Effective rusty crayfish removals to protect wild rice

Abstract

Rusty crayfish are an aquatic invasive species that is harmful to sensitive vegetation, such as wild rice. Wild rice, which is culturally and ecologically important in Minnesota, is most vulnerable to rusty crayfish grazing during the early summer, before it reaches its emergent life stage. Currently, the best way to control rusty crayfish populations without harming other native species is to remove enough individuals through trapping. We tested different trap and bait types for removing rusty crayfish near sensitive vegetation. We also tracked rusty crayfish movement through a mark and recapture process to evaluate the feasibility of localized invasive crayfish reductions near sensitive vegetation. In 2023 and 2024, we visited 3 lakes in NE Minnesota, once in early summer and again in late summer. In the early summer, we marked and released rusty crayfish for recapture and tested different trap and bait types near sensitive vegetation. In the late summer, we continued to test different bait and trap types near sensitive vegetation while recording movement data from recaptured crayfish. Baited wire-mesh minnow traps reported an average catch rate ca. 50-fold higher than unbaited refuge shelters. Bait types performed similarly, but we suggest using hot dogs because they are effective, inexpensive, readily available, and easy to use. Rusty crayfish are capable of moving long distances in a short amount of time, with one individual traveling 438 meters overnight. Trapping close to sensitive vegetation is more protective against rusty crayfish because their ability to travel makes localized reductions difficult. We used methods any stakeholder in the state of Minnesota can use to remove rusty crayfish. Our findings serve as a guide for those looking to reduce the impact of rusty crayfish on sensitive vegetation.