OUTDOOR CORNER: FROZEN PONDS DO NOT ALWAYS BRING OUT THE ICY FINGERS OF DEATH

Winter's ill effects become quite apparent to us as it plays havoc with our health, but less obvious is its influence on fish and how it may lead to a fish kill.

The artic cold snap that occurred last week prompted a lot of phone calls to our office concerning potential fish kills in area ponds and lakes. People would ask me, "Will my fish survive this cold weather?" or Will my fish die if my pond is frozen for a long period of time?" The answer to these questions depends on the type of pond

Winter fish kills are primarily caused by low concentrations of dissolved oxygen found in water. Larger fish of any species are usually the first to die when oxygen concentrations become too low. Fish species, such as largemouth bass, bluegill and crappie are more susceptible to low oxygen levels than channel catfish, bullheads or carp.

Luckily, cold water contains more dissolved oxygen than does warm water. Plus, fish are less active during the winter months so they will use less oxygen, thus reducing the chances of having a fish kill.

Winter fish kill do not commonly occur in all ponds, especially ponds found in southeast Missouri. Shallow, fertile, weedy ponds are usually susceptible to a winter fish kill. The production of oxygen depends upon sunlight reaching tiny plants (phytoplankton) in the water.

Sunlight will penetrate several inches of clear ice, but it takes only a small amount of snow to block out nearly all light. Thus, snow causes tiny plants and other submerged vegetation to stop releasing oxygen into the water. Also, without sunlight for prolonged periods of time, the plants may die. As the plants die, the decaying process may reduce the oxygen supply to such a low level that the fish may die.

Landowners can lessen their odds of having a fish kill with good pond management. During the summer and fall, prepare your pond for the winter by keeping the amount of vegetation down to a desirable level. For most fishing ponds, I recommend only 15 to 20 percent of the surface area be covered with aquatic vegetation.

Keep the ice free of snow cover so that sunlight can penetrate the ice. After two to three weeks of snow cover, make "windows" for light to enter by shoveling or sweeping the snow off the surface. These "windows" should be at least 10 feet square and the more of them the better. Before venturing out on the ice, use extreme caution and check its thickness. As a general rule, four inches of ice is sufficient to support even the largest individual. Chopping holes in the ice may seem practical, but water takes up oxygen so slowly for the air that this is of little help.

Shallow ponds should be deepened to at least eight feet. If your ponds is less than eight feet deep and vegetation covers over 20 percent of the pond, try to keep as much of the pond free from ice as possible. A fountain type aeration system or a paddle wheel can be used to agitate the water and keep it from freezing.

In summary, if your pond is at least eight feet deep, aquatic vegetation covers less than 20 percent of your pond, and snow coverage melts within two weeks, then your chances of having a winter fish kill will be low. For more information on preventing winter fish kills, contact the Missouri Department of Conservation in Cape Girardeau at (573)290-5730.

Brad Pobst is a Missouri Conservation Biologist in Cape Girardeau County.