Whistling up help for endangered dolphins
● The whistles bottlenose dolphins use to communicate underwater are unique to each dolphin, and scientists have now made a breakthrough by using those whistles to map how big the dolphins populations are and where they travel.
The breakthrough in bottlenose dolphin research could make a crucial difference to humpback dolphins, which are facing extinction.
Until now, estimates have relied on photographs, but the co-directors of the science institute Sea Search, Tess Gridley and Simon Elwen, said their use of hydrophones will change that.
“When bottlenose dolphins are born, they develop a signature whistle in the first months of life,” said Gridley, a senior researcher, in a paper about the findings just published in the Journal of Mammalogy.
“They listen to the environment they’re in and develop their own whistle. This means each one basically has a ‘label’ — it’s like a name.”
These whistles are “friendly sounds” that help the animals stay in contact, communicate and find their way back to one another if they get separated.
By recording these signature whistles over time and in different places, the researchers could map the movements of the dolphins and calculate how many there are in a populatioPn.R
Gridley and Elwen run Sea Search from Muizenberg, Cape Town, but they also lead the Namibian Dolphin Project in Walvis Bay and are affiliated with Stellenbosch University and the University of Cape Town.
Over the past 12 years, the Namibian project has been researching bottlenose dolphins and the result is a catalogue of more than 55 signature whistles.
“Across all species of animals there are different sounds they make and there is recognition between mother and child, but with dolphins each having a signature whistle, that is the next level up in terms of complexity and that is why they are so interesting,” said Gridley.
“Our research could be applied for other types of dolphins. The humpback dolphins are endangered, with only around 500 left. Acoustic monitoring can provide information on their numbers, how far they range, and other information.”
This will be helpful with the humpbacks because, said Gridley, “they are horrible to work with”.
“They hang out really close to the breakers and they are shy and elusive.
“So being able to put a hydrophone in the water 24 hours a day means you will capture far more information than on a normal boat survey.”
Research for the paper was initiated by marine biologist Emma Longden, who interned at the Namibian Dolphin Project for a month in 2016 while she was studying at the University of Plymouth in the UK.
In 2018 she returned to complete her work on the project, and in total she analysed more than 4,000 hours of acoustic data from four hydrophones positioned along the coast south and north of Walvis Bay.
“One of the great things about bioacoustics is that you can leave a hydrophone in the water for weeks at a time and collect so much data without interfering with the lives of the animals you are studying,” Longden said.
Gridley said her passion for bioacoustics stretches far beyond the dolphins, and she is currently engaged in research on Egyptian geese.
The technology “can even be used for gunshot monitoring” in reserves to curb poaching, and can also be employed to “pick up on illegal deforestation”.
Other applications include detecting illegal fishing activity at sea.