As winter approaches, most animals can avoid the cold by migrating or hibernating, but what about the ones that cope with the freezing temperatures? In the frosty depths of the Petitcodiac Watershed lies a hidden world teeming with life, where survival hinges upon the delicate mix of freezing temperatures and unforgiving conditions. From the smallest invertebrates to the mightiest fish, each organism has honed its own unique strategies to endure the frigid depths and thrive amidst the challenges of the season. To survive these conditions, acclimation is not merely a luxury but a necessity for creatures to navigate the icy waters with resilience. The ability of aquatic life to endure and thrive in winter’s adversities is truly impressive and showcases the evolutionary challenges they have overcome. Let’s discover some of these aquatic animals that can be found in the Petitcodiac Watershed!  

Photo by Claire Johnson 

It is important to first note how water properties work. Water will often have stratification, layers of water at different depths that are defined by a property such as a temperature gradient. In the summer, this gradient has warmer water on the surface and colder water will sink to the bottom, but in the winter, it is the opposite. This is because water is most dense at 4°C, so this warmer water sinks allowing less dense colder water that freezes at 0°C to create a layer of ice on the surface which acts as an insulator to the water beneath, so it does not always freeze solid to the bottom. The thermocline is a transition layer that separates the two water layers that differ in temperature in both summer and winter.

Summer vs winter temperature stratification.

In frozen rivers, fish employ various strategies to endure the harsh conditions to ensure survival. Fish are cold-blooded, so when temperatures plummet and the ice encases the water’s surface, many fish species enter a state of dormancy as their metabolic rate decreases significantly, allowing them to conserve energy. Some species, like certain trout and salmon found in the Petitcodiac watershed, seek out deep pools or areas with faster currents where the water does not freeze and remains relatively warmer with higher oxygen levels. Others may bury themselves in sediment at the river bottom or find refuge beneath ice shelves, utilizing these insulated spaces to shield themselves from the freezing temperatures. During this period of rest, fish will reduce their heart rate and partake in minimal movement to conserve energy to decrease and even eliminate requirements for food. They will even orientate themselves to allow the flow of the current to pass oxygen against their gills to enhance gas exchange efficiency when stationary.  

Atlantic Salmon. 

Macroinvertebrates, tiny aquatic insects that are important bioindicators of water quality and stream health of watersheds, have some very fascinating strategies to cope with the cold. Unlike others, stoneflies stay active to keep themselves warm and take advantage of and prey on insects that hibernate. They can live in the ice as they produce antifreeze-like sugars allowing their body temperature to drop to –4°C without freezing! Snails will burrow into the mud to take advantage of geothermal heat for about three months or until they can sense the change in moisture in the soil when it thaws. Freshwater mussels are also known to bury themselves in the mud to prevent getting frozen. Midges slow their movement and like stoneflies produce proteins that act like an antifreeze to stay alive. Aquatic worms have an interesting ability to form a chrysalis, a hard casing they produce and enclose themselves in to protect them from winter conditions, and then emerge back out in the spring!  


Wood turtles survive winter by crawling into log jams or tree roots underwater to hide from predators in oxygen-rich pools, where they enter a state of dormancy, slowing down their metabolism to conserve energy until the arrival of warmer temperatures. This leaves the question; how do they breathe without gills? They can absorb oxygen directly from the water through capillary beds on the roof of their mouth and their cloaca (their butt!), a very gassy animal indeed.  

Wood turtle. Photo by John Kleopfer/ VDWR. 

Many mammals hibernate during the winter, but not the busy beavers. Beavers are ecosystem engineers as they build strong insulated dams made of wood and mud partially submerged in the river with an elevated ‘dry room’ where the family cuddles together exchanging body heat to survive the cold temperatures. Beavers will accumulate up to 60% extra fat in their tails to store energy needed for harsh winters and they reduce their activity to preserve it. Beavers also have excellent built-in waterproof blankets as their fur grows thick in the winter to insulate their body heat and has water-resistant properties due to oil secreted from their skin.  

Beavers foraging. Photo by Ann Brokelman. 

These remarkable behaviors and adaptations collectively enable aquatic animals to withstand the challenges of frozen rivers and emerge resiliently as the thaw of spring approaches. However, with our winters becoming inconsistent due to climate change, it has raised concern about how it may affect the ability of these animals to cope with fluctuating temperatures posing false springs and offsetting the time of emergence and underlining physiological and behavioral shifts.  


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