By Stephen Beech
Whales enjoy long-distance relationships – synchronizing their dives with pals 60 miles away, suggests new research.
Scientists who analyzed the seemingly random movement of bowhead whales in the Arctic Ocean uncovered a 24-hour diving cycle and synchronization with others over long distances.
Bowhead whales are among the largest and longest-living mammals in the world.
Scientists say they play a vital role in the marine ecosystems of the Arctic Ocean, but relatively little was known about their foraging and diving habits.
Now, a team of researchers from Japan, Greenland and Denmark have detected patterns in the whales’ behavior that could offer clues into how they forage and socialize.
The team studied 144 days of diving records of 12 bowhead whales tagged in Disko Bay, West Greenland.
Because whale diving behavior can be seen as a “chaotic, self-sustained oscillation” that balances the need for food at depths with the need for oxygen at the surface, the researchers used a dynamical systems chaos approach to uncover patterns within the apparently disorderly collective behavior.
Their analysis, published in the journal Physical Review Research, detected a 24-hour cycle of diving during the Spring, with the whales swimming deepest in the afternoon to track the daily movement of their prey towards the surface, a phenomenon known as the “diel vertical migration”.
Professor Mads Peter Heide-Jørgensen, of the Greenland Institute of Natural Resources, said: “We found that foraging whales dive deeper during the daytime in Spring, with this diving behavior being in apparent synchrony with their vertically migrating prey.
“Until now, this hasn’t been shown for Spring, and remained contradictory for autumn.”
The research team also made the surprising discovery of two bowhead whales diving “in synchrony” over the course of a week at a time, even when they were around 100 kilometers apart.
The pair – one female and one of unknown sex — were sometimes as close as 5kms and sometimes hundreds of km apart, yet they would closely time their diving bouts for durations of up to a week, although to different depths.
The synchronization was observed when they were within acoustic range of each other, which can exceed 100 kilometers (60 miles), although the researchers didn’t record the whales’ sounds to determine whether they were interacting, as it remains a technically challenging task.
Research team member Professor Jonas Teilmann, of Aarhus University, Denmark, said: “Without direct observations, such as recordings of the two whales, it isn’t possible to determine that the individuals were exchanging calls.”
But he added: “The observed subsurface behavior might be the first evidence supporting the acoustic herd theory of long-range signaling in baleen whales proposed by Payne and Webb back in 1971.”
Professor Evgeny Podolskiy, of Hokkaido University in Japan, said: “The possibility of acoustically connected whales, which seem to be diving alone but are actually together, is mind-bending.”
He added: “Our study identifies a framework for studying the sociality and behavior of such chaotically moving, unrestrained marine animals, and we encourage the research community to collect more simultaneous tag data to confirm if our interpretation is appropriate.”
