Scientists have discovered that humpback whales in south-east Alaska create and modify tools to help them hunt prey.
The tools in question are 'bubble nets', krill-catching devices used in a way that is "wholly unique to humpback whales", according to a new study published in Royal Society Open Science.
The groundbreaking research places humpbacks among a rare group of animals that manufacture and use their own tools to help them survive.
Researchers have long known that humpback whales create bubble nets to hunt. However, the new study – which focused on solitary humpback whales in south-east Alaska – reveals that the large marine mammals don't just create these nets, they also manipulate them to increase their food intake.
“Many animals use tools to help them find food,” explains Professor Lars Bejder, co-lead author of the study and Director of the Marine Mammal Research Program (MMRP) at UH Hawaiʻi Institute of Marine Biology, “but very few actually create or modify these tools themselves."
To try and find out exactly how humpback whales hunt using bubble nets, the team deployed non-invasive suction-cup tags and drones to study the whales’ movements from above and below the water.
The team observed the whales blowing bubbles in patterns, forming nets with internal rings; the number of rings, the size and depth of the net, and the spacing between bubbles were skilfully controlled by the humpbacks.
"This method lets them capture up to seven times more prey in a single feeding dive without using extra energy," says Bejder.
The hunting method is key for the survival of the whales, who rely on Alaska's rich feeding grounds to build their energy reserves before making their way to Hawaiʻi for winter, where krill is less abundant.
“It’s so incredible to see these animals in their natural habitat, performing behaviours that only a few people ever get to see," says William Gough, co-author and MMRP researcher. "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."
Gough and the team hope that understanding this unique and essential behaviour will provide resource managers with a useful information for monitoring and conserving the feeding grounds of humpback whales.
Next, the researchers plan to explore how humpback whales perform other feeding behaviours, such as cooperative bubble-netting, surface feeding, and deep lunge feeding.
This study was conducted under a NOAA permit issued to the Alaska Whale Foundation. All research was conducted under institution IACUC approvals.
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