Provincial authorities are asking anglers – or anyone out enjoying the great outdoors for that matter – to report any fish kills seen on lakes throughout Alberta following spring ice break-up.
Jim Stelfox, senior fisheries biologist with Alberta Sustainable Resource Development, said recently the long, cold winter could have led to overwinter fish kills, especially in shallow lakes.
Of particular concern in the Rocky Mountain region are Sibbald Lake, Sparrow’s Egg Lake and Champion Lakes in Kananaskis Country and Margaret Lake in the Ghost-Waiparous region.
However, other shallow lakes throughout the region could be at risk, as well.
Stelfox said overwinter fish kills occur when lakes do not have adequate oxygen to carry a population of fish through the winter until ice breaks up in spring.
As part of the winterkill scenario, other factors that affect fish survival include ice clarity, snow cover and the amount of wind in fall, which adds oxygen to a lake before a lake freezes.
“So much depends on how much wind is occurring at the right time. The longer you have a period of time where lakes are ice free in the fall and the temperature is fairly uniform throughout the water column, the more potential to get turnover on the lake. That turnover is really important for the lakes,” Stelfox said.
Generally, spring-fed lakes fare better as oxygen is added to the water throughout winter.
Fish face a worst-case scenario if the weather shifts quickly from a warm spell in fall into a cold spell with little or no wind as lakes go into winter with less oxygen.
“The colder, denser water isn’t going to rise to the surface and mix with the upper water unless you had one heck of a wind blowing,” he said.
But with a good fall and slowly decreasing temperatures, similar to what occurred last fall, the temperature of the surface water drops to about the same temperature as water in the lower levels, which in effect removes the blanket keeping the two layers separate, allowing them to mix easily.
A blowing wind can then turn or roll the water over, which allows oxygen-poor water at the lower levels of a lake to come to the surface where it will release carbon dioxide and absorb oxygen.
While ice depth isn’t necessarily an important element in overwinter fish kills, the clarity of the ice and whether or not it is covered in snow can either permit photosynthesis in aquatic plants, which can put oxygen into the water, or block it, causing plants to consume oxygen.
Decomposing plant matter will also consume oxygen.
Knowing if a lake experienced overwinter fish kills can help land managers and fisheries biologists make informed management decisions, Stelfox said, such as understanding which sport fishing lakes need to be restocked.
To report overwinter fish kills in this region, contact Stelfox at 310-0000, followed by 403-851-2205.
