A Detailed Characterization of the Whistle Repertoire of Fraser's Dolphins ( <scp> <i>Lagenodelphis hosei</i> </scp> ) From the Lesser Antilles

ABSTRACT Fraser's dolphin ( Lagenodelphis hosei ) remains poorly studied due to its elusive behavior, rarity, and preference for deep offshore habitats. While dolphins use frequency‐modulated whistles for communication, detailed acoustic descriptions exist for only a few species. This study provides the first comprehensive characterization of Fraser's dolphin whistle acoustic structure and repertoire, based on recordings from eight groups (15–300 individuals) collected during boat‐based surveys at three sites in the Lesser Antilles. A total of 2999 whistles were analyzed for acoustic structure, with 1802 contours and a subsample of 728 whistles (weighted by group size) categorized using Beluga and ARTwarp to estimate repertoire size and composition. Whistles exhibited a broader frequency range (1.12–31.40 kHz) than previously reported. Acoustic overlap across sites supports the hypothesis of a proposed single population in the region. The repertoire was comprised of 298 whistle types, predominantly upsweeps and sine contours. Whistle type richness ( q = 0) did not plateau, indicating incomplete sampling of rare types, whereas Shannon ( q = 1) and Simpson ( q = 2) diversity did plateau, suggesting that the most produced whistle types were well represented in this study. These findings offer a detailed baseline of Fraser's dolphin whistle repertoire and contribute to the development of species‐specific detectors for passive acoustic monitoring, as well as future research on geographic variation, social communication, and responses to environmental and anthropogenic changes.