Resilient Residents – Frosty Fish

Resilient Residents – Frosty Fish

This is the last of a four part series on our province’s most resilient animals. You can find out more about mammals that are active through the winter here, about mammals that are inactive but don’t hibernate here, or about birds that stay in the province over the winter here.

While mammals may burrow or hibernate, and birds can be seen shivering away on a branch, the average Albertan never sees what happens to fish during the frigid days of winter.

Frozen lakes and rivers may give the appearance that its inhabitants are inactive, but that isn’t the case. Under the ice, in the flowing water and in the lakes, many of Alberta’s fish thrive as long as the conditions allow.

The cold-blooded truth

Fish are cold-blooded, meaning that their body temperatures vary with the surrounding temperature. During the cold of winter, fish become less active. They find little pockets out of the way of fast moving water where they can stay still and conserve energy. As their metabolism slows, they eat less and wait out the coldest part of winter.

The most important habitat feature for overwintering fish is water depth. Pools in rivers or areas of lakes need to be deep enough to avoid freezing. Although this seems obvious, it doesn’t mean that these sites are always readily available.

A breath of fresh…water?

Another important factor is dissolved oxygen, which all fish require. Other members of the aquatic community, including invertebrates and most types of bacteria (that breakdown organic matter), also require dissolved oxygen.

But when a body of water is completely covered in ice, oxygen from the atmosphere cannot reach the water. Over time, dissolved oxygen gradually decreases. In some cases, this can lead to waterbodies in which all the fish die.

In lakes where fish are stocked, oxygen levels are monitored and an aerator may be used to increase oxygen levels if required.

Survival of the finnest

Northern Pike are some of the most active fish in the winter. They are well adapted to the climate, both in their ability to slow down their metabolism to deal with lower-oxygen environments, and their ability to deal with chilly water. They feed on minnows throughout the hard-water season. Their ability to survive the coldest waters is one of the reasons they’re found throughout Alberta.

Walleye are aggressive feeders in the winter months. They prefer to stay in the same places as they spend their spring and summer, but they move to deeper areas to get to cover.

Most of us are waiting for May when warm weather brings out all of  Alberta’s diverse wildlife. In the meantime, we hope you enjoy the presence of those animals that braved the winter. Why not try some ice fishing this Family Day, and try to imagine the complexity and challenges of the aquatic environment? It’s free family fun and you’re sure to catch a memory!

Source: Alberta Environment and Parks