Humpback whales use “bubble nets” to catch krill, which researchers have determined to be an example of tool modification and understanding.
That’s following a new Royal Society Open Science article on the whales that included University of Hawaiʻi researchers.
Groups of whales have been known to use bubbles to catch krill, but some solitary whales in Alaska have also been observed making complex bubble nets.
The whales create layers of bubble rings to form the net. They can control the number of bubble rings and adjust the size and depth of the net to catch the shrimp-like krill.
They can catch up to seven times more krill per feeding through the unique hunting technique.
“Other species have been shown to use bubbles or blow bubbles in different ways. … But this is really the only species that forms these complete multi-ring nets to, what we think is, concentrate their prey,” said William Gough, a researcher with UH’s Hawaiʻi Institute of Marine Biology’s Marine Mammal Research Program.
The use of bubble nets is relatively rare, Gough said. When groups hunt for herring, they use “bubble curtains” that generally require a continuous stream of bubbles, instead of “pusles” of bubbles used in bubble nets.
That’s in part because they need the continuous stream to catch the herring, which are better at escaping the bubbles than krill.
“You really need that continuous stream of bubbles to keep them corralled in. Essentially, these animals are sort of manipulating the structure of these nets based on what they're trying to capture,” Gough said.
Co-author of the study and MMRP Director Lars Bejder said, in a statement, “This impressive behavior places humpback whales among the rare group of animals that both make and use their own tools for hunting.”
Because using bubble nets isn't common, Gough said, it’s difficult to make broad assumptions about why humpback whales use them.
They have been used for cooperative hunting in Antarctica, while solitary humpback whales have been seen forming bubble nets in Alaska.
Gough said the Alaska whales are part of the same population that spends winters in Hawaiʻi.
