MN DNR Lakefinder – How to Interperet Trap Net Numbers

When looking at the lakefinder surveys ive always focused on category which lists the Length of Select Species Sampled count to determine if the lake has good numbers of fish. To be truthful ive never really understood how to make sense of the data presented in the section showing the trap and gill net numbers. Can someone explain to me how you look at that data and make sense of it? I feel like im missing out on some important information by not understanding that section.

Each sample method will yield different results in regards to the size of fish they catch.
I haven’t looked at that info in a while, since moving to the river, but i believe if you look at the results of each side by side you’ll see a difference in size class captured.

I’m sure someone will chime in with a much better answer!
Good question.

I used to work for the DNR and assisted with some sampling at times.

Certain types of sampling don’t work well to determine what species may be doing well in a certain lake. For example, sampling nets don’t work hardly at all to determine a population of bass, especially largemouth. They often inhabit shallow weedy cover and nets are almost never placed there. Electro-sampling works far better. A standard sampling net works pretty good to get a good estimate for walleyes. They’re usually left out in shallower water at night because that is when walleyes are present in those areas. They are hit or miss for panfish populations.

Also note that lakes are surveyed every few years. They are not usually done every year or even every other year because there simply isn’t enough manpower or funding. Big, heavily pressured, and well-regulated lakes are often done more often (Mille Lacs comes to mind). It will list the month and year of the most recent population survey on their website.

If you’re looking for a specific species of fish in a specific size range because you intend to harvest some, you should be looking for that on their size range chart. For example, if you don’t see any crappies sampled in the 12-14 inch range, there’s probably not many in there. Doesn’t mean there aren’t ANY, but a sampling study usually reveals at least some.

Certain lakes also inhibit a faster growth rate than others because they are more fertile and/or have a better base of forage. Perch are generally a good prey item for most gamefish species so if there is a good perch population, there’s a better chance for quality gamefish.

Lastly, be sure to look at the secchi disk reading. This indicates how clear the water is. Water clarity can obviously change based on local conditions (rain, runoff, etc) but as a general rule, the clearer the water, the deeper the fish will be.

Hope that helps.

gimruis wrote:

I used to work for the DNR and assisted with some sampling at times.

Certain types of sampling don’t work well to determine what species may be doing well in a certain lake. For example, sampling nets don’t work hardly at all to determine a population of bass, especially largemouth. They often inhabit shallow weedy cover and nets are almost never placed there. Electro-sampling works far better. A standard sampling net works pretty good to get a good estimate for walleyes. They’re usually left out in shallower water at night because that is when walleyes are present in those areas. They are hit or miss for panfish populations.

Also note that lakes are surveyed every few years. They are not usually done every year or even every other year because there simply isn’t enough manpower or funding. Big, heavily pressured, and well-regulated lakes are often done more often (Mille Lacs comes to mind). It will list the month and year of the most recent population survey on their website.

If you’re looking for a specific species of fish in a specific size range because you intend to harvest some, you should be looking for that on their size range chart. For example, if you don’t see any crappies sampled in the 12-14 inch range, there’s probably not many in there. Doesn’t mean there aren’t ANY, but a sampling study usually reveals at least some.

Certain lakes also inhibit a faster growth rate than others because they are more fertile and/or have a better base of forage. Perch are generally a good prey item for most gamefish species so if there is a good <strong class=”ido-tag-strong”>perch population, there’s a better chance for quality gamefish.

Lastly, be sure to look at the secchi disk reading. This indicates how clear the water is. Water clarity can obviously change based on local conditions (rain, runoff, etc) but as a general rule, the clearer the water, the deeper the fish will be.

Hope that helps.

that’s awesome info……..except…… where you say there sampled every other year. the lakes I look at are sometimes 10 to 15 years part. more specific are lakes up in Itasca county.

glenn57 wrote:

that’s awesome info……..except…… devil where you say there sampled every other year. the lakes I look at are sometimes 10 to 15 years part. more specific are lakes up in Itasca county.

Ya you’re right, it could be years in between surveys which would make the information posted even less reliable.

how do you interpret the CPUE column and the normal range next to it?

CPUE is catch per unit effort. Its basically an indicator of the abundance of that specific species.

Focus more on the fish size structure sampled. The CPUE is almost always going to indicate a higher density of more common fish like a rough fish such as bullheads or a common panfish like bluegills.

Here is an article I found on the subject.

There’s a particular person I know who likes to travel to new areas, select to fish lakes he’s never fished before, and catch that lake’s walleyes. He also tracks religiously the surveys the DNR conducts regularly on most of Minnesota’s lakes – in particular, the gill-net catch rates of walleyes in waters he might potentially fish.

That’s not an illogical place for such research to begin. Why fish for walleyes in a lake where there’s no evidence they exist?

That said, most fish managers will tell you that gill-net catches from lake surveys should be just part of the equation, that other factors may dictate actual fishing success – among them, it should be noted, the skill of the fisherman or woman.

