New research from the University of Hawaiʻi at Mānoa focuses on discovering a behavior that is critical to humpback whale survival and building a case for counting humpback whales among the rare animals that make and use their own tools.
Every winter, thousands of humpback whales migrate to the Hawaiian Islands to mate, give birth and raise their young.
Researchers at the Hawaii Institute of Marine Biology knew that humpback whales build “bubble nets” for hunting, but they discovered that they manipulate these bubble nets to maximize their food intake in Alaska’s feeding grounds.
The research, conducted in collaboration with the Alaska Whale Foundation, was published in Royal Society Open Science.
“Many animals use tools to find food, but very few make or modify these tools themselves,” said Lars Bejder, co-leader of the study and director of the Marine Mammal Research Program. “We found that solitary humpback whales in southeast Alaska make complex bubble nets to catch krill, tiny shrimp-like creatures.
“These whales skillfully blow bubbles in patterns that form nets with internal rings, actively controlling details such as the number of rings, the size and depth of the net, and the spacing between bubbles,” Bejder continued. “This method allows them to catch up to seven times more prey in a single dive without expending additional energy.”
Hunting success is critical to whale survival. Humpback whales’ year-round energy budget depends on their ability to catch enough food in Alaska during the summer and fall. Deciphering the nuances of their carefully refined hunting technique sheds light on how migratory humpback whales burn enough calories to traverse the Pacific.
Marine mammals such as whales, dolphins and porpoises are difficult to study. For this study, researchers used special transmitters and drones to study the whales’ movements above and below water.
“We have attached noninvasive suction cup tags to whales and flown drones over individual humpback whales in Alaska that are catching bubble nets to collect data on their underwater movements,” said William Gough, co-author and Marine Mammal Research Program researcher. “The tools are incredibly powerful, but refining them takes practice. Whales are a difficult group to study, and it takes skill and precision to successfully tag and/or drone them.”
Whales and dolphins face a variety of threats worldwide, ranging from habitat destruction, climate change, fishing to chemical and noise pollution. A quarter of the 92 known whale species are threatened with extinction and there is a clear and urgent need to implement effective conservation strategies to protect them. Understanding this essential behavior allows resource managers to better monitor and protect the feeding grounds that are critical to their survival.
“This is a rich dataset that will allow us to learn even more about the physics and energetics of solitary bubblenet fishing,” Bejder said. “There are also data from humpback whales engaging in other feeding behaviors, such as cooperative bubblenet fishing, surface feeding, and deep lunging, allowing further exploration of the energetic landscape and fitness of this population.”
“I find it exciting that humpback whales have evolved complex tools to exploit prey concentrations that would otherwise be unavailable to them,” said Andy Szabo, executive director of the Alaska Whale Foundation and co-leader of the study. “I hope this behavioral flexibility and ingenuity will benefit these whales as our oceans continue to change.”
This work was supported by Lindblad Expeditions – National Geographic Fund, the University of Hawai’i at Mānoa, and a grant from the Department of Defense Defense University Research Instrumentation Program.
