The Rusty Crayfish

[Mike Clifford]

Ran across an interesting article while looking for something completely unrelated (isn't that how it works on the internet?):

 

"Crayfish are omnivores," Kratz said, and one of their favorite foods is "the slimy scum" that coats the leaves of aquatic plants.

 

But while a native crayfish will gently climb a plant's stalk to scrape away at a leaf, a rusty will knock the whole plant over by snipping it at its base, leaving swaths of denuded terrain on the bottom of several northern lakes.

 

That's a bad-azz species there, huh?

 

The point of my post is actually to ask a question in the hopes somebody might have some sort of answer.

Here is another quote from the article (the full text can be viewed HERE:

The battle against invasive aquatic species has largely been a losing one, with the few victories coming at a sizable cost to native species, water quality and budgets.

 

As most anglers know, it is illegal to possess live rusty crayfish in Illinois.

So what is the best way to eradicate this species, and in doing so- what effect does it have on the native fish populations?

They eat these crayfish as well, right?

[Steve S.]

I would imagine they eat them. Do they grow larger or are they more aggressive than native craws? Larger claws? Maybe they reach an undesirable size for all but the orniest bass (is that a word?).

 

Another Tim subject?

[Tim Smith]

I would imagine they eat them. Do they grow larger or are they more aggressive than native craws? Larger claws? Maybe they reach an undesirable size for all but the orniest bass (is that a word?).

 

Another Tim subject?

 

Rusties were responsible for drastically reducing the amount of aquatic vegetation in numerous lakes in the upper midwest. Ironically, they came from a bait bucket introduction in Wisconsin and northern Illinois, but they are native to Indiana and Kentucky. In Wisconsin, rusties attain large sizes very quickly and also have larger claws than the native crayfish in the area. Rapid early growth gets them out of their vulnerable early stages and increases their survival and their densities. Large body size and large claws also helps them fight with other crayfish more successfully to compete for refuge. Crayfish that can't find good refuge are exposed to fish predators and have much lower survival rates. Rusties also hybridize with the clear-water crayfish and will gradually eliminate them from habitat by forcing the females of other species to produce infertile hybrids.

 

Rusties affect not only plants and other crayfish, but also other invertebrate species. Streams and rivers and especially lakes change dramatically when rusties enter an area. Studies at Michigan State also indicate rusties may be successful predators on fish eggs.

 

I was involved with a study on Jackson and Prairie Creeks at the old Joliet Arsenal in which we trapped crayfish and recorded their behaviors and responses to bird predators. At the time, Praire Creek had no rusties and we trapped about just a few crayfish per night in each trap. That's typical for a nightly set in a stream. In Jackson Creek, we trapped up to 100 rusty crayfish per night. Their densities were just staggering. While that seems like a robust forage base for smallmouth and other species (and we did collect some big smallies there) it is important to remember that the rusties got that dense because for the most part, they were difficult to catch. Combine that with their effects on fish eggs, the loss of alternative forage types, the loss of plant cover and rusties are bad news for a fishery.

 

Presently, the range of rusty crayfish is still expanding in Illinois. They are present in Dawson Lake near Bloomington, which means they will probably eventually enter the Sangamon basin rivers. They are common in the Rock (and must also be in the Kankakee). I'm pretty sure they're common in the Chicago area as well (although I don't have a specific memory of where and I don't have a map or journal here to find out). Basically...they're coming soon to a stream near you...and..

 

...unfortunately, rusties are probably here to stay. There are programs underway to study rusty crayfish eradication through means such as bottom trawling, but the prognosis for that method seems bleak. We're going to have to learn to live with them and just do our best to slow their advance as much as we can. It is also unfortunate that we anglers have been blamed for the spread of rusties. This is a good case study for why it is a bad idea to carry bait from one system to another, even if the other system is just a short distance away.

 

Rusties can be identified a rust colored spot that occurs on the sides of their abdomens (the cephalothorax) just ahead of the tail. They should also have black rings near the tips of the claws with a paler orange area at the extreme tip. No other crayfish in Illinois will have those things together.

[Steve S.]

Tim

 

Impressive details and a quick response.

 

Is Prairie Creek the one that flows through Midewin? If so, I waded there with my daughter, mostly exploring and photographing. Found a beautiful Map Turtle. Also saw hordes of crayfish and some respectable bass (I believe it is a no fishing zone). Netted an interesting darter, but did not photo or get an ID.

 

Have the rusties spread by other means?

 

If they are native to IN, then wouldn't they naturally be in the Kankankee and connecting tribs?

[Tim Smith]

Tim

 

Impressive details and a quick response.

 

Is Prairie Creek the one that flows through Midewin? If so, I waded there with my daughter, mostly exploring and photographing. Found a beautiful Map Turtle. Also saw hordes of crayfish and some respectable bass (I believe it is a no fishing zone). Netted an interesting darter, but did not photo or get an ID.

 

Have the rusties spread by other means?

 

If they are native to IN, then wouldn't they naturally be in the Kankankee and connecting tribs?

 

That's the stream, Steve. The rusties were in Jackson, back in '99 but are now moving into Praire. There is a study underway right now by Chris Taylor to look at their specific effects on the food web as they enter that stream. That will be a first for Illinois.

 

I think the invasion into Prairie Creek was a simple migration upstream.

 

...and I think it's southern Indiana and Kentucky where they are native, not northern Indiana.

[Guest rich mc]

while doing theclean up on the east branch of the dupage this spring, most crayfish picked up withthe trash were rusties. this was per don labrose the biologist .

[Tim Smith]

Put those brown bass into the lakes.

 

The ones in the rusty-infested fisheries up in WI are doing a decent job of eradicating the craws... Though not the best of job, but do-able.

 

Smallies are common in the areas where rusties have invaded. They (and the other larger predator fish that are there) can make a difference in rustie numbers, but the strongest determinant of crayfish numbers is the available cover. Bass can't catch crayfish out of rock refuges until they come out into the open. They also have a hard time finding them in dense stands of rooted vegetation. If you fill up a lake with rock, you are filling it up with crayfish. Vegetation will hold them as well (until they graze it down).

 

What you'll see in lakes with predators and crayfish are "grazing halos". The crayfish live in cover and come out at night to graze. They can travel a certain distance from cover before they have to retreat at the end of the night. The vegetation inside the "halo" where the crayfish can forage gets hammered pretty hard.

 

Crayfish that get caught out of cover in day light areas get eaten (unless they are too large...10% of bass body length excluding the tail unless they are molting).

 

Remember too that rusties have a nasty pinch compared to most crayfish. They do a better job of fighting off bass than most other crayfish species.