The Impact of Heavy Snow and Ice on Montana’s Winter Fish Kills
Is it possible to have too much of a good thing? Fish that thrive in shallow ponds and lakes might tell you that it is.
It has been a pretty tough Montana winter so far. The long-term gains we hope for are plentiful water supplies in our lakes and rivers and reduced fire dangers this summer. And while thick ice and steady snow cover can create excellent ice fishing conditions, they can put additional strain fish on fish populations in waters that are prone to winter kill.
Montana Fish, Wildlife and Parks shared with us a brief overview of the impact a winter such as this one might be having on certain fish populations. For some, it's business as usual. But there are areas of concern, too.
What Are Winter Fish Kills?
Montana FWP says that "most winter fish kills are natural events that occur when a waterbody is sealed off by ice and snow, preventing oxygen exchange between air and water and blocking the sunlight necessary for photosynthesis.
"The process of photosynthesis produces dissolved oxygen that is necessary for fish to breathe. Dissolved oxygen concentrations begin to decrease from the lack of sunlight and as vegetation breaks down in the water. Declining oxygen levels can lead to fish stress and, ultimately, fish mortality."
So, while fish kills are more likely during harsh winters, those declines in oxygen where there is shallow water combined with abundant vegetation don't harm a body of water's entire fish population. In fact, the impact may go completely unnoticed.
Most of the time, these oxygen “sags” do not occur in the whole waterbody and do not harm the entire fish populations. These incidents may go completely unnoticed.
But Then, Sometimes They ARE Noticeable
An example Montana FWP used was a recent call from some anglers reporting a winter fish kill at McWenneger Slough near Kalispell. Even though fish kills are common in northwest Montana, FWP biologists investigated and found low levels of dissolved oxygen in the slough, confirming the cause of the natural fish kill. The dead fish included yellow perch, pumpkinseed, crappie, and northern pike.
What Can Anglers Do?
While it may be nothing more than the natural course of nature, Montana FWP appreciates being contacted, as in the case of the McWenneger Slough fish kill. Notify your local FWP office with information on your location, the date, the type of fish and numbers you see, and maybe even some photos if possible. This information is a huge help to biologists trying to determine if the event was natural or perhaps the result of human actions.