The ice abides: Turtles in winter

On my winter walks on the Birch Lake ice I come upon fallen logs where, in summer, painted turtles line up to sun themselves.

You may have asked, “Where do the turtles go in winter?” And that’s an easy answer, right? To the lake bottom, to hibernate. But then, we know turtles aren’t like fish. They spend a lot of time underwater, it’s true, but they don’t have gills. They need to surface to breathe; we’ve seen their snouts poke up in calm water, then disappear.

So, if in summer they need to surface every so often for a breath, how do they survive under the ice for, say, four to five months with no access to the air? It turns out they actually can breathe down there – though not with their lungs, by way of the snout. And they need very little oxygen to make it through the winter, because their metabolism slows to almost nothing. 

At the lake bottom, the winter water temperature hovers around 4 degrees C (39 degrees F). Since turtles are cold-blooded, that becomes their body temperature. They become extremely sluggish; if they crawl or swim at all, it’s very slowly. Their hearts slow down to as low as one beat every ten minutes. They eat very little, if at all.

Yet because their body functions don’t shut down completely, they need oxygen. They get it from the oxygen dissolved in the water. It enters their bodies through the linings in the mouth and throat, and through two small sacs near the anus with very thin skin, laced with numerous tiny blood vessels. They could never survive breathing this way in summer, when their metabolism is high, but in winter, it’s enough. ← Larry the Bullfrog speaks about living in Wisconsin

Ice Fishing Contest on the St Croix Flowage Saturday, January 19 →

So unless we go through a winter of truly epic proportions, there will be enough oxygen in the water for turtles to survive. And next summer we’ll see them again, sunning themselves on those same old fallen logs.