Detection of marine mammal vocalizations off Cape Hatteras, modulated by the Gulf Stream

Abstract

To assess the ecological impact of extracting energy from the Gulf Stream, the University of North Carolina Coastal Studies Institute has deployed a mooring on the continental slope off Cape Hatteras at a depth of 230 m, equipped with an ADCP, a CTD, and a hydrophone. Analyzing data from the first deployment, we automatically detected marine mammal vocalizations. We found a strong correlation between the amount of vocalizations and the position of the Gulf Stream, with vocalizations increasing when the Gulf Stream was farther offshore. We then derived sound speed profiles for the region around the mooring using temperature and salinity profiles collected by WHOI Spray gliders. These sound speed profiles were fed into a propagation modeling tool. When the Gulf Stream was far offshore with respect to the mooring position, the model showed a set of rays that propagate down the slope in an acoustic channel along the bottom. When the Gulf Stream was nearly over the mooring, the range of angles that could propagate down the slope was reduced by a factor of six. Therefore, the propagation models suggest that the observed correlation is due to a propagation effect, resulting from the varying position of the Gulf Stream.