Investigating the spatial distribution of a marine top predator under elevated ambient sound conditions

Summary

Many protected marine mammals use sound as a primary sensory modality for communication and foraging, so acoustic disruptions can be costly. To investigate the behavioural responses of a marine top predator, the common bottlenose dolphin ( Tursiops truncatus ), to underwater sound levels, we used a non-invasive method of localizing dolphin pods using their whistles detected on a fixed array. Additionally, for the first time, we tracked them over time, accounting for acoustic localization error using a state–space movement model. We investigated movement parameters (speed and path straightness) and the animals’ spatial distribution in relation to broadband (10–7080 Hz) and mid-frequency (2820–7080 Hz) ambient sound levels. Dolphins utilized different areas under elevated broadband and mid-frequency ambient sound levels, but the novel analysis of travel speed and directness of dolphin pod movement did not show significant variations. Bottlenose dolphins in the Mid-Atlantic Bight probably were not habituated to elevated ambient sound levels, as evidenced by their altered habitat use. Altered distributions in response to changes in the acoustic environment could impact the foraging success, health and vital rates of this protected species.