Minnesota has a problem with perch, its 'keystone species,' and causes may vary
Department of Natural Resources biologists are studying why perch are shrinking in size and number.
DULUTH -- Pity the poor perch. As just about every other fish in Minnesota lakes is trying to eat them, most never have a chance to grow up.
And then when some of them actually do get big, we people like to catch, cook and eat them.
Across Minnesota, from the prairie to the Boundary Waters, yellow perch “may be the most important link between lake productivity and the well-being of predatory fish species’’ such as walleye, pike and bass, the DNR’s lake management guide notes. Perch are also the fish that kids may catch most off docks. And they fill up buckets for hungry ice anglers all winter.
“It’s really a keystone species in this state, both in terms of forage for our popular game species, but also, in some areas, perch are a big deal for people to keep and eat,’’ said Bethany Bethke, a fisheries biologist for the Minnesota Department of Natural Resources.
But Minnesota is having a big perch problem. Big perch, those over 5 inches, have been declining dramatically over the past 50 years across the state. No one is sure yet why, or what impact the decline is having on the fish that eat perch. But DNR assessment netting since the 1970s has shown a 30% decline in perch nearly statewide, and some lakes that had perch 50 years ago are now seeing none showing up in DNR nets.
And the big perch aren’t just declining in number, they’re also declining in size. New data collected from over 1,000 Minnesota lakes found that perch shrunk by a half-inch statewide over the past 25 years. In a quarter of the lakes, the decline was three-quarters of an inch.
“Suddenly, this little fish that everyone took for granted is undergoing some big changes,’’ Bethke said.
Developing new methods
Researchers realized that they weren't getting little perch to study because the mesh in the usual DNR survey nets was too big to catch them. So Bethke and other scientists, including the DNR’s Beth Holbrook, are developing the best ways to survey perch under 5 inches. They are testing both electro-shocking and then dip-netting the stunned little fish in shallow waters, as well as using traditional seines with a smaller mesh size in deeper lakes.
Both methods are working, depending on the lake, and the DNR is now getting data on perch as small as 1.5 inches long. But it will take many more years of data to see if small perch are declining as fast as big ones.
What researchers already have found out, however, is that there are entire populations, sometimes all the perch in any given lake, that never get as big as 5 inches. In some lakes, female perch are maturing at 3 inches, whereas in some lakes, they don’t start reproducing until they hit 7 inches. Those 3-inch reproducing females almost never get very big.
“In some lakes we've looked at (using the new survey methods), it turned out that, yes, there really were no perch,’’ Bethke noted. “But we’ve also found a lot of little perch in lakes where the big ones have declined or are absent. ... There are perch populations we just didn't know about before because they don't get very big.”
The latest perch project so far has looked at perch from 30 lakes across the state, from Windom to Finland, with fisheries staff from 20 local DNR fisheries offices doing the field work.
The study has found that in lakes where perch grow faster they tend to die young, living short lives. But in clear, colder, less fertile, slow-growing northern lakes, researchers found perch up to 17 years old, a jaw-dropping age for any fish species that’s eaten by so many other fish.
“Everything likes to eat perch,’’ Holbrook noted.
The size of the lake, water clarity and how far north or south the lake is located in the state also seem to be factors in the perch decline.
Big perch are female
Another early finding is that nearly all of the big perch being netted by the DNR are female, up to 100% of them in some lakes. Researchers don’t know yet what that means for the long-term viability of the perch population, or if that's a new phenomenon. But it clearly means that anglers who are harvesting jumbo perch are taking out breeding stock. And if the data holds true, that may mean calls for reduced bag limits on big perch, much as anglers have seen with bluegills, crappies and game fish like walleye.
Currently, anglers across Minnesota can keep a bucket full of 20 perch of any size, although most anglers won’t keep them until they get to be about 8 inches or so. And that means they are keeping females.
“That’s a really interesting point … But we still need more data before we can make any conclusions on harvest levels and bag limits, that sort of thing,’’ Holbrook said. “That may be something that comes up in the future.”
While researchers have developed better ways to survey the perch decline, finding out what’s causing it is the big question most anglers want answered, Bethke and Holbrook agreed. Their first guess is increased predation by big fish. The bigger species, like bass, walleye and pike, have had mostly stable populations across the state in recent decades and may be eating more perch. Big perch also eat a lot of little perch.
But the problem also may be climatic or environmental, some major change or changes happening across an entire region, such as warming water temperatures or invasive species.
“Wisconsin is looking at a decline in perch, too, and some other states, so it’s not just a Minnesota issue,’’ Holbrook noted.
Another factor may be habitat. Studies have found a major decline in coarse, woody material along the shoreline of lakes where perch like to spawn. That woody structure has often been removed as new homes and cabins are built on shore.
The researchers note that some lakes might be seeing a decrease in big perch, which might be bad for anglers who want to eat perch, but an increase in little perch, which might be good for walleyes and pike.
“Maybe having a lot of little perch is better to support the predator fish,’’ Holbrook noted. “That's’ an entirely different management objective than a lake where anglers want to keep big perch to eat.”
About Minnesota perch
Yellow perch are found in lakes, rivers and streams across Minnesota but are most abundant in lakes and backwaters of large rivers.
The largest perch recorded in Minnesota was caught in Lake Plantagenet in Hubbard County and weighed 3 pounds, 4 ounces.
While not typically targeted by sport fish anglers in the summer, perch are highly sought after by ice anglers. They have firm, very good tasting flesh that rivals that of their larger cousin, the walleye. Some people say it tastes better than walleye.
Perch have a stocky, torpedo-shaped body. They are pale yellow to bright orange with six or seven dark, vertical bars on their side. Their mouth is small and points forward.
Perch swallow their food whole because their esophagus, the tube between the mouth and stomach, is flexible. A fish esophagus usually can handle anything that fits into the fish’s mouth. It can even adjust mid-swallow in case the fish eats something that happens to be too big to fit.
Female yellow perch mature between 2 and 4 years old, males usually mature one year earlier. Spawning takes place in April and May when water temperature reaches 45-52 degrees. Their method of spawning is unique in that female perch lay their eggs in long gelatinous strands, usually floating or hanging from vegetation or some other structure. The average female will lay approximately 23,000 eggs. Eggs hatch in eight to 10 days.
Perch are relatively short-lived fish. Few over 7 years old are ever caught, although one in Minnesota reached age 17.
Perch are food for largemouth and smallmouth bass, northern pike, musky, walleye, bowfins, burbot, lake trout and other fish as well as gulls, mergansers, loons, kingfishers, eagles and herons and otters.
John Myers reports on the outdoors, environment and natural resources for the Duluth News Tribune. He can be reached at firstname.lastname@example.org .