Chicago Sun-Times - - OUTDOORS - More on Keller Lab is at keller­­lab. ✶ dbow­man@sun­ @Bow­manout­side DALE BOW­MAN

Af­ter Rachel Egly and Thomas Knapp tied up the Tracker Top­per 12W, they set three plas­tic tubs of in­va­sive cray­fish on the dock at River Park. male red swamp cray­fish vig­or­ously waved its long claws from in­side its tub. They also brought back a fe­male red swamp, with smaller claws, and a rusty cray­fish.

Egly and Knapp were mid­way through check­ing traps last week as part of an on­go­ing study of in­va­sive cray­fish.

Nor­mally they see “a whole lot of in­va­sive red swamp cray­fish and rusty cray­fish,” Egly said. “Oc­ca­sion­ally, we see a few na­tive white river and cal­ico cray­fish.”

At a con­fer­ence last year, I sat next to Reuben Keller, an as­so­ciate pro­fes­sor at Loy­ola Univer­sity. He men­tioned trap­ping in­va­sive cray­fish on the Chicago River. Keller founded the Keller Lab, an aquatic in­va­sive ecol­ogy re­search lab at Loy­ola. Egly is the lab man­ager.

The pan­demic side­lined plans for me to ride along while they checked traps. Even do­ing the sur­vey for a third year was in ques­tion. But, they were cleared to start in July. Nor­mally, they check traps twice a week from June through early Oc­to­ber.

In 2018 and 2019 they did a 100-me­ter stretch of traps just up­stream of the launch at River Park and a 100-me­ter stretch just down­stream. The con­trol sec­tion was far­ther up­stream.

Their trap­ping dropped the pop­u­la­tions to one third com­pared to the con­trol sec­tions, from 1.2 per trap in the con­trol to 0.4 in the trap­ping area. By 2019, it was more strik­ing: 1.5 vs. 0.3 or 0.4.

Ex­per­i­men­ta­tion found cheap hot dogs made the most ef­fec­tive bait. They also learned to set the traps closer to­gether. In a study, Egly used nail pol­ish to mark and num­ber cray­fish re­leased and re­cap­tured.

“Rarely were they more than 10 me­ters away, some­times they were even [re­caught] in the same trap,” Keller said.

So Egly set traps five me­ters apart. Red swamp cray­fish are cen­tered on the North Shore Chan­nel and the North Branch near River Park. Den­sity lessens closer to the Wil­mette con­nec­tion to Lake Michi­gan.

They have trapped very few far­ther down­stream on the North Branch. Keller spec­u­lated that it is ei­ther dif­fi­culty trap­ping there or the deep sharp walls are not fa­vor­able.

As invasives, red swamp cray­fish sup­plant or push out na­tives. As a bur­row­ing cray­fish, they in­crease tur­bid­ity and un­der­mine levies.

“They’re vo­ra­cious om­ni­vores, they’ll eat about any­thing,” Keller said.

They eat aquatic veg­e­ta­tion, lead­ing to de­struc­tion of im­por­tant nurs­ery habi­tat for young fish.

But red swamp cray­fish have a weak­ness born of strength.

“Red swamp cray­fish are al­ways want­ing to fight and they are much more ag­gres­sive,” Keller said.

But a fight with a fish is not fair. For cray­fish.

Trap­ping ef­fec­tively re­duces red swamp cray­fish. Egly emailed that in 2019 they re­moved “97 pounds of in­va­sive red swamp cray­fish from the North Branch and North Shore Chan­nel in just four months of sam­pling.” In 2019, they caught 3,400 red swamp cray­fish. On an av­er­age sam­pling day, they catch about 275 cray­fish.

Keller and his team plan to study what fish in the area are ef­fec­tively eating cray­fish. They plan to pig­gy­back with the Illi­nois Depart­ment of Nat­u­ral Re­sources and U.S. Fish and Wildlife Ser­vice in reg­u­lar Asian carp sur­veys to col­lect some fish. If cer­tain species are more adept at prey­ing on red swamp cray­fish, it might make sense to stock them for con­trol.

Since re­moval of the dam on the North Branch at the con­flu­ence with the North Shore Chan­nel, finds of na­tives in­creased. In 2018, they found no na­tive cray­fish. Now they are find­ing three or four na­tives a day. “That is re­ally cool,” Egly said. Be­fore the cray­fish in the non-con­trol sec­tions are frozen (eu­th­a­nized) at the lab, data is taken on sex (males are di­vided into Form 1, sex­u­ally ac­tive, and Form 2), size and weight. Red swamp cray­fish most likely ar­rived as re­leased class­room pets. Other pos­si­bil­i­ties are as dis­carded fish­ing bait or left­overs/es­capees from cray­fish boils.

As Egly and Knapp prepped to fin­ish check­ing traps, four women pad­dlers spot­ted the cray­fish, then asked ques­tions. A bright red hand-sized cray­fish look­ing ready to break into Zoid­berg’s voice and wav­ing out­sized claws will draw ques­tions.

Egly pow­ered the 5hp Mer­cury on the Tracker from the dock and headed up­stream on the North Shore Chan­nel.

It was a time.

As Keller, his daugh­ter Su­san­nah and I walked off, a fa­ther and son, who had waited pa­tiently, came out to shoot a dance video. TikTok on the Dock.


View from the south­east of the re­worked area at the con­flu­ence of the North Branch of the Chicago River and the North Shore Chan­nel at River Park, where Loy­ola Univer­sity stu­dents trap and study in­va­sive and na­tive cray­fish.


An in­va­sive male red swamp cray­fish, trapped from the North Shore Chan­nel, reaches from a plas­tic tub.


The red swamp cray­fish is de­scribed as a “vo­ra­cious om­ni­vore” that isn’t picky about what it eats.

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