The Lake Where You Live

None of us want invasive species in our lakes. But what happens when a non-native species that invaded becomes an integral part of the ecosystem?

I refer specifically to rusty crayfish, and I can make a case that this species, though obnoxious when it first appears, can become beneficial and have negative effects when it disappears.

When rusty crayfish infest a lake, property owners’ first response is: Let’s get rid of them. That’s fully understandable, as I can attest from my experience on Birch Lake. Their population here exploded some three decades ago. Shine a flashlight down from the pier at night and the shallows would be crawling with rusties, enough to give someone the creeps.

The crayfish wiped out the lake’s extensive cabbage weed beds and upended the fishery. Perch and panfish, once abundant, became scarce. Walleyes were hard to find. The Friends of Birch Lake began trapping and removing the crayfish, with some effect.

Then something interesting happened. Smallmouth bass, previously rare or non-existent in the lake, took hold and thrived in the largely weedless, rocky environment. In what I learned is the typical pattern with rusties, fish figure out how to eat them. Perch and bluegills gobble up the little ones. Smallmouths feast on the larger ones.

Meanwhile, through overpopulation, the crayfish essentially eat themselves out of house and home. That, along with fish predation (and an assist from trapping) brings the population into a sort of equilibrium.

When that happened here on Birch Lake, we had good walleye fishing, and a trophy smallmouth population — catching fish upwards of 20 inches and pushing five pounds became routine.

Then the crayfish population crashed. A few summers ago, as I snorkeled along a shoreline, I saw one or two crayfish dart away with every kick of a flipper. A year later on a similar mission I saw far fewer. Then last year, snorkeling for nearly half a mile out and back, I saw none — no crawdad, craw-mom or craw-child. 

The likely reason? DNR researchers have found that the rusties are vulnerable to a virus, and to a parasite that attacks their equivalent of a liver/pancreas. Those two afflictions have wiped out rusty populations in a number of northern lakes.

And what is the consequence here on Birch Lake? Our smallmouth bass population has plummeted. The rusties’ disappearance eliminated what had been a major and possibly the primary item on the smallmouths’ menu. The big, muscular bass that used to prowl the rock bars are now very hard to find.

One could argue that although the crayfish at first were an unwelcome rapacious invader, they eventually became a part of the food web; there was no reason to hate them just because they came from somewhere else, were not native to Wisconsin.

Would I wish rusty crayfish on any other lake? Definitely not. Would I want them back in Birch Lake? That answer isn’t as easy. They did considerable damage, some of which persists: the cabbage weed they decimated is now being replaced by less desirable coontail, growing in some areas toward nuisance proportions.

So I guess my answer is that I would prefer the crayfish never came to Birch Lake. But I also mourn the big hole their departure has left in the lake’s food supply, and as a consequence in its fishery.

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 his website at https://thelakeguy.net.