Spatial and temporal patterns of dolphin distribution and relative abundance on the West Florida Shelf based on autonomous acoustic recorder detections and visual survey data.

Abstract

Determining the abundance, movements, and distribution of animals can be accomplished using a variety of methods. Here we use boat‐based visual surveys and detection of sounds with autonomous acoustic recorders to determine the presence of dolphins in the coastal waters of the West Florida Shelf in the eastern Gulf of Mexico. The autonomous acoustic array consisted of 12 bottom‐mounted digital spectrogram (DSG) recorders deployed from June to September 2008. Whistles and echolocation trains were identified in spectrograms for each recorder. Mean active space of each recorder was determined using the Bellhop propagation model with inputs appropriate for the location, including bathymetry, frequency, bottom loss, sound velocity profiles, and weather conditions. Acoustic detections per km2 per hour were calculated for each recorder. Visual surveys spatially overlapped the acoustic array from June to August 2008. Visual detections were analyzed per unit effort in grid cells overlaying the DSG locations. The overall relative abundance of dolphin acoustic detections in recorder active spaces and visual detections in corresponding grid cells are compared. In addition, spatial and temporal patterns of the acoustic presence of dolphins are discerned from the continuous time series of acoustic recordings.