There are many things to think about while anticipating the coming of the “big blizzard,” but the National Weather Service has come up with another one. It seems that they have been naming winter storms (mostly when they affect the Eastern states) which tells me that they have too much time on their hands. As I patiently await the onset of the blizzard I am trying to think of a fitting name for it. A few of the names that come to mind are Ole, Sven and Lars and, for the sake of gender equity, Lena and Olga could be thrown into the mix. Looking back a few years (quite a few) to when I was in school, it seems like there were a lot more winter storms but there were less school closings. I can remember listening to the radio and hearing that school was still on and buses would be running on plowed roads only. I can also never recall closings being announced a day ahead of time, but the media services we have available today make that information more readily available. I don’t think folks today suffer from “chicken little” syndrome, but with that information they are just more cautious.
The DNR has issued the following news release pertaining to winter kill which may be of interest to many area fishermen.
Cold weather causing winterkill on some southern Minnesota lakes
An especially cold winter is showing its effects around some southern Minnesota shallow lakes and ponds with dead or dying fish. In most cases it is the result of a normal process known as “winterkill,” according to the Minnesota Department of Natural Resources. Shallow lakes in southern Minnesota with an average depth of less than six feet are most susceptible.
Winterkill conditions are created when sunlight is unable to penetrate the ice, and oxygen levels in the water drop, said Craig Soupir, Waterville area fisheries supervisor. Fish may be unable to survive in these low oxygen conditions. “Lack of sunlight limits oxygen production in some aquatic plants and at the same time, decomposing aquatic plant matter causes a drop in oxygen,” Soupir said. “When this process occurs under ice cover it can cause fish to become stressed and, if severe enough, to suffocate.”
Winterkill is a natural process that can actually benefit a lake. In lakes with high numbers of carp, for example, periodic winterkill can thin out their numbers and create a void in the fish community. This void is often is followed by improved water clarity, increased aquatic vegetation and a re-introduction of native game fish species.
Soupir said populations of game fish can sometimes rebound quite dramatically in years following winterkill. Increased production from existing fish, rapid growth of stocked fish and improved survival of young fish can all contribute to a lake that can quickly become productive to anglers.
It is not unusual for lakes in Southern Minnesota to experience some winterkill on an annual basis. However, the severity of winterkill varies greatly depending on factors such as snow depth and length of time snow covers the ice, lake depths, water inflows and the rate at which oxygen drops over time. Most often, winterkill events on these shallow basins are partial and rarely do all fish in a lake die.
“Fish can become trapped in an area of the lake with low oxygen, causing a partial winterkill,” Soupir said. “This doesn’t mean the entire lake has winterkilled.” Many times, schools of fish find refuge in other areas of a lake with sufficient oxygen levels to survive. Just because one part of a lake shows signs of winterkill, does not automatically mean the entire lake has winterkilled.
The fishery in some lakes known as “boom and bust” lakes is specifically managed around winterkill. These shallow lakes typically have high survival rates of stocked fish, which grow rapidly and provide quick turnaround for anglers. These lakes rely on frequent winterkills, which may happen every four or five, years, to reset the lake and allow the fish population to achieve its boom times of quality-sized fish.
While some larger and deeper lakes in southern Minnesota have installed aeration systems to reduce the probability of winterkill effects, aerated lakes are still susceptible to winterkill. Attempts to aerate very shallow lakes often do not work well for maintaining a fishery.
Some species of fish are more vulnerable to winterkill than others, Soupir said. Trout require the most oxygen and start to stress at oxygen levels below 5.0 parts per million (ppm). Bluegill and largemouth bass are moderately sensitive to lower oxygen levels. Walleye, yellow perch, northern pike, carp and crappie species have intermediate tolerances and have been shown to survive winters with oxygen levels down to about 1.0 ppm for long periods of time. Bullheads and fathead minnows are the most tolerant of low oxygen and are the last to survive.
“We don’t usually see winterkill until oxygen levels fall well below 1.0 ppm for several days throughout a lake,” Soupir said.
He added that in the late winter, species such as northern pike have a tendency to seek open water areas as an impulse to their early migratory spawning run to shallow water or flooded inlets.
Anyone observing dead or struggling fish should report their findings to the local DNR fisheries office. Note the species and approximate numbers and sizes of each kind of fish. The information will help the DNR identify which lakes experienced winterkill and the extent in conjunction with ice-out netting assessments and observations. Follow-up stocking of fish may ensue, if consistent with DNR lake-specific management plans.
For more information, contact a DNR area fisheries office.
Until next time, stay warm and get out when you can and enjoy a little Minnesota winter fun.
Please remember to keep our troops in your thoughts and prayers because they are the reason that we are able to enjoy all the freedoms that we have today.