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Under the ice, local fish & amphibians wait for spring

MEREDITH — During a typical New Hampshire winter, lakes and ponds are sealed off from the rest of the world with a thick layer of ice. The aquatic organisms that were not able to go south in search of warmer waters face the challenge of adjusting to water temperatures low enough to freeze their homes and declining levels of oxygen. To deal with these adversities, frogs, turtles and fish have adapted many unique strategies which allow them to survive.

As the air temperature drops throughout the fall, the body temperature of frogs and other amphibians and reptiles drops as well, alerting them to head for their overwintering site. Some frogs overwinter by burrowing down in the thick layer of decomposed leaves along the shoreline where their bodies may partially freeze. They don't freeze completely, however, thanks to a high amount of glycerol or glucose that their bodies produce which acts like antifreeze. Other amphibians and reptiles that cannot tolerate freezing spend their winter at the bottom of the lake in the mud where the ice can't reach.

Most turtles burrow into the mud and become inactive during the coldest winter months. However, some turtles have an unusual ability to survive very long periods of time without oxygen—in fact, their metabolism can continue uninterrupted without needing oxygen. These turtles enjoy their normal activities throughout the winter.

Like other cold-blooded animals, fish adjust their body temperature to decreasing water temperatures and can modify their metabolism to tolerate the cold. Some fish are able to reduce the amount of fat in their bodies and, like frogs, produce an antifreeze-like substance inside their bodies—trout, salmon, and yellow perch are particularly good at this. This allows them to remain active during the winter, but their movements are slow. These fish often migrate to the deepest part of the waterbody where the water is the warmest. Other fish, such as bass and sunfish, which are unable to tolerate the cold water, spend the winter in a resting state by burying themselves in the mud and leaves at the edge of the waterbody. Amazingly, bullheads, and other members of the catfish family, can completely freeze during the winter and thaw in the spring without being harmed.

Although, the activity level of these cold-blooded aquatic animals drops during the winter, it typically does not stop entirely. Instead of going into a constant state of inactivity commonly referred to as 'hibernation' like some warm blooded animals, certain fish, and many turtles and frogs go in to a period of reduced activity called 'brumation.' During a warm spell, like a January thaw, they may get heated up enough to venture out of their winter home.

The biggest threat to the aquatic organisms that stay behind in New Hampshire each winter is not the cold weather—it's the loss of winter habitat. Man-made alterations along the shoreline can prevent frogs and other amphibians and reptiles from reaching their vital overwintering habitat on land. Water level draw downs conducted too quickly during the fall can strand organisms out of the water before they are able to relocate to their overwintering site, causing them to perish.

The Meredith Conservation Commission will meet on the first Thursday of every month at the Meredith Community Center at 7 p.m. Additional information about the work of the committee is available at meredithnh.org. or can be obtained by calling 226.0299.

 

 
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