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Scott Rall: What it takes to grow a walleye

Scott RallDaily Globe outdoors columnist EDITOR'S NOTE: This is a two-part series about walleye stocking in southwest Minnesota -- how it is done and what is happening now that is different than anything that has happened here in the past 25 year...

Scott Rall
Daily Globe outdoors columnist 

EDITOR’S NOTE: This is a two-part series about walleye stocking in southwest Minnesota - how it is done and what is happening now that is different than anything that has happened here in the past 25 years.

Sometimes it takes decades for a story to come full circle, and this is one of those stories. I will start with a little background. I am friends with and a registered volunteer of the Minnesota Department of Natural Resources. I have volunteered with almost every department they have. I have worked in the Wildlife Division, the Enforcement Division and in the
Fisheries Department. I used to work with what was called the Trails and Waterways Division but it is now called the Department of Ecological Services.
I got a call from the area fisheries supervisor in Windom, Ryan Doorenbos, and he was telling me about some work they were doing on Lake Sarah in Murray County, and thought I might be in interested in tagging along to see the work they were doing. I met them on Saturday a few weeks back and jumped into their boat for a day’s worth of observing.
The work they are doing is in the area of natural walleye reproduction. In southwest Minnesota we have many prairie lakes. A prairie lake is one that is most identified with stained water and shallow depths. These lakes were not always shallow. In a study they did in Lake Okabena years ago, they determined that the lake used to be 23 feet deep. Today it is about seven feet deep, and this is from the deposit of sediment over decades.
All prairie lakes have had some amount of natural sedimentation even before man showed up. The rate of sedimentation, dirt moving off the land and into the bottom of the lake, increased dramatically when row crop production became the norm. Over the past 30 years a lot has been done by producers to keep the dirt where it belongs and not in the bottom of the lake.
Sedimentation continues today but at a much slower rate due to the implementation of Best Management Practices by farmers and the work being done by the different watersheds boards across the state.
The average prairie lake in southwest Minnesota gets stocked about two out of every three years. This is not because the walleyes in these lakes don’t spawn; it is because they don’t spawn successfully.
There are many factors that play a part in successful spawning. Proper egg development, being fertilized at exactly the right time, proper in-lake habitat and having the water temperatures line up all have a role to play in successful spawning.
In a Canadian shield lake with little to no sedimentation the walleye will find a wind-driven shore where the bottom is made up of rock rubble/gravel bottom. When the water temperatures get to 45-50 degrees the male walleyes will move to the shallows and wait for females to follow them. Males pretty much hang out in the shallows waiting for the ladies to show up when they are ready.
Typically the females will only be in the shallow water for a very short time. Once they deposit their eggs the males only have less than a minute to fertilize them. If this does not happen in this very short window, the eggs will never turn into a walleye. Toward the tail end of the spawn, both males and females will move back to deeper water.
The eggs settle down into the nook and crannies of the rocks where they are safe from being eaten by other fish. The windswept shores then provide a continual supply of highly oxygenated water passing over the top. When the eggs hatch they can still hide in the substrate until they move out on their own.
Very few of the eggs actually make it to adulthood but one walleye can lay thousands of eggs. I think the survival rate to adulthood is about 3 percent under normal conditions.
Many lakes in Minnesota that have the necessary underwater habitat never need stocking. Nature does it by itself and this would be the annual events in fish reproduction in a perfect world.
Fast forward to southwest Minnesota. Walleyes are stocked, and when the females get to the age of 2 to 3 they become fertile and can try their instincts at reproduction. Males mature faster and can participate at a little over the age of 1.
So the female lays her eggs near the shore in a mud bottom. The male fertilizes the eggs and the spawning fish move deeper.
What happens next? Every bullhead in the lake will move in and start eating the eggs. Every other fish, for that matter, will do the same thing. Crappies, perch, bluegills and catfish will all take part in the smorgasbord that is walleye spawning in a prairie lake.
There are no nooks and crannies for the eggs to find shelter in. Eggs are laid and fertilized but very, very few ever hatch due to predation.
Another issue in prairie lakes is that when the wind blows it stirs up the mud, and when the mud settles back it does so on the eggs laid in the mud, and they suffocate and never hatch. Even if they survive not getting eaten they can still die for many other causes. Water temperature can also kill unhatched eggs and fry. Fry is a newly-hatched egg and really does not look a whole lot like a fish.
If the eggs are laid and then a super cold span develops and the water temperatures drop, these eggs and fry can still die. This is the reason some year classes (eggs all laid in the same year) never materialize. The lake will then have a bunch of 15-inch walleyes and a bunch of 6-inch walleyes and no walleyes of the sizes in between.
That year class just failed for one reason or another. In some cases the walleyes might be just ready to spawn and the weather gets really cold. If too many days elapse before the water warms back up the female walleye will not spawn at all and will just reabsorb their eggs as if it never happened. They will then wait until next year to try again.
This is why lakes are stocked at lower rates and more often than larger stockings on great intervals. This helps even-out the year classes and make for a fish population that is well-rounded with some fish of every size.
Stocking rates are determined by a population assessment that is done by the DNR on regular intervals. They can use historical data to determine how many fish are in the lake compared to past assessments. Stocking rates go up when fish numbers decline and stocking rates go down when fish numbers are higher. This effort is designed to give every lake a balance.
A lake can actually get overstocked to a point where there is not enough for the fish to eat. When this happens, fish grow very slowly and stocking is normally eliminated or dramatically reduced until the situation corrects itself.
Next week I am going to tell you about two lakes in the area that have not been stocked since 1991, and they are two of the best lakes in the area. I will explain what the DNR Fisheries staff is doing to try to make every lake like these two special bodies of water. You will also see my explanation of how this story took 20 years to complete.

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