Dolphins, whales, and other marine mammals keep warm with a thick layer of fat under their skin. This blubber also improves their buoyancy. Now, studies of trained dolphins suggest an additional function: Blubber turns the dolphin's tail into one long spring that helps it swim efficiently.
Researchers have known for some time that terrestrial animals often make use of springs: Kangaroos--or even humans--store energy in leg tendons that, when released, helps propel the body into the air. Many scientists have hesitated to consider that springs might aid swimming, however, because gravity, which plays a role in the springlike activity of creatures with legs, has little effect on organisms suspended in water. Instead, muscles were thought to provide all the power for swimming. But work in some invertebrates, such as squid, and some fish suggested otherwise. Now dolphins can be added to the list.
The idea that the dolphin tail could provide elastic energy springs in part from work by Jonna Hamilton, a graduate student at the University of North Carolina, Wilmington. Working with functional morphologist Ann Pabst, she found that the blubber midway along a porpoise's body is relatively stretchy. In contrast, blubber near the end of the tail, or fluke, is three times stiffer. As with humanmade composite materials, this range of properties sets the stage for the tail to work like a spring. In tests with trained dolphins, they observed that the stiffer blubber hardly bends at all, while the blubber closest to the dorsal fin bends quite a lot, reaching its maximum distortion at the bottom of the tail's downstroke and then bouncing back. They reported their findings last week at the annual meeting of the Society for Integrative and Comparative Biology in Atlanta.
Besides helping biologists better understand how whales and dolphins get along in their watery world, the results "tell us about how to make things," says Steve Nowicki, a comparative integrative biologist at Duke University in Durham, North Carolina. Pabst agrees. In fact, Peter Wainwright of Duke University is building a new kind of underwater craft, one with a flexible propeller modeled after the dolphin's fluke. And the U.S. Navy is interested, too, Pabst and others note, because of the potential to build quieter, more fuel-efficient submarines.