Observers have recorded 22 separate instances of humpback whales gathering in large groups. This is strange behavior in the giant aquatic mammals, who don't swim in groups of more than a few individuals.
Humpbacks aren't very social. They typically traverse the waters alone or in pairs. Scientists have observed that sometimes the whales come together in very small groups for cooperative feeding. However, these small gatherings don't last for more than a few hours before each whale goes off on its own again.
The new behavior researchers have observed is therefore puzzling. In 2011, 2014, and 2015, research crews spotted “super-groups” of whales off the coast of South Africa. They saw groups of up to 200 individuals feeding furiously in the water.
As if the numbers weren't strange enough, the whales also weren't where the research crews expected them to be. In the summer months, humpbacks travel to the Antarctic region to feed. When the researchers spotted the super-groups, it was autumn and they were further up north than where they usually found prey. Humpbacks usually travel to warmer waters north of Antarctica, where the females give birth and nurse their young.
Gísli Vikingsson, head of whale research at Iceland's Marine and Freshwater Research Institute, has been studying whales for years. He says that this behavior in humpbacks is unprecedented. He and his colleagues published their findings on their strange discovery on March 1.
For now, researchers can only guess at what is causing the humpbacks' strange new behavior. One theory is that the availability of prey may have caused the whales to come together in large groups. After all, scientists have observed cooperative feeding behavior in whales, just not in groups as large as the ones seen recently. Also, records show that a century ago, humpbacks once fed in the same area off the South African coast.
Another explanation may be the resurgence of humpback populations. Whale hunting severely reduced the humpback population to about 10%. Because the humpback whales were near-extinct, the International Whaling Commission imposed a moratorium on whale-hunting in 1966. The moratorium likely helped humpback populations to grow more and more over the past decades.
While a resurgence in population isn't surprising, Vikingsson says that humpback populations grew faster than expected. “[S]uddenly they seem to have overcome some threshold and have begun to increase very fast.” A rapid rise in numbers may have changed some of the common whale behaviors that scientists have come to expect.
Of course, there is also the possibility that this “strange” and “new” behavior may actually be old news to whales. “It’s possible that the behavior was occurring but just not where it was visible,” says Ken Findlay, lead author of the study.
The answer to this puzzling phenomenon may be one the theories above, or a combination of all of them. With humpback population numbers rising, we can expect other “strange” behaviors. Whatever is causing their super-gatherings, humpback whales are certainly proving themselves to be very intriguing.
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