Apparent decline in Minnesota's perch has officials concerned

An apparent long-term decline in Minnesota's yellow perch populations has Department of Natural Resources fisheries officials perplexed and seeking answers.

A recently published study showed a significant decline since 1970 of yellow perch caught in DNR nets. Perch are a primary food for walleyes, northerns and largemouth bass, so a drop in perch numbers could spell wider troubles.

The study said the trend is important "because the decline of this species may negatively impact angling opportunities and food webs across the state.''

And larger perch themselves are targeted by many anglers, especially in winter.

"It's definitely a statewide concern,'' said Brad Parsons, DNR central region fisheries manager. "Perch are a vital component of our fish communities.''

There are several hypotheses, and a prime one is an increase in predator fish, including walleyes, northerns and bass, that feed on perch, said Bethany Bethke, a DNR researcher and co-author of the study.

"We have had an increase in predators,'' Bethke said, which includes "hammer-handle'' northerns in many lakes — a separate issue the DNR also is trying to resolve.

But the study shows the perch decline hasn't just occurred on lakes with high northern populations; it's more widespread.

"We think it's a combination of things,'' she said. "We've also had habitat loss — vegetation and woody debris — that makes it harder for perch to reproduce.''

Another possibility is that perch haven't declined, but their size has shifted and they aren't showing up in DNR nets, which don't capture perch smaller than 4 inches.

"Maybe there's still enough [small perch] out there for predators to eat,'' Bethke said. "All we know is there's been a general decline in the catch of perch [in DNR nets]. Whether it's all perch or just larger perch, we don't know.''

Other habitat changes, including increasing water clarity and more vegetation, also could be affecting the DNR surveys.

"It also could be a signal of lakes changing over time, whether because of climate change, or development or our own management activities,'' Bethke said.

Melissa Treml, DNR fisheries research manager, said the perch trend is concerning.

"We have formed a group to look into it so we can try to identify a cause,'' she said.

Doug Smith • dsmith@startribune.com

Twitter: @dougsmithstrib