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Abstract: A combination of autonomous acoustic recorders and visual surveys was used to determine the seasonal and spatial distribution of dolphins on the West Florida Shelf (WFS), Gulf of Mexico, USA. Acoustic detection rates were calculated using a model that adjusted the theoretical detection range for variations in ambient noise, which was found to be highly variable. Both acoustic and visual techniques indicated dolphins were present on the WFS year-round. Acoustic detections were not identified to species, but bottlenose dolphins (Tursiops truncatus), Atlantic spotted dolphins (Stenella frontalis), and a single group of rough-toothed dolphins (Steno bredanensis) were visually sighted, with the highest sighting rates for bottlenose dolphins. Both dolphin acoustic detection rates and bottle-nose dolphin visual sighting rates decreased from inshore to offshore waters, and were especially high in waters adjacent to Tampa Bay, a major estuary. Dolphin acoustic detection rates and bottlenose dolphin visual sighting rates also suggested a habitat shift from deeper to shallower water in summer and/or autumn. Atlantic spotted dolphins were rarely observed in water shallower than 20 m, and appeared to move into shallower and more northerly waters during the summer. Both spatial and temporal variations in dolphin acoustic detection and visual sighting rates can potentially be explained by the habitat preferences and seasonal movements of their prey. This study is the first investigation of dolphin distribution on the WFS using both visual and acoustic methodologies over a synoptic scale, and the combined techniques allowed for a more complete assessment of the temporal and spatial patterns of WFS dolphins.
Key Words: acoustics, distribution, bottlenose dolphin, Tursiops truncatus, Gulf of Mexico, Atlantic spotted dolphin, Stenella frontalis
Document type: Research article
Page Numbers: 167-187