Bottlenose dolphins that forage with artisanal fishermen whistle differently

Abstract

Acoustic communication is a taxonomically widespread phenomenon, crucial for social animals. We evaluate social sounds from bottlenose dolphins (Tursiops truncatus) of Laguna, southern Brazil, whose social structure is organized around a cooperative foraging tactic with artisanal fishermen. This tactic involves stereotyped and coordinated behaviour by dolphins and fishermen and is performed by a subset of the dolphin population, splitting it into two distinct social communities. We compared the acoustic parameters and type of whistles emitted by dolphins of the “non‐cooperative” and “cooperative” communities, both during their interactions with fishermen and in times where dolphins were engaged in other types of foraging. Our findings show how dolphins’ social sounds differ between foraging tactics and social communities. The frequencies of six whistle types (ascending, descending, concave, convex, multiple, flat) were significantly dependent on tactics and communities. Ascending whistles were more common than expected during foraging without fishermen, and among dolphins of the non‐cooperative community. Whistle acoustic parameters (duration, number of inclination changes and inflection points, and initial, final, maximum, minimum frequencies) also varied between social communities. In general, whistles emitted by cooperative dolphins, mainly when not interacting with fishermen, tended to be shorter, had higher frequency and more inflections than those emitted by non‐cooperative dolphins. These results suggest that different whistles may convey specific information among dolphins related to foraging, which we hypothesize promote social cohesion among members of the same social community. These differences in acoustic repertoires add a new dimension of complexity to this unique human–animal interaction.

Whistle variation in Mediterranean common bottlenose dolphin: The role of geographical, anthropogenic, social, and behavioral factors

“…Because the soundscape of a given environment may change over time, variations in dolphin whistles may be the response to varying background noise levels, for example, to facilitate signal transmission and have an effective communication (Ansmann et al, ; May‐Collado & Wartzok, ; Papale, Gamba, Perez‐Gil, Martin, & Giacoma, ). The changes in vocal behavior may also depend on factors, including group behavior and the occurrence of anthropogenic stressors (Gridley et al, ; Hawkins & Gartside, ; La Manna, Manghi, Pavan, Lo Mascolo, & Sarà, ; Marley, Salgado, & C.P., Erbe, C. and Parnum, I.M., ; Rako‐Gospić & Picciulin, ; Romeu, Cantor, Bezamat, Simões‐Lopes, & Daura‐Jorge, ). The features, such as group size and composition, are also known to influence the acoustic properties of whistles and contribute to their variation (Heiler et al, ; Quick & Janik, ).…”

Low-frequency sampling rates are effective to record bottlenose dolphins

“…Finally, T. truncatus whistles usually occur at frequencies up to 30 kHz [ 59 , 63 ]. Specifically, in the T. t. gephyreus population sampled, less than 1% of whistles had part of the fundamental frequency above 24 kHz [ 64 ]. Therefore, we can conclude that all sounds produced by T. truncatus can be recorded using a frequency of 48 kHz.…”

Boat disturbance affects the acoustic behaviour of dolphins engaged in a rare foraging cooperation with fishers

“…Both fishers and dolphins seems to benefit from this interaction via an increase in their catch (Simões‐Lopes, Fábian & Menegheti, 1998). For the dolphin population, this interaction has several implications, influencing spatial (Cantor, Simões‐Lopes & Daura‐Jorge, 2018) and social behaviour (Daura‐Jorge et al ., 2012), population parameters (Bezamat et al ., 2018) and acoustic behaviour; individuals who frequently interact with fishers whistle differently from those who tend to forage independently, suggesting a functional role of sounds in the development and execution of this foraging tactic (Romeu et al ., 2017).…”