The winter of 2013-14 has been long and harsh, as witnessed by the foot-plus of mid-April snow we received last week. Many Copper Country residents have seen or experienced a case of TMS syndrome (too much snow) this winter, which is not to be confused with other syndromes. Well, our lengthy winter is not done giving, as you will see, if spring ever arrives. Perhaps if we all stand, click our heels together, and chant "I wish it was spring, I wish it was spring, I wish it was spring"
As spring ever so slowly approaches and local lakes/ponds thaw, my prediction is, our long, severe winter has caused significant fish mortalities. How, you ask? There are factually three kinds of natural fish kills, which are all weather related. Winter kill, spring kill, and summer kill. We will focus on winter kill.
Winter kill is the result of a significant decline in oxygen (O2) levels during the time a lake or pond is ice covered. During the winter more O2 is used by aquatic animals, mainly fish and decomposing plant material (leaves, aquatic vegetation, etc.) from the previous summer, than is made. During winter ice/snow cover, O2 made from photosynthesis from green plants is greatly reduced. This is especially true in years of many feet of snow and bitter cold, which enhances ice production, as sunlight cannot penetrate into the water. Several anglers have told me there was three-plus feet of ice on Chassell Bay this year.
A serious problem develops when winter drags on, like our current condition, as the use of O2 goes on. If O2 levels reach 2-3 parts per million (ppm) some fish will die. If the levels get down to 1-2 ppm most fish will die. The volume of water in a lake or pond also is a factor. Lakes and ponds that average five to ten feet in depth will totally winter kill in a year such as we have had. Several area lakes in this category are Bear Lake, Rice Lake, Sandy Lake, and Toivola Lakes No. 1 and No. 3, which are in Houghton County. Keweenaw County lakes include Deer Lake, Lake Bailey, No Name Pond, Schlatter Lake, and Thayer Lake.
Even though a pond or lake is spring fed, that does not make it immune from winter kill. Springs or ground water are basically devoid of O2, containing about a half a ppm. Once it bubbles or is exposed to the air, it quickly becomes saturated with O2. So, unless your farm pond has open water from a spring, it is subject to winter kill.
Lakes/ponds that have water depths of 20 feet or less are also likely to experience some level of winter kill this year. The level of fish mortality will depend on the number of fish and the amount of plant material decomposing. In addition some species of fish can tolerate lower levels of O2. Bullheads and carp are two such species that can live in 2-3 ppm O2. Bass, pike, and trout need O2 levels of at least 4 ppm.
Advice to cottage owners: When the ice finally melts and you see dead fish, do not be concerned your lake or pond is polluted, winter kill is the cause. This will save you a call to the Fisheries Division, DNR or the Health Department. However, if you feel the fish mortalities are not natural, please contact your local DNR office or conservation officer.
Summer kill in lakes or streams can occur during extremely hot summers. Pike, perch, bass, suckers, and bluegill in shallow lakes and bays with excessive plants or algae are vulnerable. In these water bodies, green plants make O2 during the daylight hours, but at night they use O2. The O2 levels can go from a super saturation of 13-14 ppm in the day to 2-3 ppm at night. Fish trapped in these areas die, but the entire water body is not affected. Most summer kills occur in the Lower Peninsula.
Spring kill occurs in lakes and streams as water rapidly warms in May and June. This natural mortality rarely kills many fish and typically affects large bluegill, sunfish, crappie and pike, bass, perch, and suckers. Fish are weaker coming out of winter due to feeding less, which coupled with the stress of spawning causes mortalities during times of rapid turnover stirs up bottom water low in O2. Most spring kills likewise occur in the Lower Peninsula.
Saturday is the trout season opener, but one may have to wear their snowshoes, eh?