Drafting Dolphins Ride the Wakes with Ease
Pennisi, Elizabeth, Science News
As a swimming instructor, Terrie M. Williams found the awkwardness of the human body in water quite frustrating. So when she became a wildlife physiologist, she decided to study just how efficient marine mammals are in their aquatic endeavors. And when she looked at the vital signs of dolphins trained to swim alongside a moving boat, she discovered that they owe their smooth technique not only to their streamlined shape but also to where they swim.
For fast speeds, the animals shift positions to take advantage of the physics of the water, moving along with no apparent effort, Williams and her colleauges report in the Feb. 27 Nature.
Working at the Naval Oceans Systems Center Hawaii Laboratory in Kailua, the researchers equipped two bottlenose dolphins with harnesses that monitored the heart rates of the free-swimming animals. The team also measured the lactic acid buildup in the animals' blood and counted how often the dolphins surfaced to breathe.
Traveling at 2 meters per second, the dolphins used about 1.3 joules of energy per kilogram of body weight; their hearts beat about 76 times a minute. That makes them twice as energy efficient as seals and sea lions and about 10 times as efficient as humans, Williams says.
When the boat sped up to 3 meters per second, the dolphins seemed to strain a little, but they still swam out to the side as trained. …