FISH KILL - SEPTEMBER 2024
It’s possible that many of you noticed an unusual number of white, medium size fish floating up on your beach dead this late summer and early fall. We contacted the DNR and found out about this phenomenon that occurs occasionally. In fact they investigated a Cicso kill on Pine Lake in 2009 after an abnormally warm first half of September. Here’s the gist of what they had to say...
In a nutshell Cisco are very sensitive to oxygen levels and temperature. Many fish are much more tolerant to changes in these, but not cisco. Cisco need cold water less than 73 degree Fahrenheit and high oxygen levels greater than 6 mg/liter.
Lakes in Wisconsin “turnover” in the spring and fall when water temperatures are the same top and bottom (~50 degrees). This allows the water to be mixed and oxygen added. As waters warm during the summer the area in the lake where temperature and oxygen is sufficient for cisco survival gets smaller and smaller. As the summer progresses oxygen gets used up in the lower part of the lake. This forces cisco higher and higher in the water column into warmer and warmer water. As cisco are forced into this warmer water they get stressed and eventually die. On a typical year our temperatures start to cool by this time and cisco can handle being higher in water column and eventually turnover happens and their livable area expands to most of the lake.
So if our climate is truly warming and our warmer than average temperatures continue to last further and further into September/October the presence of cisco in many of our lakes including Pine is going to challenged.