Montana Winter Fish Kills

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During the 2010-11 Winter season, Montana Fish, Wildlife & Parks (FWP) officials noticed yellow perch struggling and many others dead at the bottom of their holes.

Winter fish kills are common in small prairie ponds in Eastern Montana, especially shallow ponds that have abundant aquatic vegetation. There are several mechanisms that can contribute to a winter fish kill. Drastically reduced dissolved oxygen levels occur when snow accumulates to a point where little light can penetrate the ice, which in turn stops photosynthesis, a process that produces oxygen as a byproduct.

Another mechanism is when large amounts of vegetation that have accumulated in a pond through the summer growing season begin to die and decompose. The decomposition process uses a lot of oxygen from the water. When both large amounts of vegetation are decomposing and snow accumulates, the result can be a significant fish kill.

While little can be done to help the fish population in Whitetail Reservoir this winter, FWP will sample it early this spring to get a better understanding of the loss. If only a small number of fish made it through the winter, FWP will transport adult yellow perch into the reservoir with the goal of rebuilding the perch population.

Long-term plans will need to address what can be done at the 25-acre reservoir — which also has been home to black crappie, northern pike and walleye — to make it more sustainable through these tough winters.

For questions or concerns about Whitetail Reservoir or other ponds where the public has observed significant fish kills, please contact FWP’s Region 6 office in Glasgow at 228-3700.