Short- and long-term impacts of a major flood event on crayfish (Orconectes obscurus) in a forested stream

Due to their large, blunt bodies, crayfish are particularly vulnerable to dislodgment at high flows associated with flood events. However, little is known about their resistance/resilience to intense spates. In this study, we examined short-and long-term size-dependent recovery by a lotic crayfish (Orconectes obscurus) population following a high discharge flood event associated with Hurricane Katrina (2005). Short-term population recovery was assessed using mark-recapture sampling in a riffle-shallow pool-riffle sequence. Crayfish were marked with Visible Implant Elastomer tags the morning of the rainstorm and recapture attempts occurred 2, 8, 10, and 16 days post-flood. The crayfish population in riffles returned to pre-flood densities within 10-16 days, however, the shallow pool population did not. Recovery was size-dependent with small crayfish returning to pre-flood densities within 16 days, while large crayfish did not recover during this time interval. Although crayfish showed short-term effects, this flood event had limited impact on crayfish densities on a longer time scale (assessed using seasonal density estimates collected on a reach scale). For example, summer 2005 (similar to 2 months pre-flood) and summer 2006 (9 months post-flood) densities were not statistically different from each other for either small or large crayfish. Small crayfish resilience/resistance may result from movement into areas of lower hydraulic stress to avoid high current velocities, whereas large crayfish may require a complete growing season for recovery. Resistance to flooding by small crayfish may be the key component to long-term population persistence of crayfish populations in flood-prone streams.