Population viability analysis of Chihuahua Chub in the Mimbres River, New Mexico

Abstract

ObjectiveThe Chihuahua Chub Gila nigrescens is a species of conservation concern throughout its distribution. The species is threatened by habitat degradation, nonnative species, and stochastic events (e.g., wildfire and drought). Although conservation efforts are ongoing, it is unclear how Chihuahua Chub in the Mimbres River, New Mexico, respond to conservation actions and stochastic events.MethodsTo address these uncertainties, we collected population demographic and dynamics data on Chihuahua Chub in the Mimbres River and used the data to construct an age‐structured, female‐based population model. The model was used to evaluate the response of Chihuahua Chub to (1) habitat improvement, (2) conservation stocking, and (3) stochastic events. Habitat improvements were modeled as a 50% increase in current abundance. Conservation stocking was represented by two stocking regimes: annual “maintenance” stocking of 200 fish or “catastrophe” stocking of 400–1500 fish for two consecutive years after a stochastic event. The effects of stochastic events were represented by 20–95% reductions in annual survival. Each scenario was simulated for 5000 iterations over 25 years.ResultIn the absence of conservation actions, the Chihuahua Chub population was projected to decline due to stochastic events. However, stocking and habitat improvement decreased the risk of extirpation. When stochastic events resulted in a 95% decline in annual survival, catastrophe stocking reduced population declines in abundance by 47–58% relative to no conservation stocking. When stochastic events caused a 20% reduction in annual survival, habitat improvement increased the median population size after 25 years by almost 50% relative to no habitat improvements.ConclusionCollectively, our results suggest that an increase in habitat and conservation stocking efforts is likely the most effective approach for conserving Chihuahua Chub in the face of future stochastic events.