Acoustic and Behavioural Strategies of Dolphins in Relation to Fishing Vessel Traffic in the Southern Gulf of Mexico

Abstract

Behavioural and acoustic plasticity allow cetaceans to exploit a variety of habitats developing strategies to overcome increasingly demanding anthropogenic pressures. Bottlenose dolphins are known to compete with artisanal fishing along the southwestern coast of the Gulf of Mexico, but the extent of marine traffic impacts on the species is unknown. We investigated dolphin behavioural dynamics through unmanned aerial vehicles (UAV) and acoustic recordings in two zones off Alvarado, Veracruz, Mexico, with high (HVP) and low-vessel presence (LVP). Within the HVP zone (at the mouth of a lagoon) known for its greater abundance of prey, dolphins focused their behavioural budget on feeding (mostly individually), with higher emission rates for echolocation trains. Conversely, at the LVP zone (located northwest and southeast of the lagoon mouth), groups were larger and their behavioural repertoire was more varied (dolphins travelled, fed, socialized and rested equally), emitting not only high emission rates for echolocation trains but also for whistles. Our findings suggest that dolphins have developed a zoning strategy through a compensatory mechanism that allows tolerance to a certain level of fishing activities and marine traffic, especially within their feeding areas, by reducing group size to individual interactions, while prioritizing certain surface and acoustic behaviour when in the presence of vessels. By using this trade-off strategy, dolphins may remain at the site and continue taking advantage of the resources, at the expense of potential long-term effects, which remain to be investigated.