Minnesota + Wisconsin Perch Problem, Shrinking In Size + Population

Minnesota and Wisconsin has a perch problem.  And it's probably not what you think - especially if you're a regular angler.

Ecologically speaking, perch exist near the bottom end of the food chain for lakes and rivers.  Small in size, they make perfect feeding for other species of fish that inhabit the same waterways.  That small size has also made them less-desirable to many anglers who are looking for a catch that's big enough to make a meal out of the days take; usually the bigger ones end up coming home to the frying pan.

But something is wrong and it's causing this species of fish that's always been small in size to shrink even further.  Additionally, the population of the fish is decreasing as well.  The combined problems have local Department of Natural Resource officials scratching their heads and inventing new ways of sampling the fish.

The reduction in length of the fish is measurable.  An article in the Superior Telegram - which outlines the problem from the vantage point of the Minnesota Department of Natural Resources - explains the situation:

"Big perch, those over 5 inches, have been declining dramatically over the past 50 years. 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 1970's 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".

The assessment from the Minnesota Department of Natural Resources also elaborates on the shrinking size of the perch they do find in sampling:

"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."

Something is wrong and DNR officials want to know why.  Bethany Bethke, a Fisheries Biologist for the Minnesota Department of Natural Resources sums up the situation:  "[s]uddenly this litt;e fish that everyone took for granted is undergoing some big changes".  And,  the DNR wants to know why.

One of the issues combating the research involved changing the way the DNR obtains samples.  In-the-field researchers realized that the mesh on the nets they were using was too big to catch larger size samples of perch.  That void leaves fluctuation to sampling wide open.

To change that and to work towards getting a bigger and more representative sample, the DNR has started instituting electro-shocking and dip-netting to its standard procedure. For the time being, it looks like it's working - but it's still too soon to be sure.  "...[I]t will take many more years of data to see if small perch are declining as fast as big ones".

The changes to the sampling have led to a discovery:

"What researchers have....found out....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."

One other discovery and item at play in the problem:  female perch tend to be bigger in size.  It's usually the larger perch that anglers keep.  Current fishing regulations in Minnesota allow a fisherman to 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.  ....[T][hat means they're keeping females." Fishing female perch out of the lake might lead to the decrease in population sizes.

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For now, the spotlight is on the decline of perch in Minnesota.  But like anyone who lives on the border knows, nature doesn't recognize borders.  Minnesota DNR official Beth Holbrook concedes "Wisconsin is looking at a decline in perch, too, and some other states, so it's not just a Minnesota issue."