Two Arctic bowhead whales synchronize their dives, demonstrating extremely long-distance acoustic communication.
Every January to May, baleen whales flock to Qeqertarsuaq Tunua, a large bay on Greenland’s west coast, to feast on plankton. In 2010, two bowhead whales (Balaena mysticetus) belongs to a group of baleen whales that enter the bay to feed. When they were about 96 kilometers apart, something extraordinary happened: They began to synchronize their dives.
In a new study published in the journal Physical Review Researchthe authors believe that even though this pair of whales cannot see each other, they can still hear each other’s sounds. This observation provides potential evidence for a 53-year-old hypothesis, Smithsonian reported on October 5.
Baleen whales are often thought to be solitary. However, some scientists believe that they move in dispersed flocks, communicating over distances of hundreds of kilometers. Biologist Roger Payne and oceanographer Douglas Webb first proposed the idea of the acoustic swarm hypothesis in 1971.
According to Evgeny Podolskiy, an environmental scientist at Hokkaido University, Japan, lead author of the new study, the diving behavior of bowhead whales at first glance seems quite chaotic and unpredictable. They make hour-long dives then stop for unknown reasons.
Podolskiy and his colleagues wanted to find order from these seemingly random things. Using satellite tracking tags, the team collected data on dive depth and location from 12 Arctic bowhead whales over 144 days. They then applied complex algorithms based on chaos theory. During the calculation, patterns begin to appear.
First, the team found that whale dives tend to follow a 24-hour cycle, being shallower in the morning and deeper in the afternoon. This is consistent with the phenomenon of Daily Vertical Migration (DVM) – the journey from the ocean surface to the deep sea and back by plankton and other small organisms. They also found that whales make their deepest dives in spring, when DVM is most intense in the Arctic.
What surprised Podolskiy, however, was the second pattern: Synchronized dives of pairs of bowhead whales in Qeqertarsuaq Tunua Bay. The research team is unclear about their relationship, but they synchronized their dives for 7 days, while staying within 96 km of each other. According to the team’s calculations, that is the maximum acoustic range for whales in the area. “This is extremely strange underwater behavior. It’s very interesting,” Podolskiy said.
Podolskiy also added that it is possible that this synchronization is just a coincidence. It’s possible that ocean conditions prompted the whales to dive simultaneously in different locations. However, synchronized diving occurs continuously for many days, so that possibility is statistically very unlikely. “We now believe it has to do with communication,” he said.