| dc.description.abstract | Some wide-ranging elasmobranch species are frequently reported to occur at topographic highs, which are topographic prominences that rise from the sea floor and provide significant positive and structural relief in an otherwise level landscape. Examples of places where some sharks and rays appear to concentrate include Saint Paul's Rocks, the Bahamas, the Cocos Islands, Galapagos Islands, Hawaiian Islands, Aldabra Atoll, Johnston Atoll, and the Marshall Islands. In the northwestern Gulf of Mexico, an array of topographic highs comprising submerged hard-banks and reefs, and offshore petroleum platforms are notable. Among these features are the Flower Garden Banks, the northernmost coral reef communities on the North American continental shelf, where divers have reported several species of elasmobranchs aggregating. This paper reports on the biological and ecological diversity of elasmobranchs occurring at several topographic highs in the northwestern Gulf of Mexico, including the Flower Garden Banks; describes the seasonal habitat use, social organization and behavior of elasmobranchs at the sites surveyed; and evaluates topographic highs as habitat for some elasmobranch species. Species found utilizing the topographic highs surveyed include the nurse shark (Ginglymostoma cirratum), whale shark (Rhincodon typus), tiger shark (Galeocerdo cuvier), silky shark (Carcharhinus falciformis), dusky shark (C. obscurus), Caribbean reef shark (C. perezi), sandbar shark (C. plumbeus), scalloped hammerhead shark (Sphyrna lewini), southern stingray (Dasyatis americana), roughtail stingray (D. centroura), spotted eagle ray (Aetobatus narinari), lesser devil ray (Mobula hypostoma), sicklefin devil ray (M. tarapacana), and manta ray (Manta birostris). Occurrence data indicate these species form three temporal assemblages: the winter pelagics, summer pelagics, and resident assemblages. Data also show that dissimilar topographic highs (mid-shelf, shelf-edge, and artificial shelf-edge) function as seasonal feeding, nursery, or mating habitat for different life stages and species. A model and postulate simplifying elasmobranch-topographic high habitat associations are presented from which future research and conservation plans may be organized. | en |
