Figure 1 – Bottlenose dolphins (Tursiops truncatus) following a trawler.
“Noise pollution” in the marine environment has been an increasing concern for conservationists and marine researchers in the past decades. Underwater sounds caused by ships have no impact on humans, however, they may have severe effects on marine life, especially marine mammals.
Engine noise from boats increases with size, power, load and speed. It overlaps with the frequency range of many cetaceans.
There are many different types of sounds emitted by dolphins and in this project, we focused on the acoustic signal of whistles. They are narrowband tonal calls with durations up to a few seconds and fundamental frequencies that typically fall between 5 and 20 kHz. They are thought to be a method of communication through water for long distances.
The purpose of this project is to classify dolphin whistles and to understand if their parameters change in presence of boats. For every whistle recorded we analyze the following parameters: shape, start and end time, minimum and maximum frequency, delta time, mean frequency, peak power, peak frequency, centre frequency, steps, harmonics, inflections.
Figure 2 – Common dolphin (Delphinus delphis) parameters table. We also collect whistles from Striped dolphin (Stenella coeruleoalba) and Bottlenose dolphin (Tursiops truncatus).
During every sighting, we also collected data of boat presence and measured the level of ambient noise (peak amplitude and equivalent continuous sound level).
Figure 3 – Spectrogram of Striped dolphin whistles.
Dolphins can change their vocalizations when the level of ambient noise is high. This variation allows them to transmit their signals and avoid masking. The Bioacoustics Team will compare the whistles parameters with the presence and noise of boats in order to understand if this type of anthropogenic impact could affect the communication system and the social interactions of dolphins in the Aegean Sea.
Simone Antichi
BSc Marine Biology, Universita Politecnica delle, Italy
and Dahlia Hassell,
BSc Aquaculture and Marine Resources Management, Wageningen University and Research, The Netherlands
