Sink or Swim

If you have been lucky enough to watch a turtle in a glass aquarium, you saw that turtles are strong swimmers, but sometimes they just hang out on the bottom. For you to do that, at the bottom of a pool, for instance, you would need two things: a way to breathe and something heavy to keep you down there. How does a turtle stay under, perhaps even napping?

painted turtle in aquarium floating just below the surface

Educational ambassador Diane demonstrates how turtles can float just below the surface.

In our last post about turtle physiology, we noted that, because of the shell, turtles have significantly more bone mass than other animals. That heavy bone sinks like a rock. But turtles can also float, so something must be making them buoyant.

We have seen turtles described as little submarines. That is a pretty accurate comparison. Turtles sink or swim like submarines dive or surface except, instead of ballast tanks, a turtle has a bladder.

To counteract the weight of their shells and float, turtles pump air into their large lungs. To submerge, they draw water into the urinary bladder through the cloaca. How deep a turtle stays depends on the ratio of air in the lungs to water in the bladder. There are variations in this depending on the species of turtle, but that is the general idea.

Having all that air in their lungs, plus slow metabolism, means a turtle can hold their breath a long time. Under normal summer conditions, it might be an hour before a turtle comes up for air. Napping, the turtle might stay even longer. And if the oxygen in the lungs gets used up before the turtle surfaces, they will switch to anaerobic metabolism and not need any oxygen at all. But that is a story for another time.

You can learn more about how turtles sink or swim in our educational outreach programs. We are always looking for new program hosts. Please contact us to bring a program to your school, library, or club meeting.