Blue whales “roll” 360 degrees to feed
THEY ARE THE LARGEST animals on the planet but when it comes to catching krill, blue whales can adeptly manoeuvre their bulky bodies to optimise an attack.
For the first time, the mammals have been observed performing full-body underwater rolls while feeding, and researchers say the behaviour has predatory benefits.
“We think that this behaviour improves the whale’s chances of engulfing the largest amount of krill possible,” says the study’s lead author Dr Jeremy Goldbogen, from the Cascadia Research Collective in the US.
Blue whale underwater behaviour recorded
During the study, which was published this week in the journal Biology Letters, Jeremy and his team attached video cameras and digital acoustic recording tags (DTAGs) to 22 whales off the coast of Southern California, in the US. The team recorded the whales’ feeding behaviour over several months.
Blue whales feed entirely on krill, consuming up to 3.6 tonnes of the tiny crustaceans each day. They gulp large mouthfuls of prey-laden water and then use their comb-like baleen as a sieve to retain the krill while forcing the seawater out.
While feeding in this way, half of the marine giants in the study performed a 360⁰ roll. “To date, this is the most impressive acrobatic manoeuvre we have measured in blue whales using these tags,” Jeremy says.
How blue whales “roll” to feed on krill
The manoeuvre consists of two distinct stages. As the whale approaches the krill, it uses its tail flukes and flippers to perform a 180⁰ roll. This positions it belly-up, with its jaw directly beneath the krill patch. The whale then opens its mouth and engulfs the krill as it completes the full 360⁰ spin.
“Krill exhibit well-known escape responses from oncoming predators – the larger the predator, the more easily the krill can detect the approach and attempt to escape,” says Jeremy. “However, if blue whales attack krill from below, they may be able to avoid being seen by the krill until it is too late.”
The technique may also help to optimise the whales’ field of view, enabling them to locate and target the densest section of a krill aggregation.
“Being able to reconstruct a whale’s behaviour under water gives us a unique insight into these enigmatic and difficult-to-study organisms,” says Jeremy.
He explains that the cameras provided insight into what the whales could see while searching for food in deep water and the DTAGs documented the whales’ sounds and movements. “The sensor within the tag allowed us to estimate the body orientation and fine-scale movement of whales while at depth,” says Jeremy.
Behaviour of oceanic mammal predators
Jeremy says this behaviour has not been seen in such a large predator before. “Although rolling behaviour has been documented in other baleen whales, the magnitude of their rolls does not typically exceed 90⁰,” he explains. “We predict that with more tag data, we will likely observe this type of behaviour in a wide variety of oceanic top predators.”
Australian marine biologist Dr Chandra Salgado Kent, from Curtin University in WA, agrees. “The use of technologies such as DTAGs gives us an insight into the behavioural ecology of these animals,” she says.
“This information is extremely difficult to capture, especially when you’re dealing with large marine animals that often occur in remote areas and spend much time under the surface of the water.”
Chandra leads an observational study of blue whales at Geographe Bay, about 200km south of Perth in WA. She says very little is known about the foraging tactics and ecology of the marine mammals and that studies like this will provide scientists with knowledge that could help conserve the species.
“Only through studies such as these can we begin to understand the animals’ capacity for fulfilling their energy requirements, which ultimately has implications on their conservation,” she says.
Video courtesy of National Geographic
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