08-22-2001 Council Agenda - Laserfiche WebLink

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Aug-1T -2001 12:16pm From - MINNESOTA HOUSE OF REPRESENTATIVES 6512064121 Winterklll T -054 P.000 /006 F -131 What is winterkill? The term winterkill refers to the death of fish from low oxygen under ice covered conditions. What causes low oxygen? Most oxygen enters the water by the photosynthesis of green plants or through the water-air interface. Green plants require sunlight to preform photosynthesis. When ice forms, the water -air interface is eliminated and the amount of sunlight reaching the green plants is reduced. When snow covers the ice, the snow blocks out more sunlight. Once sunlight is restricted, green plants can't preform photosynthesis and, as a result, the plants start to die and decompose. The decomposition process uses oxygen. If enough oxygen is used. up by decomposing plant material and fish respiration, fish suffocate. How low does the oxygen level have to go before fish sMoodie? oxygen as the level when some fish arc The D.N.R. generally uses a level of 2 parts per likely to die. Do all the fish die? It's very unusual for all the fish in a lake to die. Are all kinds of fish equally likely to die as a result of winterkill? No. Some kinds of fish are more vulnerable to low oxygen levels than other kinds. Trout are the most sensitive species. Btuegill and bass are also quite vulnerable. Northern pike, walleye and crappie are less vulnerable than bluegill and bass. Bullheads and buffalo are fish most tolerant of low oxygen levels. What kind of lakes are most vulnerable to winterkill. depth of a lake is a better Fertile, shallow lakes are most vulnerable to winterkill. The average dep indicator of vulnerability than maximum depth. Lakes with one deep hole and large areas of shallow water are more vulnerable than lakes with modest average depth The lower the volume of water in the lake, the more vulnerable it could be to winterkill if other considerations are equal. Can anything be done to prevent winterkill? Yes. Two types of aerators are available that can prevent winterkill. The first type uses compressed air bubbled through a tube. This method works by circulating wanner water (39 F.) from the bottom of the lake to the surface and prevents the formation of ice over a good portion of the lake. This allows the green plants to photosynthesize and oxygen levels to stay high enough for the fish to survive. This type of aerator is used every year and has to be started early in the winter before the green plants have started to die and decompose. The second type of aerator is called a pump and baffle aerator_ This type of system operates like a manmade waterfall- A large capacity pump moves water through a "baffle" - a chute with metal plates welded inside - causing lots of splashing. The splashing of large volumes of water increases the amount of water exposed to the air, which allows enough oxygen to dissolve in the water to prevent the fish from dying. This type of system can be started as needed and doesn't have to be used in mild winters. What is done on lakes without aerators? Once the D.N.R. determines that fish. ate likely to die, lakes with public access Can be opened to "Unlimited Fishing". This allows licensed anglers to take unlimited numbers of fish with less restricted methods. By allowing unlimited numbers of fish to be harvested, the D.N.R. hopes to allow licensed angler to use a resource that would otherwise be wasted. These lakes can be restocked with fast growing fish the following spring to provide fishing in future years. Page 39