Plump turtles swim better: study

Longer, slender turtles are less efficient swimmers than their more rotund peers, a new study has found.
For the first time, researchers at the University of Wisconsin-Madison, Florida Atlantic University (FAU), and the National Oceanic and Atmospheric Administration (NOAA) have measured the forces that act on a swimming animal and the energy the animal must expend to move through the water.
They found that longer, slender turtles are less efficient swimmers than more rotund turtles, which get better stroke for their buck.
Several labs have tried to model the movements of animals in water but "swimming animals are very, very difficult to measure experimentally," said Warren Porter, a professor of zoology at UW-Madison's.

No one before had been able to measure the fluid dynamics of a swimming creature, or the energetics required to perform the work of moving through water.
This allows scientists to measure critical aspects of biology, such as how much food an animal must eat to survive.

Jeanette Wyneken, FAU professor of biological sciences, had earlier developed methods to keep newborn leatherback sea turtles in the lab for study.
She and her former students created a tether system that allows the turtles to swim freely while also staying safe; the turtles don't recognise barriers and can easily injure themselves in their enclosures.

Porter and Peter Dudley, lead author of the study, a former graduate student in Porter's lab, and Todd Jones - Wyneken's former graduate student and now a NOAA physiologist - tethered the turtles to instruments that allowed them to measure the force they produced while swimming.
They also measured the oxygen the turtles consumed (a direct measure of their metabolism) and the heat they exchanged with the environment. All the while, the scientists took video of the tiny turtles.
Then the team recreated a virtual environment with a swimming turtle, to see if they could predict how much energy the turtle was using.

Researchers then modelled the three-dimensional motion of swimming juvenile leatherback sea turtles, to find power and heat transfer rates during the larger animal's flipper strokes.
It was here, by playing with the parameters of their virtual reality turtles, that the researchers learned husky turtles were better swimmers than their leaner counterparts.
"That was a surprise and I thought it was a mistake when I originally did it," says Dudley, who eventually learned that the flippers of thinner turtles come closer together at the bottom of their stroke than those of larger turtles, causing them to lose power.
"We can literally design animals now and ask how are they going to function, just like a car or a rocket ship," said Porter.

The findings are published in the journal PLOS One.