Crayfish Catchers

Nearly 300 Minnesota lakes are home to rusty crayfish, an invasive species that can spell disaster for native aquatic plants and crayfish. These aggressive invaders quickly become the dominant crayfish in a lake, squeezing out the natives and sometimes even altering the ecosystem. Now Minnesota researchers have developed a trapping system that can reduce numbers of these destructive “rusties.”

“The main success of this project was identifying a trap type that was effective at attracting large numbers of rusty crayfish and a bait that was cost effective and easy to use,” says Brennan Pederson, field coordinator for the University of Minnesota’s Natural Resources Research Institute. The best trap turned out to be a minnow trap that’s widely available and easily modified for the purpose. 

The bait: hot dogs.

A key aim of the study was to find ways to protect vulnerable areas, including areas where wild rice grows. Wild rice, an important Native American cultural and food resource, is particularly susceptible in its spring growth period. Experiments by the 1854 Treaty Authority, an inter-tribal natural resource management organization, found that rusties tear up the roots and graze on rice shoots. The treaty authority is a partner with the NRRI on the latest “rusties and rice” project, which aims to mitigate the damage with trapping.

“Once an invasive species is established on a lake, there are very few options because whatever you do to kill that critter is going to have tons of collateral damage,” says Valerie Brady, the project manager at the NRRI. “So targeted removal tends to be one of the few things that can be done.”

The researchers tested three types of traps, baited and nonbaited, on several northeastern Minnesota lakes with wild rice or with the potential for wild rice. They found a baited wire mesh minnow trap, sold at many sporting goods stores or bait shops, worked best when modified with an enlarged entrance, trapping copious numbers of rusties and allowing for easy release of bycatch.

Brady says they want lake associations, Tribal bands, property owners, and anyone else who wants to get rid of the aquatic invaders to be able to do it themselves. “The idea was, state agencies don’t have the capacity to do this, so if people want to control rusty crayfish populations in their area, they need to do it themselves. We’re going to give them the easiest method.”

The 1854 Treaty Authority will consider using the method to protect wild rice beds, says Matt Santo, invasive species specialist for the authority.

The project was funded by the Minnesota Aquatic Invasive Species Research Center and the Minnesota Environment and Natural Resources Trust Fund.

For instructions on how to modify, prepare, and deploy rusty crayfish traps, visit the MAISRC project page at z.umn.edu/rustyremoval.