This project's goal was to determine which trapping methods are most effective for protecting sensitive vegetation like wild rice from rusty crayfish grazing and evaluate effectiveness of localized removals through recapture of marked crayfish.
Background:
Rusty crayfish (Faxonius rusticus) are native to the 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 take after their name and can be easily identified by a prominent rusty-red spot on either side of their carapace. This rusty spot can vary in size and color, but it is the most obvious identifier for rusty crayfish.
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Wild rice is an important resource that provides critical habitat to aquatic invertebrates and young fish while also stabilizing wetland soils with their roots. It is culturally important for tribal nations in the upper Midwest. Rusty crayfish are omnivores that eat and uproot aquatic vegetation. Wild rice is vulnerable to rusty crayfish grazing and is particularly sensitive to disturbances in its growth during spring (May- June) when young, tender shoots are rising from lake bottom to the water’s surface.
Activities:
MAISRC researchers evaluated three different types of traps and baits for trapping rusty crayfish. Researchers visited three lakes in 2023 and 2024 in two different seasons (spring and summer), spending three consecutive nights trapping rusty crayfish at each lake each season. Two trap types were baited, and one trap type was non-baited. During the spring sampling session, researchers marked and released some rusty crayfish with the hope of recapturing them during the summer sampling session. Recaptured rusty crayfish helped the researchers learn how far rusty crayfish moved between seasons to determine if crayfish removals near wild rice were sustainable. The goal is that these findings will provide those interested in controlling rusty crayfish with guidance on how to effectively control them using trap and bait choices legal in Minnesota.
Research findings:
Rusty crayfish trapping in Minnesota lakes is showing promise but requires significant effort to be effective. These invasive crayfish can be caught in large numbers using standard minnow traps baited with inexpensive options like hot dogs, but population control requires intensive trapping efforts.
While refuge traps (traps offering spaces to hide) offer a non-baited alternative trap style, the low capture rate for crayfish raises questions about their viability as a control method. Refuge traps did capture a higher proportion of female crayfish compared to the baited traps, but the low capture rate meant that the baited traps captured more female rusty crayfish overall. Female rusty crayfish carry eggs and can start an entirely new population individually, so they are the most important crayfish to remove when engaging in population control. The extremely low catch rate of refuge shelters compared to baited traps does not make refuge traps a good choice for population control. Baited wire-mesh minnow traps were the most effective trap tested. A concern before testing traps was that the standard baited trap would become full and allow crayfish to escape. This concern proved unfounded because, by MN law, traps must be checked daily. The XL baited trap had a similar catch rate per a 24-hour period, so it is unlikely crayfish were escaping the standard baited trap. Hot dogs proved to be an effective bait that is inexpensive, readily available, and easy to use.
Rusty crayfish are highly mobile, traveling distances of up to 630 meters overnight, making re-colonization likely even after an area is trapped thoroughly. MAISRC researchers did not observe a decrease in catch rates between spring and summer trips while trapping for 3 nights consecutively each trip. Further research is needed to determine if a more intensive trapping routine can suppress rusty crayfish populations near sensitive vegetation. Because rusty crayfish demonstrated impressive mobility, researchers recommend trapping immediately adjacent to sensitive vegetation in need of protection. Licensed anglers need an infested waters permit to trap rusty crayfish and traps must be tagged by MN DNR Fisheries staff (this follows MN minnow trapping regulations; the same permit is used). While there is no daily harvest limit on crayfish, but there is a possession limit of 25 pounds of whole crayfish at any given time. A person wishing to take or possess more than 25 pounds of whole, freshwater crayfish must first obtain a commercial permit. Learn more from the MN DNR here.
Interested in trapping rusty crayfish?
Download a free guide to trapping rusty crayfish in Minnesota, written by Valerie Brady and Brennan Pederson of MAISRC. EDDMapS is an online interactive map that shows reports of rusty crayfish infestations in different waters across the midwest. Look here to find where rusty crayfish have been identified.
Rusty crayfish can be found across 35 counties in Northern, Central, and Southern Minnesota. If you want to help protect sensitive vegetation from rusty crayfish in your favorite lake, you can! The methods used to trap crayfish were intentionally developed so any interested resident in the state of Minnesota can follow the process as long as they possess a valid MN fishing license and obtain an infested waters minnow trapping permit (free).
Media:
- Hot dogs and minnow traps: an effective approach to controlling invasive rusty crayfish, WTIP
- 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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