Imagine it’s winter, and you’re standing on a frozen lake or pond, when suddenly below your feet you notice hundreds of turtles. What are they doing down there below the ice?

Freshwater turtles in temperate regions like Canada spend several months of the year braced against frigid winter conditions of temperatures around or below 0 degrees and the formation of ice on water bodies.

For all eight species of freshwater turtles in Canada, this ice barrier — and more importantly the liquid water below it — is a refuge from the freezing temperatures above. While ice coverage protects these turtles from the harsh cold, it also presents them with a challenge: restricted access to atmospheric oxygen.

Some species, like snapping turtles (Chelydra serpentina) and painted turtles (Chrysemys picta), are perfectly comfortable spending several months submerged in water depleted in oxygen. However, some species do not fare as well without oxygen and can only survive a few weeks at a time if submerged without adequate oxygen. These species need to extract the oxygen dissolved in the water to survive.

The northern map turtle (Graptemys geographica) is an example of such a species. They have also been observed engaging in locomotor activity — they keep moving around under the ice during the winter.

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