Acoustical Behavior of Delphinid Whistles in the Presence of an Underwater Explosion Event in the Mediterranean Coastal Waters of Spain

Abstract

Underwater noise is a significant pollutant produced by anthropogenic activities carried out in the sea. Several types of acoustic sources can potentially have adverse impacts on marine fauna, especially on cetaceans. The vocalization response of cetaceans to underwater noise varies depending on noise characteristics such as duration, bandwidth, and intensity, as well as the species being insonified. Some studies report changes in vocalization properties due to continuous noise, but there is a lack of knowledge regarding impulsive noise sources, especially those related to explosive events. It is known that underwater explosions represent a serious threat to marine fauna because it produces one of the highest sound pressure levels introduced by anthropogenic activities. In this communication, an opportunistic study related to changes in the dolphin vocalizations was performed by considering two scenarios (i.e., before and after a detonation event). The acoustic raw data were recorded by a passive acoustic device installed in a mooring line deployed in the Mediterranean coast of Spain. The objective of the experimental installation was to monitor the underwater sound pressure level in the framework of the development of the Marine Strategy Framework Directive (MSFD) in Spain. A detonation event of unknown origin was recorded during the monitoring period while Delphinids were vocalizing, allowing for the observation of their acoustic reaction to the explosion. The study considers the number of vocalizations, morphology of whistles, and spectral characteristics before and after the explosion. The results obtained indicate that the number of whistles, their complexity in terms of morphology, and spectral components vary due to the explosive event, showing significant differences that will be presented and discussed in this communication.