While the “smart” animal club has been steadily adding new members, the world’s whales can be considered among the founders. The roughly 50 million-year-old animal lineage shows evidence of their own culture, can take down yachts, hunt predators in groups, and may even have their own alphabet. Now, a new study of humpback whales (Megaptera novaeangliae) in Alaska observed the animals manipulating the “bubble-nets” that they blow underwater to stun and capture prey, in order to maximize how much food they catch. Scientists believe these “bubble-nets” should count as tools wielded by the whales. The findings are detailed in a study published August 21 in the journal Royal Society Open Science.
“What I find exciting is that humpbacks have come up with complex tools allowing them to exploit prey aggregations that otherwise would be unavailable to them,” Andy Szabo, a study co-author and Executive Director of the Alaska Whale Foundation, said in a statement. “It is this behavioral flexibility and ingenuity that I hope will serve these whales well as our oceans continue to change.”
[Related: Humpback whales are organizing in huge numbers, and no one knows why.]
What are bubble-nets?
Bubble-net feeding is a hunting strategy that is used by both groups of whales and single whales. When done in a group, it is a very synchronized set of behaviors that requires communication and cooperation, which is even more evidence of their high social intelligence.
The group of whales or a single whale dives down deep below a school of fish or a small crustaceans called krill. They blow bubble rings from their blowholes to stun the organism and trap them closer to the surface. Once closer to the surface, the whales open their mouths wide and swallow everything in the bubble net before shutting their mouths. The baleen plates push out the water, while the whales swallow the animals whole.
“Many animals use tools to help them find food, but very few actually create or modify these tools themselves,” Lars Bejder, a study co-author and the director of the University of Hawai’i at Manoa’s Marine Mammal Research Program, said in a statement.
The new study looked at a population of humpback whales in southeast (SE) Alaska that eventually migrates to Hawaiʻi to mate during the winter. Their energy budget for the whole year depends on capturing and eating enough food during the summer and fall in SE Alaska. Understanding how their carefully honed hunting technique sheds some new light on how these migratory whales get enough calories to swim roughly 3,000 miles in the Pacific Ocean.
Drones and suction cups
Since they spend the vast majority of their lives under water, marine mammals are fairly difficult to study. Advances in technology have made it a little easier for biologists to get an inside look at their lives.
In this study, the team used specialty tags and drones to study the whalesʻ movements from above and below the water.
“We deployed non-invasive suction-cup tags on whales and flew drones over solitary bubble-netting humpback whales in SE Alaska, collecting data on their underwater movements,” study co-author and University of Hawaii at Manoa’s marine mammal researcher William Gough said in a statement.
However, even with these tools, it still takes practice to study whales and other cetaceans. “Whales are a difficult group to study, requiring skill and precision to successfully tag and/or drone them,” said Gough.
The tagging and footage revealed that solitary humpback whales in SE Alaska make complex bubble nets to catch krill. They not only blow bubbles in the patterns that form nets with internal bubble rings, but can control detailed aspects of the nets.
“[The whales] are actively controlling details like the number of rings, the size and depth of the net, and the spacing between bubbles,” said Bejder. “This method lets them capture up to seven times more prey in a single feeding dive without using extra energy. This impressive behavior places humpback whales among the rare group of animals that both make and use their own tools for hunting.”
Survival mechanisms
Cetaceans around the world are facing serious threats from climate change to habitat degradation to exposure to chemical and noise pollution. About 25 percent of the 92 known cetacean species are at risk of extinction. Understanding how these animals are is key to creating better policies to monitor and conserve the feeding grounds that are critical to their survival.
“This little-studied foraging behavior is wholly unique to humpback whales,” said Gough. “It’s so incredible to see these animals in their natural habitat, performing behaviors that only a few people ever get to see. And it’s rewarding to be able to come back to the lab, dive into the data, and learn about what they’re doing underwater once they disappear from view.”
[Related: A group of humpback whales is choosing violence.]
According to the team, the “rich dataset” they collected for this study will allow them to learn more about the physics and energetics behind bubble-netting.
“There is also data coming in from humpback whales performing other feeding behaviors, such as cooperative bubble-netting, surface feeding, and deep lunge feeding, allowing for further exploration of this population’s energetic landscape and fitness,” said Bejder.