Take half a dozen retired Navy dolphins and put them in a huge tank with a trainer and some oversized hula hoops for six months and what do you get? Potential clues to unraveling the mysteries behind why some marine mammals are susceptible to mass strandings, scientists hope.
In a study published Wednesday in The Journal of Experimental Biology, scientists showed that dolphins and whales used more energy to swim fast than to cruise at normal speeds. This may seem obvious, but marine mammals aren’t supposed to get tired swimming. We have assumed that these master divers have adapted physiological workarounds that help them conserve oxygen and energy. And most of the time, they have. But this study suggests that vigorous swimming to avoid threats — posed by people as well as predators — could come at a cost to mammals that live in the seas.
Terrie M. Williams, who studies ecophysiology at the University of California, Santa Cruz, and her team worked with trainers to encourage the dolphins, as well as one retired theme park killer whale, to perform a variety of behaviors in large saltwater tanks. Some animals would rest at the surface or submerged, move in a straight line across a pool, cruise the perimeter or dive down to swim through hoops placed in different arrangements at the pool’s bottom. To the sound of a whistle, they surfaced beneath a special hood and inhaled air while Dr. Williams measured their breathing and oxygen intake. Across a variety of settings, she also measured heart rate, the frequency and amplitude of swimming strokes and swim gait.
Her team found that there was not a big difference between the energy the animals used at rest and while swimming at average speeds that range somewhere from 5 to 8 feet per second, according to the study. But drag in the water that increases with speed makes the cetaceans exert more energy as they move faster; the dolphins nearly doubled their normal energy use when swimming their hardest.