From the G&F
It is important to note that the Missouri River and Lake Oahe walleye fishery is maintained entirely through natural reproduction. North Dakota Game and Fish has not stocked walleye in its portion of the lake since 1981, and the last time South Dakota stocked walleye in its portion of Oahe was 1998.
Thus, maintaining an adequate number of sexually mature walleye, especially females, is a crucial consideration. It is also important to have an understanding of the species’ reproductive strategy in determining how many females are necessary for maintaining the fishery.
For example, Lake Oahe’s Beaver Bay is an important site for walleye reproduction. In spring 2016, the Department netted, tagged and released 758 mature female walleyes in Beaver Bay. Since a mature female walleye may carry 130,000 eggs, these 758 fish, in all likelihood, deposited close to 100 million eggs in the bay last spring.
Considering these 758 walleye represent only a small portion of fish in Beaver Bay, let alone all of the Missouri River and Lake Oahe, this population has the potential to produce many billions of offspring annually.
The amount of water Mother Nature provides, and how that water is managed by the U.S. Army Corps of Engineers, remains the primary factor governing the quality of this walleye fishery. Floods (1997 and 2011) and droughts (1988-92 and 2001-08) have periodically influenced this walleye fishery by reducing available habitat and causing forage shortages. Conversely, environmental conditions and water level management that favor forage fish production, walleye reproduction, growth and survival, have produced extraordinary results.
This is where the walleye’s reproductive strategy is clearly effective on the Missouri River and Lake Oahe. Walleye are capable of producing many more offspring than are needed so they can quickly increase in numbers when environmental conditions are favorable. Even if environmental conditions are poor, and the number of sexually mature walleyes declines, they still have the ability to rebound quickly. On some occasions, the Missouri River and Lake Oahe have seen walleye reproduction that was too good for the available forage base to support.
Another important biological consideration is maintaining a healthy length and age structure in this population. A healthy walleye population contains many more younger, smaller fish than large, older fish. However, the presence of large, older fish is a good indicator of a healthy population.
Game and Fish netting and electrofishing surveys indicate a balanced walleye population in the Missouri River and Lake Oahe. While small fish are abundant, fish 20 inches and longer are common, and fish living into their teens and measuring longer than 30 inches are sampled annually.
Social Perspective
Would some form of length regulation or more restrictive harvest lead to anglers encountering, but not necessarily harvesting, larger walleye?
Game and Fish has used different length restrictions for walleye fisheries at times, including minimum length limits, maximum or “one-over” length limits, protected slot length limits (no harvest allowed on 15- to 20-inch fish, for example), and reverse slot length limits (harvest only allowed on 15- to 20-inch fish, for example).
After a half-century or more of experimenting with these various regulations on walleye fisheries across North America, biologists have pretty much defined the biological and social conditions that must be present for such regulations to yield positive results. Game and Fish biologists evaluate the utility of each of these regulation types annually to determine if they could help improve the present condition of any given fishery.
More anglers approach Game and Fish with questions regarding a one-over 20-inch length restriction than any other type of regulation. Again, the biological answer is that the Missouri River has plenty of mature female walleyes to maintain this naturally reproducing population. But from a social perspective, would a one-over 20-inch length restriction enable anglers to catch more big fish?
A Game and Fish Department creel survey of Missouri River and Lake Oahe anglers in 2015 provides some insight as to how a one-over 20-inch regulation would influence angler use of these fish.
Creel clerks interviewed 1,126 individual anglers (498 fishing parties) between Garrison Dam and the South Dakota border, and measured the lengths of walleye harvested by anglers whenever possible. Sixty five percent of harvested walleye were between 15 and 20 inches, 34 percent were under 15 inches, and less than 1 percent were 20 inches or longer.
None of the parties interviewed had more than one walleye 20 inches or longer per angler. Thus, a one-over 20-inch regulation would not have prevented the harvest of a single walleye 20 inches or longer among the 1,126 anglers surveyed.
Creel clerks clearly did not interview every single angler who fished the Missouri River or Lake Oahe in 2015. However, the survey information does provide overwhelming confidence that a one-over 20-inch regulation would have virtually no impact on this walleye fishery.
Moving Forward
Currently, the five-walleye daily limit, with no length restrictions, is maintaining a biologically healthy walleye population in the Missouri River and Lake Oahe. More restrictive harvest regulations at this time are biologically unnecessary, and would not likely lead anglers to catch more large walleye. Needlessly complicating regulations, without benefiting the fishery or anglers, is not the North Dakota Game and Fish Department’s philosophy.
However, that doesn’t mean the current situation will last forever, and Game and Fish biologists will continue to monitor and study this walleye population, and the anglers who use it, to ensure that effective harvest regulations are in place for maintaining the highest quality fishing possible for years to come.