Rusty crayfish: Serious threat to waterways

It is just one more threat to our lakes, streams and rivers to worry about - rusty crayfish. The name sounds pretty nonthreatening, but these critters are a very unwelcomed nasty addition to some of our lakes, rivers, streams and ponds. 

Rusty crayfish are native to the Ohio River basin and the states of Ohio and Kentucky but, according to researchers at the Minnesota Sea Grant, these invasive crayfish are spreading quickly into Minnesota and Wisconsin waterways causing multiple ecological problems. 

We don’t exactly know all the areas where they now exist, but we do know they are in some of our premier fishing areas like Leech Lake. According to the Minnesota Sea Grant staff the first observation of rusty crayfish was in 1967 at Otter Creek in southern Minnesota. Since then, their range has expanded to approximately 50 different lakes and streams spanning 13 counties in Minnesota.

There are over 350 species of crayfish in North America and it is not always easy to identify the rusty species from some of the other crayfish that are native to our waterways. In fact, it is very difficult even when looking at side by side comparisons of rusty crayfish and native crayfish.

Research has shown that rusty crayfish displace native crayfish, reduce the amount of and kinds of aquatic plants by actually eating them, decrease the density and variety of invertebrates and can reduce some fish populations. There are no known ways to eradicate rusty crayfish once they establish themselves in a body of water. They love clean water, rocks, wood and gravel.

It is believed that rusty crayfish got established beyond the Ohio River basin by fishermen using them for bait and through pet shops where they have been sold as aquatic pets and then released into native waters. There are regulations in both states that make it illegal to introduce rusty crayfish into any waters. In Minnesota, it is illegal to sell live crayfish as bait or as aquarium pets.

The only known benefit of rusty crayfish is that they are good to eat. Commercial harvesting of them has been going on for over 40 years in Wisconsin and is now also occurring in Minnesota. 

So what does this mean to the average angler in Minnesota and Wisconsin? The rusty crayfish is larger than most native crayfish and much more aggressive, driving native crayfish out of hiding areas where they can be eaten more readily and also damaging aquatic plant life. Some research has suggested that they have hurt walleye and other fish populations, but research on other lakes offers little evidence of this. So the jury is still out on the issue.

The best advice for anglers is not to use any crayfish for bait, do not transfer any crayfish from one lake to another and be vigilant. Let’s do our part to stop them from spreading to any more bodies of water. It’s not only a good idea, it’s the law.

Ray Gildow, Staples, is the author of “Legends & Legacies, A History of the Nisswa Guides’ League” and is owner of Gildow Guide Service. More information can be found at raygildow.com.