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Percorrer por autor "Serra, Francisco Santos"

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  • Swimming behaviour in juvenile Smooth-Hammerhead Sharks (Sphyrna zygaena): Insights from UAV-Based Observations in a Coastal Nursery
    Publication . Serra, Francisco Santos; Catry, Paulo
    Apex predators such as sharks play key ecological roles, yet their populations have experienced severe global declines. Among the hammerhead sharks, the smooth hammerhead (Sphyrna zygaena) remains one of the least studied species, particularly during its early life stages. This study provides the first baseline description of the swimming behaviour of S. zygaena at a coastal nursery in Faial Island, Azores, using unmanned aerial vehicles (UAVs). Two UAV flight methods – transect and tracking flights – were employed, and tracking flights proved to be the most suitable to investigate shark behaviour. Behaviours’ durations, tail beat cycles (TBC), and swim speeds were quantified and studied under varying ecological contexts (presence of “conspecifics”, “potential prey”, and “anthropogenic” activity). A total of 37 individuals were analysed, revealing 11 distinct behaviours. “Directional” and “cruising” swimming dominated the time budget, behaviours believed to be associated with the lowest energetic costs. Overall mean TBC was 1.5 ± 0.3 s, inversely correlated with swim speed. Behavioural shifts occurred under specific contexts: activity rates increased significantly in the presence of “potential prey” and “anthropogenic” activities, with the latter’s time budget evidencing the highest proportions of “burst” and “zigzag”, the behaviours believed to be associated with the highest energetic costs. These results demonstrate that human presence may impose additional energetic expenditure on the juveniles using this coastal nursery, potentially affecting growth and survival. These findings validate UAVs as a cost-effective, non-invasive tool for fine-scale behavioural studies in shark nurseries, and underscore the importance of assessing and mitigating anthropogenic disturbances in critical nursery habitats such as that of the Azores
    2025-11-18Dissertação de mestrado Acesso aberto Ver mais