DeWitt is a Department of Natural Resources Fisheries Division technician at the Alpena research station.
Over the coming winter, he'll examine approximately 1,500 walleye that were caught, frozen, and shipped to his office by fellow DNR field workers throughout the state.
His review will determine what percentage of the walleye living in certain Michigan waters were produced in Michigan fish hatcheries and how many were wild fish.
While the DNR's six hatcheries are best known for salmon and trout production, but the leading species - by the numbers - planted by the DNR is walleye.
Michigan began its walleye program in the late 1970s, as the fish began gaining popularity among anglers. Today, walleye rank among Michigan's top three angling opportunities, with bass and salmon.
"We produce approximately 5 to 10 million walleye fingerlings each year, on average," said DNR Hatcheries Manager Gary Whelan. "We also produce nearly 20-30 million fry, smaller fish that measure about one-third-inch.
"But what's really amazing about Michigan's walleye program is how little of it can be accomplished in the controlled conditions of the hatchery. All the fingerlings are produced in outdoor rearing ponds, and those ponds depend on weather conditions."
Sometime around early April each year, fisheries managers collect and fertilize eggs from spawning walleye in the Tittabawassee River in Midland, the Muskegon River in Muskegon, and Little Bay De Noc near Escanaba.
One large adult female walleye produces approximately 100,000 to 300,000 eggs. Each female is fertilized with one male to maximize genetic diversity. The fish are collected by electro-fishing or in nets, handled carefully and released after the collection.
The Lower Peninsula eggs are sent to the Wolf Lake Fish Hatchery near Kalamazoo, and Upper Peninsula eggs go to Thompson State Fish Hatchery. They incubate for 18-21 days before hatching.
Unlike salmon, walleye do not spend much time at the state hatcheries. Within the first five days of their lives, they are placed in a solution of tetracycline, which imprints a permanent chemical "mark" in their bones. The stain does not harm the fish, but is visible under a black light, which scientists use to identify them as hatchery fish. After the tetracycline bath, the walleye are transferred to one of nearly 50 outdoor ponds located throughout the state.
Many of the rearing ponds are owned by private groups, working in partnership with the DNR to promote walleye production in Michigan. In early spring prior to the arrival of the walleye hatchlings, specialists and cooperators are filling and fertilizing the ponds with either inorganic or organic fertilizers.
"Young walleye feed on zooplankton," said DNR Fisheries Biologist Jim Baker, a unit supervisor whose district includes southern Lake Huron. "To get zooplankton growing, we put soybean meal in the ponds several weeks before the fish arrive. The part of the equation we can't control is air temperature and sunlight, which are critical to producing a good crop of zooplankton."
By the second week of June, fish in the Lower Peninsula ponds have been there for approximately 50 days, and are 1.5 inches on average. The same process takes until mid-July in the Upper Peninsula. A sample of the fish are tested to ensure they are healthy, and they are then ready to go to their permanent homes on rivers, inland lakes and the Great Lakes.
But how do DNR managers decide where to stock walleye?
"We base our stocking decisions on three goals," said Lake Huron Basin Coordinator Tammy Newcomb. "In some places, we stock walleye in an effort to restore lost populations or to rehabilitate degraded populations. In other places, we stock to provide an additional recreational opportunity. Sometimes, we use walleye to improve an existing fishery. Predation by walleye on stunted bluegill and perch populations can improve those fisheries."
On inland lakes in the west and southwest part of the state, DNR biologist Jay Wesley said he looks for at least 80 acres with a fair amount of sand, few weeds, and shoals with depths of 5-20 feet. Lakes with a good forage base of minnows or stunted panfish also are desirable.
"Turbid water, particularly in warmer river systems, seems to provide optimal habitat," Wesley said. "They don't like muck bottom lakes, where you typically find largemouth bass, bluegill, crappie, and pike."
He said the DNR typically will plant a lake three times, and perform follow-up net surveys to determine whether the species is successfully adapting. In most Michigan waters, it takes three to five growing seasons for inland lake walleyes to reach 15 inches, the minimum size to keep on inland waters.
Saginaw Bay is perhaps Michigan's best example of the DNR working to rehabilitate walleye through stocking. Walleye once were abundant in the bay, but pollution and over-fishing through the early 1900s, coupled with an influx of exotic species like alewives and rainbow smelt, caused walleye populations to crash by the late 1940s.
The first glimmer of hope came in the late 1970s with the emergence of the DNR walleye program and the implementation of the federal Clean Water Act, which provided large amounts of restored habitat for walleye and other coolwater species.
"I remember when those fish showed up to spawn for the first time in 1981," Baker said. "We've continued an extensive stocking program and fishery has grown and developed into a world-class fishery. Growth rates in Saginaw Bay are 135% of the state average, and the average walleye is 4-5 pounds."