Overlaps of marine predators, aquaculture, and fish-aggregating devices: passive acoustics reveal site- and time-specific dolphin behavior

Aquaculture facilities and fishing procedures using floating Fish Aggregating Devices (FADs) have recently gained increasing attention due to the intensifying practice and ecosystem concerns. However, uncertainty remains regarding the conservation issues for vulnerable megafauna attracted to them. Here, we investigated the acoustic occurrence and behavior of bottlenose dolphins in the proximity of these fishing facilities in the Central Mediterranean Sea. Data were collected between February and October 2024 through autonomous recorders deployed in two fish farms and one FAD along the Maltese island’s eastern coast. Almost 300 h of recordings were analyzed to detect dolphin vocalizations. Results showed that bottlenose dolphins occurred at all sites, with temporal (both seasonal and diel) and site–specific variability, and a higher presence in the FAD proximity compared to the fish farms. Furthermore, the different acoustic behavior displayed close to the FAD compared to the fish farms suggests that the feeding strategy adopted requires higher coordination. The outcomes highlight that fish artificial floating devices, both aquaculture cages and FADs, can represent an increased opportunity for food availability but might have a differential impact on bottlenose dolphin behavior in Maltese archipelago, that should be evaluated to determine the extent of this effect on the conservation of the species for implementing appropriate sustainable management plans of the fish industry that take into account marine mammal presence.