Humpback whales use “bubble nets” to catch krill, which researchers have found to be an example of tool modification and understanding.
This follows a new Article from Royal Society Open Science to the whales, in which researchers from the University of Hawaii also took part.
Groups of whales are known to use bubbles to catch krill, but in Alaska, some individual whales have also been observed building complex bubble nets.
The whales create multiple layers of bubble rings that make up 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.
This unique hunting technique allows them to catch up to seven times more krill per meal.
“Other species have been shown to use bubbles in other ways, or to blow bubbles. … But this is really the only species that forms these complete webs with multiple rings to, we believe, concentrate their prey,” said William Gough, a researcher with the Marine Mammal Research Program at UH’s Hawai’i Institute of Marine Biology.
The use of bubble nets is relatively rare, Gough said. When groups go hunting for herring, they use “bubble curtains,” which generally require a continuous stream of bubbles rather than the pulses of bubbles used in bubble nets.
This is partly because they need the continuous current to catch the herring, which can escape the bubbles better than krill.
“You need this continuous flow of air bubbles to keep them corralled. Essentially, these animals manipulate the structure of their webs based on what they want to catch,” Gough said.
Study co-author and MMRP director Lars Bejder said in a statement: “This impressive behavior places humpback whales among the rare group of animals that make and use their own tools for hunting.”
Because the use of bubble nets is not common, it is difficult to make general assumptions about why humpback whales use them, Gough said.
They have been used for communal hunting in the Antarctic, and in Alaska individual humpback whales have been observed forming bubble nets.
Gough said the Alaska whales are part of the same population that spends the winter in Hawaii.
