The findings, part of an ongoing study at the University of Wisconsin-Madison, suggest that the type of interaction among rusty crayfish, fish and aquatic plants may tip the scale, favoring either the invader or native species. This knowledge, the researchers note, may lead to new strategies for removing these trespassers.

Details of the research will be presented Wednesday, Aug. 4, at the annual meeting of the Ecological Society of America in Portland, Ore.

Native to the streams of Ohio, Kentucky and Tennessee, rusty crayfish - measuring up to five inches long - have slowly infiltrated lakes far and wide, including those in New Mexico and Ontario.

Once used for bait, rusty crayfish now are partly responsible for anglers' declining number of fish catches because they alter fish habitat, ultimately altering fish populations.

For example, these intruders eat fish eggs, displace animals native to the waters and "mow down" aquatic plants - a source of food and shelter for fish, says Brian Roth, a graduate student at UW-Madison's Center for Limnology and a presenter at the meeting. "They have really dramatic and traumatic effects on the ecosystem."

To date, the promise of successfully removing rusty crayfish and restoring the habitat has been bleak. For example, bait traps tend to catch only the largest rusty crayfish, and biocides, chemicals proven to wipe them out, obliterate everything else in the lake.

But one strategy for managing these invaders once they enter a lake might come from Roth's preliminary data showing that lakes - even ones similar in water chemistry and the amount of rocky substrate crayfish call home - can have either a low or high abundance of these invaders.

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Contact: Brian Roth
bmroth@wisc.edu
608-262-3087
University of Wisconsin-Madison
1-Aug-2004