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Percorrer por autor "Gil, Susana"

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  • Opportunistic data for assessing abundance and site fidelity of fin whales (Balaenoptera physalus) in the Faro area, Portugal
    Publication . Gennari, Ginevra; Rodrigues, Alfredo; Carvalho, Pedro; Gil, Susana; Magno, Ramiro; Castilho, Rita; Peres dos Santos, Rui Pedro
    The distribution and migration of fin whales (Balaenoptera physalus) remain poorly understood in parts of the North Atlantic. One of these regions is the Algarve in southern Portugal, which is shaped by seasonal upwelling and the exchange of Atlantic and Mediterranean waters. This area represents a potentially critical yet poorly understood habitat for this species. This study presents the first comprehensive assessment of fin whale abundance and site fidelity in the Faro area, located approximately between 36–37° N and 8–7° W. Data was collected from 2020 to 2024 through photoidentification and GPS vessel tracks, in collaboration with a local whale-watching company. A regional catalog of 86 individuals was established, and an open spatially explicit capture-recapture model estimated a population of 1.476 individuals. Sightings peaked in spring, likely linked to phytoplankton blooms and foraging opportunities. While re-sighting rates were low, some individuals returned across years, indicating possible seasonal site fidelity. Our results demonstrate the value of data collected from platforms of opportunity in an under-surveyed region, providing a foundation for ongoing monitoring efforts. Results also highlight the Faro area’s ecological relevance as a seasonal feeding ground for fin whales and offer insights to support future conservation in the eastern North Atlantic.
    2026-05-11Artigo científico Acesso aberto Ver mais
  • 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