With thoughts of Michigan’s General Trout Season opening April 25th, thought has to be given to winter fish kill: Will the 2nd harsh winter in a row have a devastating effect on trout populations in our native trout waters? Most, if not all, of our trout streams were frozen from bank to bank in some parts and that’s not good for trout, the most sensitive species of all where winter kill is concerned due to a lack of oxygenated water.
The following was taken from the Michigan Department of Natural Resources website:
Actually, the fish suffocated from lack of dissolved oxygen. Trace amounts of dissolved oxygen (measured in parts per million, ppm) are required by fish and all other forms of aquatic life. Even living plants and the bacteria that decompose organic materials on the bottom of the lake require oxygen. As a rule of thumb, the critical level of oxygen is about 2 ppm for most game fish native to warmwater lakes, and levels below 1 ppm for extended periods of time are lethal.
But species of fish vary in their tolerance of low oxygen. Trout are most sensitive; walleye, bass, and bluegill have intermediate sensitivity; and northern pike, yellow perch, and pumpkinseed are relatively tolerant. Bullheads and certain minnows are very tolerant. Lakes prone to periodic winterkill can often be detected from the composition of their fish populations – tolerant species predominate, sensitive species are rare, and prey greatly outnumber predators. Fortunately, usually enough fish survive, either in the lake or in connecting waters, to repopulate the lake in a couple of years. Only for extreme die-offs is fish restocking necessary.
Here’s hoping the trout populations in our fabled rivers survived.