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Ref.: MsC Thesis, University of Algarve, November 2022
Abstract:
Over the last few years there has been a significant increase in the number of dolphin-watching
boats in the Algarve (Portugal), which my lead to short- and long-term impacts on the target
species (e.g., common dolphin, bottlenose dolphin). In recent decades there has been a greater
interest in the potential effects of anthropogenic noise on marine mammals, given the important
role that sound plays in the vital functions of this organisms. Several changes in the behavior
and energy expenditure of cetaceans have been documented, including impacts in the
vocalization parameters of dolphins, reduction in the communication range of whistles and
increase energy expenditure. In this study, the whistles characteristics of common dolphin
(Delphinus delphis) and bottlenose dolphin (Tursiops truncates) were analyzed in the presence
and absence of dolphin-watching tour boats to detect potential impacts in the vocalization of
dolphins. Field recordings of common dolphin and bottlenose dolphin whistles were made from
June to September 2022, using a calibrated system. Dolphin behavior and group size were
recorded, as well as the number of boats in a 300 m radius. A total of 15h of acoustic recording
was analyzed. Overall, these results showed a significant increase in start, low and high
frequency on both species when exposed to the presence of one or more dolphin-watching
observation vessels. However, when analyzing the whistles, it was possible to observe a
reduction in the number of inflection points in the presence of the same vessels. These changes
can be a dolphin strategy to avoid sound masking and increase of energy expenditure. These
findings indicate that anthropogenic impact in the form of dolphin-watching tour vessels can
influence the vocalization parameters of dolphins and such changes could have an impact if
they reduce the communication range of whistles or increase energy expenditure.
Keywords: Tursiops truncatus, Delphinus delphis, acoustic behavior, underwater noise, vocal
signals, acoustic parameters.