Should Fish Length Limits Be Introduced in North Dakota?

July 8, 2015 by  

Throughout the last 20-plus years, since the drought-busting summer of 1993, many fishing waters in North Dakota have had fish populations that peaked, declined and then peaked even higher.

150708measuring walleye length

Length limits can harm a fish population, and needlessly restrict angler opportunity if the regulation is inappropriate for the fishery

Within that same time period, State Game and Fish Department biologists have had many discussions internally, and with concerned anglers, about whether some type of “length restriction” on certain species on specific waters would serve to preserve fish populations better than existing regulations.

Primarily, the discussions have involved walleye within the Missouri River System or Devils Lake, and recently the emphasis is leaning toward Devils Lake.

With that in mind, northeast fisheries supervisor Randy Hiltner, and fisheries biologist Todd Caspers, addressed the Devils Lake situation in the May issue of North Dakota Outdoors magazine.

The authors, who work at the Game and Fish district office at Devils Lake, state that anglers often express their concern when they believe their peers are keeping too many small or big fish. They believe think a length limit will solve a problem, which is sometimes correct.

On the other hand, length limits can harm a fish population, and needlessly restrict angler opportunity if the regulation is inappropriate for the fishery.

Here’s some of the criteria that biologists use in determining whether length limits are a good fit for the current walleye population at Devils Lake.

 

Minimum length limits are likely to benefit fisheries that meet all of the following:

  • Low reproductive or stocking success.
  • Good growth.
  • Low natural mortality.
  • High angling mortality (fish dying from harvest or after release).

 

Currently, the Devils Lake walleye population does not meet many of the criteria necessary to benefit from a minimum length limit.

In 2008, walleye growth was similar to the North American average, but in 2014, growth was slower. Additionally, with high numbers of 10- to 15-inch walleye in the lake, a minimum length limit would needlessly restrict harvest opportunities for anglers, and could further decrease growth due to increased competition if some fish were protected by a minimum size limit.

 

Maximum length and “one-over” limits (one fish longer than 20 inches, for example) are likely to benefit fisheries that meet all of the following criteria:

  • Reproduction is limited by the number of adult fish.
  • High angling mortality of large fish.

 

Today, Devils Lake’s walleye population does not meet any of the criteria necessary to see a benefit from a maximum length limit.

Large walleye hatches of late indicate that current regulations are maintaining sufficient numbers of adults in the lake. Three of the four largest hatches, in fact, have been produced since 2008. While the percentage of adults longer than 15 inches in 2012 was relatively low at 24 percent, that same year the second largest walleye hatch ever was recorded, indicating there are ample adults in the lake to produce a good hatch if conditions are favorable.

 

Harvest slot length limit:

  • Must meet all of the requirements for a minimum length limit and a maximum length limit, since they are basically a combination of the two.

Protected slot length limits are likely to benefit fisheries that meet all of the following criteria:

  • Good natural reproduction.
  • Slow growth, especially for small fish.
  • High natural mortality of small fish.
  • High angling effort.

 

The article concludes that the current Devils Lake walleye population is not really suited to any of the length limits, but may be close to meeting the criteria for a slot length limit. Game and Fish biologists will continue to monitor the fishery, so that if things change, they can implement regulations necessary to protect this valuable resource.

 


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