Hydrological Disturbances Regimes and Their Impacts on Native and Non-Native Fish Communities in Aravaipa Canyon, Arizona

Aravaipa Creek is the preeminent native fish assemblages remaining in the Gila Basin and is home to three federally listed endangered or candidate fish species.   Hydrologic baseflow and periodic cyclonic and monsoonal flooding events are needed to ensure that (1) diversity and variability of aquatic habitats are maintained for the seven native fish species, and (2) populations of exotic species continue at low abundance or are eventually removed from the system.  Variability in flow is considered necessary for both the long term perseverance and survival of native fishes and the periodic extrication of exotic individuals from the system. Here we present data from a 50 year monitoring period for Aravaipa fishes that examines short and long-term variation in fish populations.  Native species show considerable variability in population abundance and there is a positive relationship between baseflow and native fish populations, but exotic fish populations do not show the same response.  After periodic flooding, populations of exotic species are, to a large extent, significantly reduced.  Variability is important for the persistence of the native fish populations. In contrast, lack of flow variability results in an increase in nonnative fishes.