Fighting the Freeze: How Do Water Animals Survive the Winter?

Most animals have three choices to survive winter: migrate, hibernate, or cope with freezing temperatures. Many birds (and some humans) choose to migrate south to warmer places. Bears fatten up and sleep through winter in their dens. But aquatic animals have an extra challenge: freezing water. Few animals can withstand being frozen because the forming ice destroys cell membranes, so aquatic animals have “cool” adaptations.

Western Painted Turtles breathe through their butts.
Painted turtles live in ponds and wetlands throughout the Elk Valley. As these waters freeze, turtles gulp their final breaths and sink to the bottom. Here, water stays near freezing, but still liquid. Unlike mammals and birds, whose body temperature is kept stable by burning energy, turtles are “ectotherms” (aka cold-blooded), meaning their body temperature is determined by the external environment. Their metabolism drastically slows to a heart rate of 8, slow, steady, beats per hour, which decreases energy use.

Because turtles can’t resurface for air, they use highly vascularized areas of their bodies–their butts–to extract oxygen directly from the water. But even this is not enough, and lactic acid starts building up in muscle tissues. To deal with this, turtles use the calcium carbonate in their shells to neutralise the acid (much like we take calcium carbonate pills like Tums to deal with heartburn). As spring waters warm up and ice melts, turtles swim up to the surface, breathe their first breaths, and start basking in the sun.

Stoneflies are supercool.
Stoneflies thrive in Elk Valley rivers and streams and spend up to three years being an aquatic nymph stage. They are cool bugs, but in the winter, they become ‘supercool!’ ‘Supercooling’ is a process by which water temperature drops below 0°C but does not freeze. This happens when water is free of any particles around which ice formation can begin, or when water has chemicals with “antifreeze” properties. Stoneflies produce glycols and sugars which act as antifreeze, and this allows their body temperature to drop to -4°C without freezing. 

Trout chill out at the bottom.
Like turtles, trout seek waters that stay liquid in the dead of winter. Studies where fish were radio tagged, showed that trout move dozens of kilometres to find deep pools with plenty of woody cover and large boulders. This habitat is essential to trout survival and restricting or removing access to this habitat can have drastic consequences. In 2019, Teck reported a 93% decline in Upper Fording juvenile trout, compared to 2017. This intense population drop was highly worrying, and several outlets suggested that it was due to excessive selenium pollution from mine sites. However, after investigation, a 2021 report found that the most likely reason for this decline was that mining operations altered the stream to such an extent that fish had difficulty reaching their overwintering sites, leading to high mortality during a harsh winter. 

Beavers waterproof their fur.
Beavers, like us, are mammals and must work hard in the winter to maintain an internal temperature of 36°C. To do this they snuggle up with their family, cozied in dens. Occasionally, they brave the cold to collect food stored outside their den. To insulate their bodies from the harsh elements, beavers have a dense fur, with a second, longer layer of guard hair fur overtop. Air is trapped between these two layers, and acts as an insulator which prevents rapid heat loss. On top of that, glands near the beaver tails produce a water-resistant oil which beavers diligently preen throughout their fur. This waterproof coat keeps them nice and warm even as they swim through near-freezing waters.