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What happens to trout in the winter?


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Interesting article by TUC's Lesley Peterson in Cows and Fish Winter 2023 Newsletter:

What happens to trout in the winter?

by Lesley Peterson of Trout Unlimited Canada



As fall turns to winter, many of us hunker down and get cozy. We spend a little less time outside in the cold, and more time in the comfort of our climate controlled houses and offices. Animals deal with winter in all kinds of different ways. Some birds fly south to warmer climates; some critters hibernate; and some just carry-on with their lives thanks to cold-weather adaptations.

But what do trout do in the winter?

Fish have evolved traits to help them survive the harsh conditions of winter. For starters, trout are poikilothermic, meaning they are cold-blooded and their body temperature changes with their environment. This means that they do not have to spend energy to maintain a certain body temperature, which is good because food availability is limited in the wintertime.

Have you ever been catch-and-release fishing for westslope cutthoat trout at an alpine lake and found them highly “catchable”? Some people may think these fish are “dumb” for being easy to catch. In reality, these fish have evolved to take full advantage of what is typically a very short open water season in the mountains by eating as much as possible before a long winter with limited food availability. Seems pretty smart after all!

Besides challenges with food availability, fishes’ ability to move from one habitat to another may also be limited because of the effects of ice or low flow conditions. In streams, where many of Alberta’s native trout live, habitat can be highly variable and, in the winter, ice can have a big influence. For example, there is a phenomenon known as “supercooling” when water cools below 0°C but remains liquid. Ice crystals can form into a suspected slush known as frazil ice that sticks to hard surfaces. When frazil ice sticks to the bottom of a shallow stream it becomes anchor ice and can form a temporary dam, resulting in flooding, which may force fish to move from one holding area to another.



Generally, many fish will retreat to deep pools or areas with groundwater upwellings in the winter. Theses spaces provide some stability in terms of flow, temperature, and oxygen, helping fish to minimize their movements and energy expenditure. Smaller fish such as juvenile trout will often seek out cover between the spaces of coarse rock substrate and boulders. But it’s not just fish that have to make it through the long, dark winter. For fall spawning species like bull trout, their eggs remain protected within redds (trout nests in the gravels) all winter, emerging in the spring when temperatures warm.

So what can you do to help our native trout get through the winter?

  • Respect seasonal fishing closures that not only protect fish during a vulnerable time
  • Keep wheels out of water to avoid trampling incubating eggs
  • Participate in volunteer stream and riparian restoration projects improve the health, complexity, and connectivity of streams, ensuring fish have access to a wide variety of habitat types including overwintering pools
  • Keep beavers on the landscape to maintain year-round water in what might otherwise be dry stream corridors; beaver ponds can also make excellent overwintering habitat
  • When ice fishing, avoid letting fish be exposed to the air as much as possible and never place the fish directly on the ice or snow

Visit Trout Unlimited Canada’s blog to learn more about lakes and rivers in winter and how fish survive.

To learn more about how you can help stand up for native trout, visit www.albertanativetrout.com.

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