. Texture terminology used in this report is according to Folk (1974). The percent of calcium carbonate material was determined by weight loss of 15 grams of bulk material after digestion with 10 percent hydrochloric acid. Details of the laboratory techniques can be found in Appendix I: Sediment Texture Analysis Techniques. The data are presented in Appendix II: Table of Sediment Analyses.