February 23, 2023 at 1:24 p.m.
The Lake Where You Live
Requiem for rusties?
By Ted Rulseh-
When their population exploded, they eliminated the lake's extensive cabbage weed beds and radically changed the fishery. Panfish and perch, once abundant, were decimated. Smallmouth bass gradually replaced largemouths. Walleyes' habits changed markedly.
Similar stories played out on a number of lakes. I remember back in the 1980s snorkeling on Presque Isle Lake and coming upon the skeleton of a walleye that the crayfish had picked utterly clean. Chilling is the word for that.
Now there's evidence from, of all places, the University of Illinois, that rusties in our state might be permanently on the wane. A 33-year study shows steady declines. In a couple of lakes the population has shrunk to essentially zero.
A report from the university dated February 13 observes that rusty crayfish are "one of the organisms that put invasive species on the map in the U.S. and North America ... But now we're seeing evidence in Midwestern lakes that the ecological impacts of rusty crayfish may be severe for a few decades, but may not be permanent, as we feared,"
Various factors have led to the decline in many lakes, including Birch. For one thing, almost any species that reproduces rapidly will eat itself out of house and home and come back toward a measure of equilibrium. In addition, fish soon discovered that the crayfish were good to eat and gobbled them up with gusto.
Lake associations helped keep the populations in check through trapping. Then along came a parasite that attacks the crayfishes' liver/pancreas organ with lethal effect. And a virus, also deadly. So it's no wonder the crayfish have faded.
And when the crayfish are gone or nearly so, the lakes' ecosystems start to recover. In particular, the vegetation grows back, creating habitat for snails and other water creatures, along with protective cover that helps young fish elude predators and grow to adulthood.
Things don't necessarily go back to the way they were. For example, on Birch Lake, where cabbage weed once dominated, the main aquatic plant now is coontail, somewhat less desirable and perhaps more capable of causing a nuisance if it grows excessively. Still, the perch and panfish are recovering, although slowly.
The lingering question is whether the crayfish populations will someday regenerate in lakes where they have sharply declined. The lakescapes are much less friendly to them than after they were first introduced, but there's no easy way to predict whether the population busts will be followed by booms.
The fate of rusty crayfish provides a glimmer of hope that invasive species, once established, will not necessarily remain forever. At the same time, their arrival and proliferation decades ago offers an object lesson in the devastation unwanted species can cause.
And if we need another reminder, we can look at zebra mussels, which have infested a number of lakes across northwest Wisconsin and northern Minnesota. Their impacts have been arguably just as mad as those of rusty crayfish - maybe even worse. Now is no time to get complacent about invasive species prevention as we go about enjoying our Northwoods water resources.
Ted Rulseh is a writer, author and lake advocate who lives on Birch Lake in Oneida County. His new book, "Ripple Effects," has been released by UW Press. You can learn about it by visiting my website at https://thelakeguy.net.
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