POPULATION RESPONSE OF THE INVASIVE CRAYFISH ORCONECTES VIRILIS (HAGEN, 1870) (DECAPODA: ASTACOIDEA: CAMBARIDAE) TO RESTORATION: WHAT ARE THE CONSEQUENCES OF CHANGES IN PREDATORY REGULATION AND PHYSICAL HABITAT IN FOSSIL CREEK, ARIZONA, USA?

We examined the response of a population of an invading non-indigenous crayfish, Orconectes virilis (Hagen, 1870), to a stream restoration project in travertine-forming Fossil Creek, Arizona, USA. Restoration included the re-establishment of the natural flow regime after the decommissioning of a dam and removal of non-native predatory fishes. The goal was to determine if changes in the dominant predatory fishes or changes in physical habitat variables, including substrate modification and base flow influence changes in crayfish abundance. We predicted that increased and unregulated flows and velocities would not generally decrease crayfish abundance, and that the removal of non-native fishes would increase the number of crayfish while local substrate modification by travertine deposition, a form of limestone which fills in interstitial spaces, would decrease the number of crayfish. Consistent with our predictions, there were not generalized decreases in crayfish abundance throughout the river following restoration. More detailed observations of different reaches, however, indicates that fish species and density exert some regulation over crayfish numbers. Crayfish abundance decreased following restoration where exotic fishes remain but slightly increased in numbers where they were removed. Areas in the river with increased travertine deposition had the largest declines following restoration. These observations suggest that crayfish abundance in this system is limited by substrate modification by travertine and to a lesser extent by regulation of fish predation.