Surveys shed light on Devils Lake fish populations
Walleyes had a decent hatch this year on Devils Lake, but the number of "keeper"-size fish in the 15- to 20-inch range is slightly below average, results from two separate fish population surveys show.
At the same time, overall walleye abundance in Devils Lake is slightly above average, said Todd Caspers, district fisheries biologist for the North Dakota Game and Fish Department in Devils Lake.
"The only fish size slightly below average right now is kind of those 15- to 20-inch" walleyes, Caspers said. That's likely the result of three weak year-classes in 2013, 2014 and 2015 that now would have been in that keeper-size range, he said.
A variety of factors, including forage and spring weather, can influence the strength of a year-class—fish recruited to the population from a particular year's hatch—Caspers said. Game and Fish offset the lower production by stocking more than 1.7 million walleye fingerlings in 2016 and 1.4 million fingerlings in 2017.
The department didn't stock any walleyes this year in Devils Lake.
"It's not like there's no keeper walleyes out there," Caspers said. "It's just that they're a little less abundant than people are used to."
Game and Fish conducts the adult fish population survey every year in early to mid-July, Caspers said, setting nets in 39 locations across the lake and leaving them overnight. Crews follow that up with a survey in mid-September, setting smaller-mesh nets at the same sites to sample for young-of-the-year fish.
Game and Fish set 38 nets for the September fall reproduction survey instead of the normal 39 because of lower water levels and hazardous conditions that prevented setting a net in the north end of Pelican Lake, Caspers said.
Mirroring what many anglers saw this summer, walleyes in the 10- to 15-inch range were the most abundant in the adult fish survey, with about 9.6 per net, Caspers said, up slightly from the average of 9 per net.
Overall walleye numbers were at 22.2 per net, up slightly from the average of about 20.5, he said.
Crews sampled about 4.3 walleyes per net in the 15- to 20-inch range, down from an average of 5.7 fish, Caspers said. The number of 20- to 25-inch walleyes, at 1.6, was up slightly from the average of 1.3, and the number of 25- to 30-inch walleyes was 0.4 per net, compared with an average of 0.3.
Results from the September survey showed an average of 25 young-of-the-year walleyes per net, Caspers said.
"Anything over 20 we usually consider a pretty good amount," he said. "It's not a huge year-class, but we really didn't need a big year-class now, either. We just needed a pretty good one, and that's what we got."
Perch also had a strong spring hatch, based on results from the September survey, with an average of 29.2 young-of-the-year perch per net, Caspers said; the average is 15.
"That's a pretty good amount," he said. "That's probably going to be a pretty decent year-class."
While perch numbers tend to fluctuate more than walleyes, populations of adult perch also appear to be holding steady, Caspers said. Numbers from the July survey showed an average of 11.6 perch per net, which is on par with the average of 11.5. As with walleyes, smaller perch in the 5- to 8-inch range were most abundant, with an average of 6.5 per net, up slightly from the average of 5.3, Caspers said.
Meanwhile, the survey yielded about four 8- to 10-inch perch per net, up from an average of three, and an average of one 10- to 12-inch perch per net, down from 2.4. The survey produced an average of 0.2 perch per net in the 12- to 15-inch range, down from an average of .7, Caspers said.
Perch from a record hatch in 2013 are driving the perch fishery, Caspers said. Crews in 2013 sampled 120 young-of-the-year perch per net, the highest number since the department launched the survey in 1992 and more than twice the previous record of 50.
"It seems like we get a really good big hatch like that, a spike in the perch production" every five or six years, Caspers said. "I don't know if it's coincidence or if there's something behind that.
"We're kind of in-between as far as having a lot of nice perch out there," he added. "We just have to wait for them sometimes."
White bass had a weak hatch this past spring, with 1.9 per net, down from an average of 6.1. That's not particularly concerning after a banner hatch in 2015, Caspers said. This year's adult fish survey reflected that, with an average of 19.5 white bass per net, compared with an average of 4.5. Most of the white bass were from that 2015 hatch and average 10½ to 13 inches in length.
"They'd be really low right now if it hadn't been for that 2015 hatch," he said.
Crews sampled about half a crappie per net in the fall reproduction survey, Caspers said, compared with an average of 1.6.
"We usually see a few of them," he said. "The ones that survive grow well and become nice fish."
Neither survey is particularly effective at sampling northern pike, Caspers said, but populations of North Dakota's state fish continue to do just fine in Devils Lake. The July survey yielded 3.7 pike per net, slightly more than the average of 3.1. Pike in the 21- to 28-inch range were most abundant, at 1.9, on par with the average of 2; followed by 28- to 34-inch fish at 1.6, twice the average of 0.8; and 34- to 44-inch pike at 0.2, up from an average of 0.1.
"We don't usually catch a lot of those real top end-size pike or walleyes," Caspers said. "The nets aren't geared to those. You won't be catching as many as you will with the smaller fish, even if they're as abundant."
Overall, neither survey suggests "anything to worry too much about," Caspers said.
"It would just be nice to have a few more of those keeper-size walleyes right now," he said. "But with all these young fish, they'll grow and fill in the gaps."