Humpbacks flap their flippers like underwater birds | Science News for Students

Humpbacks flap their flippers like underwater birds

Researchers spotted whales making moves once thought impossible
Aug 7, 2017 — 7:00 am EST
humpback whale

Scientists filmed this humpback whale swimming with a large group of others as it fed off the coast of South Africa. The video shows the whale using its front flippers to move toward its prey.

Charles Littnan and Ari Friedlaender

Humpbacks use their front flippers in a way researchers had thought was impossible. New video reveals these whales flap their flippers like birds flap their wings. The move propels these giants toward their fishy prey.

A humpback can measure up to 19 meters (62 feet) long. Its flippers can extend another four meters (13 feet) in front of its body. It takes a lot of force to propel that big body forward. Scientists didn't think the whales could flap their flippers fast enough to generate such force, says Paolo Segre. He’s a biologist at Stanford University in California who studies how animals move.

Segre led a team of researchers that captured video of humpbacks feeding off the coast of South Africa in November 2016. It showed the whales flapping their flippers the way birds flap their wings to move through the air (or through the water, for penguins).

Humpbacks mainly use those front flippers for steering, scientists had thought. Tails were what propelled them forward. Or so it seemed. But that guess wasn’t based on much. “Until recently, we had no idea what [the whales] were doing,” says Segre. “We just saw them when they popped up to breathe.”

video tag
This video tagging device is about the size of a pie. Once fastened to a whale with suction cups, it tracks the animal’s position, speed and acceleration. It also films the surrounding ocean, including fellow whales.
Joe Warren

That has changed with the creation of video-enhanced wildlife tagging. This technology uses sensors to measure a whale’s position, speed and acceleration. An attached video camera records the surrounding environment.

To attach a “tag," researchers must steer a small boat as close to the animal as possible. Then someone leans over the edge with a 6-meter (20-foot) pole. On the end of it swings the tag. When close enough, a researcher slings the end to slap the tag onto the whale’s back. Suction cups should hold the device in place for 10 to 12 hours.

Later, the brightly-colored device will pop off. It then floats on the water until researchers collect it. Afterward, they will download the video and details about the whale’s movements.

Humpbacks appear to be special

The video camera records what’s happening around the tagged whale. From atop humpbacks in South African waters, the cameras recorded nearby whales as they hunted for fish. And it was then that the cameras caught the unusual propulsion technique.

Adult humpbacks can weigh more than 36,000 kilograms (40 tons). Because of their size, flapping probably takes a lot of energy, says Segre. He suspects the whales only use this tactic for short sprints to get close enough to slurp up fish. 

And these whales are probably the only type that can do this, he adds. With shorter flippers, relative to their body size, other whales likely cannot generate nearly enough force to move forward by flipper flapping. The front flippers of humpbacks also are more mobile than those of any other whale. This lets humpbacks angle their flippers the right way to push them forward.

Segre and his team published their findings July 10 in Current Biology.

Flapping flippers for a burst of speed is probably a good strategy, notes Frank Fish. A biologist at West Chester University in Pennsylvania, he studies how whales move. As a humpback lowers its bottom jaw to catch prey, a throat pouch under its jaw fills like a parachute. This slows the whale.

But by using its flippers to help propel itself forward, the whale lowers the energy it will need to speed up again, says Fish.

“Think of driving a car and hitting the gas,” he says, “then hitting the brake to come to a stop and then hitting the gas again.” That repeated start-and-stop action wastes a lot of energy. Holding to a steadier speed tends to improve gas mileage. A humpback may do something similar with its flipper flapping. “By trying to maintain speed, this may reduce energy costs for the whale,” Fish suspects.

The whales’ ability to use flippers for propulsion might also help explain how some humpbacks can swim even after losing their tails in accidents, Fish says.

A humpback whale uses its front flippers to propel itself, an unusual move that researchers had never seen before.
Stanford

Power Words

(for more about Power Words, click here)

acceleration     A change in the speed or direction of some object.

angle     The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

biology     The study of living things. The scientists who study them are known as biologists.

humpback     A species of baleen whale ( Megaptera novaeangliae ), perhaps best known for its novel “songs” that travel great distances underwater. Huge animals, they can grow up to more than 15 meters (or around 50 feet) long and weigh more than 35 metric tons.

penguin     flightless black-and-white bird native to the far Southern Hemisphere, especially Antarctica and its nearby islands.

prey     (n.) Animal species eaten by others.

propulsion     The act or process of driving something forward, using a force. For instance, jet engines are one source of propulsion used for keeping airplanes aloft.

sensor     A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.

tagging     (in biology) Attaching some rugged band or package of instruments onto an animal. Sometimes the tag is used to give each individual a unique identification number. Once attached to the leg, ear or other part of the body of a critter, it can effectively become the animal’s “name.” In some instances, a tag can collect information from the environment around the animal as well. This helps scientists understand both the environment and the animal’s role within it.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

whale     A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.

Citation

Journal:​ ​​P. Serge et al. A hydrodynamically active flipper-stroke in humpback whales. Current Biology. Vol. 27, July 10, 2017, p. pR636–R637. doi: 10.1016/j.cub.2017.05.063.