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  • Whistle structure and geographical variations in three delphinid species recorded in eastern Algarve Coast
    Publication . Gil, Susana; Jesus, Sérgio Manuel Machado; Soares, Cristiano
    This study aims to characterize and compare the whistle repertoires of three odontocete species, Delphinus delphis (short-beaked common dolphin), Tursiops truncatus (common bottlenose dolphin), and Pseudorca crassidens (false killer whale), in the coast of Faro. This knowledge is essential for their monitoring and conservation, particularly for this region. Especially because this is an area with high anthropogenic pressure and limited prior research. These species were chosen due to their presence in the region and high vocal activity, with special emphasis on the poorly studied false killer whale (Pseudorca crassidens), recently observed using the area as a seasonal feeding ground. Recordings were obtained between April 2022 and June 2024 using an opportunistic platform during dolphin and whale watching surveys. A total of 36 acoustic events were analyzed. Visual analysis and manual whistle extraction of ten acoustic parameters were conducted using Raven Pro: beginning, end, minimum, and maximum frequency, frequency range, duration, initial and final slope, number of inflection points, and number of steps. In total 327 whistles were analyzed and used in this study. Whistle contours were also categorized into six standard types according to previous studies (Constant, Upsweep, Downsweep, Convex, Concave and Sine). Statistical analyses were conducted to describe and categorize the repertoire of the three species. A non-parametric Kruskal-Wallis’ test was used to determine overall differences in whistles parameters among species, pairwise with Dunn’s test and adjusted with sequential Bonferroni. A non-metric multidimensional scaling (NMDS) was used to visualize acoustic separation between species. The whistles contours were also compared using a correlation matrix. Additionally, a Random Forest model measured the classification performance and the importance of each acoustic variable. Results showed significant acoustic differences in whistle parameters between species, especially between Pseudorca crassidens and the two other dolphin species. Delphinus delphis and Tursiops truncatus showed higher variability in frequency and contour type, potentially related to behavioral context or social structure. To explore potential geographic variation, Faro data was compared with published values from other geographic regions to evaluate possible geographic divergence using mean values of frequency parameters available in literature. Geographic comparisons revealed that the population of Faro exhibits distinct whistle characteristics when compared to populations from other regions. The results also showed that geographic distance alone does not predict acoustic similarity or divergence. Instead, environmental context plays a key role in shaping dolphin’s repertoire, likely driving specific acoustic adaptations. These findings contribute to baseline knowledge of local cetacean acoustic repertoires and highlight the importance of passive acoustic monitoring for population, behavioral, and conservation studies. This work reinforces the importance of regional characterization to detect alterations related to human activity and environmental change, and it supports future efforts to implement effective mitigation and management strategies for cetacean conservation in southern Portugal.
    2025-10-16Dissertação de mestrado Acesso aberto Ver mais