Over the years, North Dakota Game and Fish has developed a body of fishing regulations based on sound fisheries biology and management practices. A general rule of thumb is that if a regulation isn’t going to help the resource, then don’t put it in place, and conversely, if a regulation is no longer serving its intended purpose, it should be taken off the books.

Those principles are part of the reason why North Dakota has only a few waters that have some type of fish size restriction. For every 14-inch minimum walleye rule, the regulations become a little less angler-friendly. To justify the inconvenience to anglers, Game and Fish biologists have to have reasonable expectation of benefits.

Fish size limits have several forms. Each can produce results but only under the right conditions. In essence, if a specific water has “x” conditions, then the rule may help. Without meeting those conditions the regulation will not help, and in some cases could actually hurt the fishery.

Here’s a look at the different types of size limits and the conditions under which they could prove beneficial.

Minimum size limits
Minimum size limits are designed to reduce harvest of small fish, allowing more fish to reach a desirable size. A minimum size limit works when there is high angling mortality, when natural mortality is low, when reproduction is low, and when growth is relatively good.

Many anglers will recall a 14-inch minimum walleye size restriction on Lake Sakakawea that started in 1991. This was put in place to protect a couple of strong year-classes of stocked fish that had not yet reached 14 inches. At the time, Sakakawea was at a low level and had not had natural walleye reproduction for several years, and the walleye population was heavily skewed toward smaller fish. Without a regulation, biologists felt there would be high angler harvest on these 12-13-inch fish, because the lake didn’t have many other walleyes to spread out the catch.

Over time, those small walleyes grew up, water returned to Sakakawea, the walleye population balanced out and the 14-inch minimum was removed in 1998.

Slot limits
Slot limits are designed to increase the number of larger walleye by protecting mid-sized fish. An example of a slot limit would be a requirement that anglers release all walleyes from, say, 18-23 inches in length.

For a slot limit to be effective, the population should exhibit high reproduction, slow growth (especially for smaller fish), high natural mortality, and high angling effort.

The other side of slot limits is that they are usually not popular because anglers must release nice-sized walleye they are accustomed to keeping. There is also little documented evidence that slot limits work.

Maximum size limit
A maximum size limit requires release of all fish longer than a certain length. This regulation is designed to reduce the harvest of large fish, and is effective when there is high angling mortality on large fish, and natural reproduction is limited by the lack of large fish.

A derivative of the maximum size limit is the “one-over” regulation. This restriction allows harvest of one fish longer than the specified length. In North Dakota, a one-over 24 inches regulation is in place for catfish on the Red River System. This rule effectively allows limited harvest of large catfish while preventing overharvest of mature fish.

The state also had a one-over 18 inches regulation for walleyes on Lake Oahe and the Missouri River south of Garrison Dam, starting in 1999. At the time, because of a smelt population crash in Lake Oahe, walleye growth rates were very low. The regulation was put in place to protect large, mature walleyes, while encouraging harvest of smaller fish, which at the time were plentiful.

This regulation was eliminated in 2002, when it was no longer needed.

Before you push for special regulations on your favorite fishing hole, take a minute and realize a special set of circumstances must be weighed before Game and Fish will consider new lake regulations.

The bottom line is regulations which will not help, enhance or improve a fishery, while these may serve as a warm and fuzzy feel good for anglers, add needless confusion to fishing rules.

Doug Leier is a biologist for the Game and Fish Department. He can be reached by email:dleier@nd.gov