Here are a few examples of recent gill-net catch rates from popular lakes in Minnesota:
Lake County Acres Catch Year
Lake Sarah Murray 1,200 45.5 2010
Green Lake Kandiyohi 5,560 10.1 2012
Lake Waconia Carver 3,080 4.1 2012
Lake Osakis Todd 6,390 7.0 2010
Height of Land Becker 3,790 2.6 2010
Otter Tail Lake Otter Tail 13,725 12.2 2013
North Long Lake Crow Wing 6,140 4.5 2012
Leech Lake Cass 110,300 9.4 2012
Lake Vermillion St. Loius 39,270 15.4 2012
Upper Red Lake Beltrami 48,000 52.1 2013
“Every lake nets differently,” says Henry Drewes, DNR regional fisheries manager in Bemidji. “Most valuable are trends through a given time on a particular lake.”

Other considerations, Drewes says, include available prey for walleyes, the makeup of the lake in terms of size and depth and shape, the complexity or simplicity of the overall fish community, the lake’s vegetation and fertility, and more.

In other words, dig deeper into that lake survey than just the gill-net catch of walleyes.

There are some general guidelines the angler could use, he adds. For example, “If the gill-net catch rate is three or less, regardless of where you’re at in the state, it’s a fairly low abundance of walleyes. But that doesn’t mean you couldn’t have good fishing at some point in the year.”

Between three and eight walleyes per net indicates a “moderate” population, in general, he adds. If the gill-net catch rate is greater than eight, the walleyes are fairly abundant.

After making that determination, Drewes says, the angler must investigate specifics of a lake. Even within the same area of the state, walleye catch rates can vary dramatically. Drewes says he’s seen instances of 100 walleyes per gill net.

That said, impressive numbers don’t always translate to impressive catches.

“When they see high (catch rates), people like to think it’s a lights-out success lake,” he said. “That’s not always the case, either. You need to be cautious not to read too much into the net-catch number.”

There also are times when low net catches of walleyes likely aren’t indicative of the actual population. Two lakes in the Little Falls area, for example, tend to produce low gill-net catches, but produce good returns via other sampling methods, according to Eric Altena, DNR area fisheries supervisor in that area.

Sullivan Lake is one of them. There, the walleye gill-net catch typically is a one or two fish per net, Altena says. On the other hand, ice-out trap nets and electrofishing assessments indicate an impressive population. As do anecdotal reports from anglers.

The lesson: Don’t make assumptions.

“The best thing to do is talk to area (DNR) staff,” Altena said, adding that some inside insight often is valuable information for a walleye angler who’s a first-timer to a particular water.

Those fine guys and gals at bait shops, too, can validate or discount gill-net catch rates.

Dean Paron, DNR fisheries supervisor in Finland, said some lakes just “net better” than others. It’s also important to consider lake “class,” a system based on the research paper, “An Ecological Classification of Minnesota Lake with Associated Fish Communities,” produced by the DNR’s Dennis Schupp in 1992. It’s used now to determine how a lake and its fish perform compared with similar counterparts. Classification is based on various criteria.

Trap nets collect walleyes during DNR lake surveys, but it’s the gill nets that more precisely measure the density of walleyes in a lake. That’s because those nets are more closely associated with walleye behavior, said Melissa Drake, DNR fisheries research and policy manager. Gill nets are set nearer walleye habitat, “where they’re traveling,” she said.

To further improve consistency, surveys are conducted at the same time of year, and nets are set at the same locations during each lake survey, Drewes said.

He suggests anglers visit “lakefinder” on the DNR’s website. That’s where they’ll find links to lake surveys.

“It’s a starting point, then you build on that starting point,” he said.

Categories: Feature, News, Social Media, Walleye

Jeez John, you really got into this THICK didn’t you. Pretty good information, if your target is walleye of course.

Yeah I guess I did. SLOW at work today and my love for Walleye’s is strong.

Thanks everyone! Lots of stuff to absorb here. Surely understand the fish surveys are just one piece to the puzzle. Part of the fun of the hunt

Gimruis, thanks for the info on your experiences.

To the OP, I use these surveys and Lakefinder A LOT. Whenever I’m looking for new lakes to fish it’s the first place I start. As Gimruis said, look at the size chart. If I see big numbers of small undesirable sizes and low numbers of larger fish I wont fish those unless I find another source telling me otherwise. However if I see more level size structure numbers I will put a pin on that lake in my phone map as a lake to check out. Keep in mind it’s all relative and it the time of year, type of trap/net, location of traps, etc all can effect the numbers.

I use the # and size part of Lake finder a lot. It helps to determine if a lake is a good #’s lake or a Good fish size lake. Seems like often they are one or the other. Sometimes based on the # of years ago the sample was done you have to try and adjust the size for growth. It does seem like the span between testing is getting larger than it use to be. I’m sure funding has plenty to do with that. Often if I’m looking for a new lake to try, The lakefinder is the 1st place I go – Followed by my lakemaster app. to see if it has the type of structure I like to fish.