The Same Lake, Two Different Smallmouth Populations Depending on the Month

A smallmouth bass population doesn't look the same in May as it does in October, even in the same lake. Biologists in Nebraska sampled one reservoir monthly from May to October in two consecutive years and found that the fish they caught skewed bigger in spring and smaller in summer and fall. That matters to managers deciding when to count fish. It might also be a useful frame for anglers thinking about which smallmouth they're likely to meet in which month.

What They Did at Lake McConaughy

The study took place at Lake McConaughy, a Nebraska irrigation reservoir built in 1941. It covers 12,140 hectares at full pool, and smallmouth bass there were first stocked in 1947 and are now self-sustaining. The authors describe it as the most heavily fished water in Nebraska, with tournament participation on the rise.

From May through October of 2024 and again in 2025, the team ran nighttime boat-mounted electrofishing at six fixed stations. They measured length and weight on every smallmouth they collected, 1,436 fish in all. Then they tracked several population measures month by month: catch per hour, how the catch split across size categories, the ratio of young fish to adults, and relative weight.

What the Numbers Showed

Monthly average catch ranged from 15 to 216 fish per hour across the two years. Catch was generally lower in spring and climbed through summer and fall. Size told the opposite story: larger fish showed up more often in spring samples, while smaller fish were more abundant in summer and fall samples.

Year to year, the lake wasn't steady either. Catch was lower overall in 2025 than 2024, and monthly catch differed between the years, particularly in July and August. The young-to-adult ratio in July swung from 0.17 in 2024 to 1.66 in 2025, a big gap for the same month.

Body condition held up. Relative weight ran between 86 and 105 across months, which the authors call "generally good body condition" for both years. It was higher in spring than in other seasons and higher in the first year than the second.

The authors also note that the Lake McConaughy patterns lined up with what's been reported for smallmouth populations elsewhere in North America. That's reassuring, but it's still one reservoir.

The Catch

This was an electrofishing study, not an angling study. The sampling was done with nighttime boat electrofishing, so these are the fish a survey crew caught, not a record of what anglers catch.

The authors also describe their results as based on a single reservoir. The authors suggest environmental factors likely explain the differences between years, noting that the reservoir's water level dropped by more than 2 meters between July 2024 and July 2025. This is one study, not a consensus finding.

What to Take Out to the Water

Everything in this section is my read, not the study's.

I've caught plenty of smallmouth in the UP, but I've never fished Lake McConaughy and I've never kept a month-by-month log of what size fish I'm catching. So I can't tell you my own trips match this pattern. What I can say is that the study gives me a reason to start paying attention. If I keep notes this year on when I catch bigger fish versus lots of small ones, I'll have something to compare against.

The practical read I'd take: if you're judging a lake's smallmouth fishery from one trip, be careful about what month it happened in. The authors conclude that sampling timing can influence the perceived population structure, so I'd be cautious about judging a lake from a single day in any one season. Whether that carries over to what ends up on your line is a question I can't answer from this paper.

Citation

Allison, Wuellner, Engel, Koupal, & Blackwell (2026). Catch me if you can: Temporal sampling changes inferences of Smallmouth Bass population structure. North American Journal of Fisheries Management. https://doi.org/10.1093/najfmt/vqag084