Cetacean habitats in the northern Gulf of Mexico

Surveys were conducted in the northern Gulf of Mexico during the spring seasons of 1992, 1993, and 1994 to determine the distribution, abundance, and habitat preferences of oceanic cetaceans. The distributions of bottlenose dolphins (Tsursiops truncatus), Risso's dolphins (Grampus griseus) Kogia spp. (pygmy [kogia breviceps] and dwarf sperm whales [Kogia sima]) pantropical spotted dolphins (Stenella attenuata), and sperm whales (Physeter macrocephalus) were examined with respect to depth. depth gradient, surface temperature, surface temperature variability the depth of the 15 degreesC isotherm, surface chlorophyll concentration, and epipelagic zooplankton biomass. Bottlenose dolphins were encountered in two distinct legions: the shallow continental shelf (0-150 mi and just seaward of the shelf break (200-760 mi. Within both of these depth strata, bottlenose dolphins were sighted more frequently than expected in regions of high surface temperature variability which suggests an association with ocean fronts. Risso's dolphins were encountered over the steeper sections of the upper continental slope (200-1000 m), whereas the Kogia spp. were sighted more frequently in waters of the upper continental slope that had high zooplankton biomass. The pantropical spotted dolphin and sperm whales were similarly distributed over the lower continental slope and deep Gulf (>1000 m), but sperm whales were generally absent from anticyclonic oceanographic features (e.g. the Loop Current. warm-core eddies) characterized by deep occurrences of the 15 degreesC isotherm. Habitat partitioning, high-use areas, species accounts, environmental sampling limitations, and directions for future habitat work in the Gulf of Mexico are discussed.