Researchers have captured ground-breaking video footage of humpback whales during what is known as bubble-net feeding, that not only shows it from above, but from a whale’s point of view.
Bubble-net feeding is a complex herding technique uniquely used by humpback and Bryde’s whales, performed as a group. The whales circle their prey – usually salmon, herring, or krill – and begin to blow bubbles that corral the fish into a tight circle within the bubble "net". One whale makes the "feeding call" and they all simultaneously swim upwards with their mouths open to scoop up their dinner.
It’s one of the few surface feeding behaviors humpback whales partake in, so researchers have been able to record it before, but the whale-cams have allowed the researchers unprecedented access to how the whales are corralling their prey below the surface.
"The footage is rather groundbreaking. We're observing how these animals are manipulating their prey and preparing the prey for capture. So it is allowing us to gain new insights that we really haven't been able to do before," said Lars Bejder, director of the University of Mānoa's Marine Mammal Research Program.
"[B]asically we have two angles and the drone's perspective is showing us these bubble nets if you will and how the bubbles are starting to come to the surface and how the animals come up through the bubble net as they surface, while the cameras on the whales are telling us this from the animal's perspective, so overlaying these two data sets is quite exciting."
Curiously, this behavior is learned rather than instinctual, so not all humpback whale populations carry it out. It requires cooperation and can include up to 60 whales in one go. If you thought it was just killer whales that work together as a team to take down their prey, you’re wrong.
As humpbacks are migratory they spend half the year fattening up in the rich feeding grounds of Alaska in preparation for the 4,800-kilometer (3,000-mile) journey to Hawaii’s warm-water breeding grounds. During their time in Alaska they can feed for up to 22 hours a day, so the researchers attached suction-cup tags fitted with cameras to a group in Southeast Alaska – the only place whales are known to bubble-net feed – in a bid to try and understand this behavior better.
"In Hawai'i, it's a breeding and resting ground. When they get up to Alaska it's a foraging ground, and we're trying to understand what that whole migration pattern costs these animals and also how much prey these animals have to consume to maintain this whole migration," Bejder explains in the video above.
The data they have gleaned from the cameras and accelerometer tags (which measure acceleration forces) coupled with the drone data is revealing the details of how the whales carry out this behavior, how often they feed, and how much they must feed to gain enough weight in preparation for breeding season.
The research is part of a larger investigation into causes of possible decline in humpback whale numbers, including habitat changes, changes to food availability, and the effects of climate change.
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