This project's goal was to determine which trapping methods are most effective for protecting wild rice from rusty crayfish grazing and to evaluate long-term sustainability of localized removals through recapture of marked crayfish.
Background:
Rusty crayfish are native to the United States’ Ohio River Basin. They were likely introduced and spread through the improper use and disposal of live bait. The species is also commonly imported and sold by the aquarium trade, and to schools by biological supply houses, leading to the potential for illegal release into the wild. The first established population in Minnesota was in Lake Superior in the late 1990s. Rusty crayfish is a regulated invasive species in Minnesota, which means it is legal to possess, sell, buy, and transport, but it may not be introduced into a free-living state, such as being released or planted in public waters.
Rusty crayfish eat and uproot aquatic vegetation. Wild rice is an important cultural resource vulnerable to rusty crayfish grazing, and is particularly sensitive to disturbances in its growth during spring (May- June) when young and tender shoots are rising from lake bottom to the water’s surface.
Activities:
MAISRC researchers evaluated trapping methods of rusty crayfish among three different types of traps and baits, and in two seasons (spring and summer). During the spring sampling, researchers marked and released some rusty crayfish which were recaptured during the summer sampling. Recaptured rusty crayfish helped the researchers learn how far rusty crayfish moved between seasons to determine if localized reductions near wild rice were sustainable.
The findings will provide stakeholders (lake associations, community groups, soil and water conservation districts, and Native American bands) with guidance on effective rusty crayfish control using trap and bait choices legal in Minnesota. The findings on rusty crayfish movement rates will inform stakeholders how long trapping efforts near sensitive vegetation may be protective.
Research findings:
Rusty crayfish trapping in Minnesota lakes is showing promise but requires significant effort to be effective. These invasive crayfish can be caught using standard minnow traps baited with inexpensive options like hot dogs, but population control demands intensive trapping efforts.
While refuge traps (traps offering spaces to burrow and hide) have been tested, the low capture rate for female crayfish raises questions about their viability as a control method. Rusty crayfish are highly mobile, traveling distances of up to 630 meters overnight, making re-colonization likely even after an area is trapped out. Professional trappers are often needed to manage populations effectively due to the extensive work involved. However, licensed anglers can harvest up to 25 pounds of any crayfish for personal consumption. A person wishing to take or possess more than 25 pounds of live, whole, freshwater crayfish must first obtain a permit. Learn more here.
Media:
NRRI research confronts rusty crayfish challenge, NRRI
UMD researchers tackle how to remove invasive species inside boats, Duluth News Tribune
On the water front: invasive lake species, UMN News
Collaborating partners:
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