Graptemys

• Imagine it’s winter, and you’re standing on a frozen lake or pond, when suddenly below your feet you notice hundreds of turtles.
• While ice coverage protects these turtles from the harsh cold, it also presents them with a challenge: restricted access to atmospheric oxygen.

Life under ice

• 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.
• They have also been observed engaging in locomotor activity — they keep moving around under the ice during the winter.
• Northern map turtles were observed over a century ago by marine biologists Barton Warren Evermann and Howard Walton Clark.

Advances in technology

• These devices recorded the movement, depth and temperature of the turtles for the seven months they remained under the ice.
• Tri-axial accelerometers function similarly to a FitBit or Apple Watch — the devices produce a value called overall dynamic body acceleration.

Daily movement

• The data showed that northern map turtles move, albeit locally, every day of the winter.
• While that may look different across individuals, the interesting thing here is that movement is indeed continuous throughout the winter and not that different than in the weeks before the ice locks them in for the winter.
• Although we expected some level of activity based on previous observations, we did not expect the turtles to be so fidgety all winter long.

Implications of movement

• Small amounts of activity may allow this species to replace the oxygen-depleted boundary layer of water on their skin with freshly oxygenated water.
• Alternatively, movement may be necessary for turtles as they look for micro-climates within their environment that have higher concentrations of oxygen or preferred temperature and depth profiles.
• In doing so, map turtles may be able to better need their physiological needs and oxygen requirements through the entirety of winter.