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Influência do ciclo das marés no padrão de avistamento do golfinho-comum (Delphinus delphis) no estuário do Tejo
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Resumo(s)
This study analyzed the influence of the tidal cycle on the sighting pattern of common dolphins (Delphinus delphis) downstream of the Tagus estuary, as part of the “Observatório Golfinhos no Tejo” program. The methodology consisted of applying the scan sampling method, with observations made from the VTS tower in Algés between March 2023 and March 2025, totaling 1092 hours of effort over 216 days. The data collected, using binoculars and a telescope, included observed behaviors, environmental conditions, location, and human activities. To assess the influence of the type of tide on occurrences, as well as the tidal phases on occurrences, behaviors, and spatial distribution of the common dolphin, statistical tests such as chi-square and Kruskal-Wallis were applied. The results revealed that the occurrence of common dolphins is influenced by the phases and type of tide, with a higher frequency of occurrence during ebb and slack tide. Spatial distribution varied according to the tidal phases, while the type of behavior did not change significantly between phases, suggesting a stable behavioral strategy. The search for prey and feeding were more evident during low tide, suggesting an association between food availability and this phase. It was also observed that the species adjusts its presence and activity in response to the ecological opportunities provided by tidal dynamics, optimizing feeding behavior according to local estuary conditions and minimizing energy costs. Travelling and prey search were the most frequently observed behaviors (84,7% of occurrences), showing that the Tagus estuary is an important passageway and feeding area for the common dolphin.
Descrição
Relatório de estágio de mestrado, Ecologia e Gestão Ambiental, 2026, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
“Observatório Golfinhos no Tejo” scan sampling behaviors tidal phases spatial distribution