Humpback whales spend summers feeding in the cold Arctic and Antarctic waters and then migrate to tropical waters during the winters to breed and give birth. Since they don't eat at all during this time, the mammals have to ensure they have enough fat reserves to feed their calves and to sustain themselves. To optimize their prey consumption, humpback whales often create circular "nets" with bubbles exhaled from their blowholes. Now, for the first time, researchers have captured detailed footage of the so-called bubble-net fishing technique from the whale’s point of view along with, an aerial video.
“The footage is rather groundbreaking,” said Lars Bejder, study leader and director of the University of Hawaii Mānoa Marine Mammal Research Program (MMRP). “We’re observing how these animals are manipulating their prey and preparing the prey for capture. It is allowing us to gain new insights that we really haven’t been able to do before.”
With bubble-net fishing a group of whales — two or more — collaborate to enclose fish or krill inside a circle created by bubbles exhaled from their blowholes. Depending on the number of mammals participating, the bubble loop can range anywhere from three to thirty meters in diameter. Once the prey has been trapped, one of the whales will sound a feeding call. At this point, all members of the group simultaneously swim upwards to the ocean's surface with their mouths wide open to catch as many of the trapped fish as possible.
For their research, Bejder and his colleagues used suction cups to attach cameras and sensors to a few humpbacks in the cold waters of southeastern Alaska. The mammals descend upon the region annually in the summer to feed off the massive amounts of krill and other fish available, before heading south to Mexico and Hawaii to breed and give birth. The camera on the mammal's body enabled the scientists to capture the whale blowing bubbles onto the surface through the blowhole, while aerial drones seized the view of the circular bubble nets created by the whales to surround the prey.
“We have two angles, and the drone’s perspective is showing us these bubble nets if you will and how the bubbles are starting to come to the surface and how the animals come up through the bubble net as they surface, while the cameras on the whales are telling us from the animal’s perspective, so overlaying these two data sets is quite exciting,” Bejder said.
Over their three-year study, from 2016 to 2018, the scientists noticed that two humpbacks repeatedly fortified their bubble nets by splashing their flippers at the weaker parts to guide the fish directly into their mouths. The mammals sometimes even tilted one or both of their flippers, reflecting sunlight off the white skin on the underside to further disorient the already confused prey.
The observations, published in the journal Royal Society Open Science on October 16, 2019, are part of more extensive research to investigate the declining population of humpback whales in Hawaii waters. Bejder and his team believe the data gathered may help pinpoint the cause, which they suspect is the loss of prey due to climate change, and allow them to take necessary measures to resolve the issues before it's too late.
Resources: cnet.com. www.hawaii.edu,wikipedia.org