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Understanding cetacean whistles is crucial for assessing their social interactions, behaviours, and responses to anthropic activities. Identifying the various types of whistles present in acoustic recordings is often challenging, but necessary for this purpose. To facilitate this process, we have developed a semi-automated deep learning approach called the “Draw Your Own Contours” (DYOC) method. This is available as an open-source software along with its associated dataset. It utilises YOLOv8m and ResNet18 to identify whistle contours. DYOC was applied to 808 minutes of audio recordings of wild, free-ranging short-beaked common dolphins from the Bay of Biscay, France. It enabled the annotation of 8,730 whistle contours, six times faster than manual annotation. These recordings were associated with observations of dolphin behaviour, the presence of fishing nets, and the activation of the DOLPHINFREE acoustic beacon. Analyses revealed that these variables affected the signal-to-noise ratio, the number of inflections, and the frequency and/or duration of recorded whistles. This study provides the first characterisation of whistle features for a population of short-beaked common dolphins in the Bay of Biscay. The annotation of whistle contours using the DYOC method helped reveal the complex acoustic behaviour of dolphins in response to external variables.

Dolphins are highly vocal cetaceans with a complex acoustic repertoire. These marine mammals rely heavily on sound for critical activities: echolocation clicks for navigation and prey detection, whistles for social communication, and pulsed sounds for less well-documented purposes. Understanding their acoustic behaviour is essential for insights into their ecology, social structure, and responses to anthropogenic noise. However, to date, there has been a lack of open-access datasets of acoustic recordings of wild free-ranging short-beaked common dolphins (Delphinus delphis) coupled with observational data. Here, we present a new dataset (https://doi.org/10.5281/zenodo.14637674, Lehnhoff, 2025a) of high-resolution acoustic recordings of (D. delphis) observed in various behavioural states, including foraging, travelling, socializing, milling, and attraction to the boat. The dataset was collected in the northern Bay of Biscay, France, in the summers of 2020 to 2022 during surveys conducted as part of the DOLPHINFREE project. Audio recordings were made during opportunistic encounters using two devices: a single high-quality hydrophone (sampling rate 512 kHz and bit depth 32 bits) and a compact array of four hydrophones (256 to 512 kHz and 16 to 24 bits) for localization purposes. The dataset comprises over 400 min of unedited audio recordings of D. delphis accompanied by visual observations. In total, we identified about 68 000 echolocation clicks, 4600 whistle contours, and more than 350 pulsed sounds. This comprehensive resource is invaluable for detailed studies of the acoustic repertoire of (D. delphis), coupled with behavioural studies or analyses of the directionality of their acoustic emissions.

By-catch is the most direct threat to marine mammals globally. Acoustic repellent devices (pingers) have been developed to reduce dolphin by-catch. However, mixed results regarding their efficiency have been reported. Here, we present a new bio-inspired acoustic beacon, emitting returning echoes from the echolocation clicks of a common dolphin ‘Delphinus delphis’ from a fishing net, to inform dolphins of its presence. Using surface visual observations and the automatic detection of echolocation clicks, buzzes, burst-pulses and whistles, we assessed wild dolphins’ behavioural responses during sequential experiments (i.e., before, during and after the beacon’s emission), with or without setting a net. When the device was activated, the mean number of echolocation clicks and whistling time of dolphins significantly increased by a factor of 2.46 and 3.38, respectively (p < 0.01). Visual surface observations showed attentive behaviours of dolphins, which kept a distance of several metres away from the emission source before calmly leaving. No differences were observed among sequences for buzzes/burst-pulses. Our results highlight that this prototype led common dolphins to echolocate more and communicate differently, and it would favour net detection. Complementary tests of the device during the fishing activities of professional fishermen should further contribute to assessment of its efficiency.

By-catch is the most direct threat to marine mammals globally. Acoustic repellent devices (pingers) have been developed to reduce dolphin by-catch. However, mixed results regarding their efficiency have been reported. Here, we present a new bio-inspired acoustic beacon, emitting returning echoes from the echolocation clicks of a common dolphin ‘Delphinus delphis’ from a fishing net, to inform dolphins of its presence. Using surface visual observations and the automatic detection of echolocation clicks, buzzes, burst-pulses and whistles, we assessed wild dolphins’ behavioural responses during sequential experiments (i.e., before, during and after the beacon’s emission), with or without setting a net. When the device was activated, the mean number of echolocation clicks and whistling time of dolphins significantly increased by a factor of 2.46 and 3.38, respectively (p < 0.01). Visual surface observations showed attentive behaviours of dolphins, which kept a distance of several metres away from the emission source before calmly leaving. No differences were observed among sequences for buzzes/burst-pulses. Our results highlight that this prototype led common dolphins to echolocate more and communicate differently, and it would favour net detection. Complementary tests of the device during the fishing activities of professional fishermen should further contribute to assessment of its efficiency.