Study of River Dolphin Reveals Extensive ‘Language’

A pair of Araguaian river dolphins. (Gabriel Melo Alves dos Santos)

(CN) – A new study released Friday of the Araguaian river dolphin, also called the Araguaian boto, suggests that further research of river dolphins could show how communication evolved in underwater mammals.

Stationed in the Araguaian River basin of central Brazil, an international team of biologists studied river dolphin interactions.

“We used underwater microphones called hydrophones and GoPro cameras to record the behavior of the animals underwater,” said University of Vermont biologist Laura May-Collado. 

The study, published Friday in the scientific journal PeerJ, explains that 20 hours’ worth of recordings captured 237 different calls, whistles and related signals from the river dolphins.

“I think the two most exciting things are that this river dolphin species appears to be more social and chatty than other river dolphin species, and that mom and calves appear to be using a special type of signal to communicate with one another,” May-Collado said.

Until this study, Araguaian boto were thought to have little to do with each other. Even spotting the creatures was difficult until the study’s leader, Gabriel Melo-Santos, of Scotland’s St. Andrews University, found a waterside fish market in Mocajuba the animals visit, looking to be fed by the people there.

Biologists knew that the Araguaian boto, which has poor eyesight, used sound to navigate and find food. The study shows how the dolphin communicates socially, using frequencies higher than long-distance communication between whales and lower than short-distance signals among marine dolphins. Now, scientists hope to research dolphins in other South American rivers, to piece together the evolution of underwater communication.

River dolphins are the “only living representative of a lineage,” May-Collado said. They diverged from other cetaceans earlier than marine dolphins, to which they are distantly related, making their communication patterns significant.

Did their sounds form to avoid echoes in a river environment, as opposed to open sea? Did their solitary ways affect their sounds? How do they compare to marine mammals with stronger group identity, such as killer whales?

“The next step is to record mothers and calves in a controlled setting so that we can learn more about the signal and how it varies among individuals,” May-Collado said.

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