( d the fish populations are returning to...)Study shows hope for ridding lakes of clawed invader

The two-pronged approach to ridding Sparkling Lake of its rusty crayfish is the key, notes Jake Vander Zanden, a UW-Madison professor of limnology who is helping oversee the experiment. "One important message is that trapping alone will not do it. There's a synergistic effect with the fish playing an important role."

Smallmouth bass and rock bass, says Vander Zanden, are the primary predators of juvenile crayfish, and to some degree sunfish - bluegills and pumpkinseeds - pitch in by eating the smallest crayfish. The Wisconsin DNR, by manipulating the bag and size limits for anglers fishing Sparkling Lake, has helped establish an optimal population of the fish that routinely dine on the crayfish.

The trapping on Sparkling Lake, however, has been intensive during six years with 280 traps seeded around the lake. Baited with beef liver, the traps snare both native and rusty crayfish, but the natives, Carpenter explains, are returned to the lake. The trapping targets the largest crayfish, those that may be too big for the lake's predators.

The big hope, says Carpenter, is that the experiment will expose a "tipping point," where the combination of trapping and pressure from predator fish pushes the rusty crayfish population to crash, with the lake ecosystem returning to its pre-rusty crayfish state.

"What we are wondering is whether we will reach a tipping point where the fish alone can keep up the pressure," says Carpenter, an authority on such ecological change. "We haven't seen it yet, but we're not prepared to admit there isn't a tipping point."

Vander Zanden says the rusty crayfish infestation in Sparkling Lake, like most lakes where it is found, was probably sparked by a small pioneer group that somehow got into the lake. At one time, rusty crayfish were used as bait. Misguided attempt
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Source:University of Wisconsin-Madison