Life History and Distribution of the Invasive Rusty Crayfish and the Native Signal Crayfish in the John Day River, OR

Rusty crayfish (Orconectes rusticus, Girard, 1852) have been a nuisance invader throughout the eastern U.S. and southern Canada, displacing native crayfish faunas and impacting other invertebrates, macrophytes, and fish.  They were first documented west of the Rocky Mountains in the John Day River of Oregon in 2005.  To assess the spread of rusty crayfish in the basin, and to better identify the range of native signal crayfish, an extensive survey of the basin was conducted during summer 2010 and 2011 using traps, kick nets, and snorkel surveys.  In addition, one rusty crayfish-dominated site and one signal crayfish-dominated site were sampled monthly to biweekly during the spring, summer, and fall to determine population structure, estimate growth, and time reproductive events.  In the first five years since rusty crayfish were documented in the John Day, they more than doubled their range to 145 river km along the mainstem of the river.  Signal crayfish were absent from locations with rusty crayfish, consistent with the possibility that rusty crayfish are displacing natives.  Preliminary data indicate that, while rusty crayfish juveniles recruit into the population later in the year (in mid-July as opposed to spring), they grow faster and overwinter at a larger mean size, providing a potential mechanism for competitive dominance over native signal crayfish.  Our results suggest that rusty crayfish will continue to spread aggressively, and that further research and management efforts to characterize impacts and slow invasion are warranted.