MARE researcher Joana Castro is co-author of the study ‘Influence of Dolphin-Watching Tourism Vessels on the Whistle Emission Pattern of Common Dolphins and Bottlenose Dolphins’, which analyses the impact of tourist boats on the vocalisations of the Algarve's dolphins.
In recent years, the Algarve coast has seen a significant increase in the activity of dolphin watching boats, a sector that contributes considerably to the socio-economic development of the region. However, despite bringing various benefits to the local economy, trafficking can have negative impacts on biological communities and marine habitats, such as reducing biodiversity and altering animal behaviour. The underwater noise generated by boats is particularly harmful to dolphins, whose vocalisations play an essential role in communication and social interactions.
Dolphins produce a wide variety of vocal and non-vocal sounds that they use to orientate themselves, explore the environment, interact with other members of the group, hunt and detect predators. Tonal vocalisations, such as whistles, are especially important for social cohesion, as they allow dolphins to recognise each other and maintain physical and vocal contact.
In this context, a team of researchers, including MARE researcher Joana Castro, sought to understand how the noise caused by whale watching boats is affecting the vocalisations of common and bottlenose dolphins. The research, which took place between June and September 2022, revealed significant changes in the characteristics of the dolphins' whistles with the presence of boats. More specifically, the initial low and high frequencies increased, while the number of inflection points in the modulated whistles decreased. These changes may interfere with the effectiveness of communication between dolphins, jeopardising social cohesion and the survival of the population.
In addition, it was observed that the dolphins' short-term behavioural responses to underwater noise of anthropogenic origin include an increase in group cohesion, longer dives and changes in travel behaviour. Changes in breathing and behavioural patterns at the surface have also been observed, with a decrease in the time dolphins spend at the surface after approaching boats. Among the effects observed were a reduction in aerial behaviour and an interruption in feeding, social and resting activities.
The results of the study point to a potentially negative impact of increased dolphin watching tourism on the viability of local cetacean populations, which highlights the urgent need to implement effective mitigation strategies. These should include stricter regulations and greater monitoring of tourist activities, with the aim of protecting dolphin communication and behaviour in the Algarve region.
This study emphasises the importance of balancing the development of maritime tourism with the preservation of marine ecosystems, guaranteeing the sustainability of dolphin populations and the health of the marine environment off the Algarve coast.
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