Fisheries managers often hear from anglers who fish in, say, Minnesota and elsewhere, and wonder why specific regulations are applied in those states but not North Dakota.

One of the more frequent conversations involves slot limits.

North Dakota doesn’t have any slot-limit regulations, and most fisheries managers will tell you that a slot limit is likely the most misunderstood of fish size restrictions.

Most anglers refer to a slot limit as a harvestable size range – say, from 14 inches to 20 inches.

What fisheries biologists more often refer to as a slot limit is a “protected slot,” in which anglers must release fish within the slot range, and harvest is limited to smaller and larger fish. Since protected slots typically prohibit anglers from keeping fish of sizes they most prefer, such regulations are probably the least popular of all.

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However, in some waters they are beneficial.

Imagine a walleye population that experiences consistent reproductive or stocking success but has limited food resources, so the abundant small fish don’t grow very fast. Now throw in a lot of angling pressure, and the few fish that do reach a size large enough to harvest are quickly cropped off, with few fish making it to larger sizes.

A protected slot limit is designed to alleviate some of that and produce a more balanced size structure in a couple of ways. First, since anglers can’t harvest mid-sized fish, they would be more likely to harvest smaller fish, in turn thinning the density of small fish and increasing the growth rate of remaining fish. Then, as those fish are growing faster, they are protected from harvest when mid-sized, allowing them to reach longer lengths.

In North Dakota, because Lake Sakakawea’s walleye population is strong and has a desirable mix of walleye sizes, a protected slot limit is not warranted.

On Lake Oahe and the Garrison Reach of the Missouri River, the walleye population includes abundant small fish, and growth has slowed while mortality has increased. However, a more restrictive regulation would not address underlying forage problems impacting the fishery. A slot limit would needlessly restrict harvest, and possibly create more problems by increasing the walleye population density, thereby increasing competition for food at a time when forage is extremely limited.

On Devils Lake, fishing effort is high, at times, but Game and Fish Department studies indicate harvest and mortality rates from fishing are not extreme, and natural mortality is likewise moderate. Applying a slot limit to this population is not biologically necessary, but Game and Fish biologists continue to evaluate the walleye fishery to determine if special regulations are at some point necessary.

The discussion on fish management from state to state, and even from lake to lake, is as diverse and dynamic as the technology employed by anglers. The discussion topics may change, but the passion of anglers will remain, which is a good thing.

Leier is an outreach biologist for the North Dakota Game and Fish Department. Reach him at

Doug Leier
Doug Leier