Environmental drivers of growth of an endangered desert fish in two contrasting environments

Authors: Maria C.* Dzul, Charles B. Yackulic

Year: 2015 (xlvii)

Abstract

For fish species where survival is closely linked to body size, growth rates can play an important role in population dynamics. Determining environmental drivers and estimating responses of growth in such species can inform decision-making about conservation and management of imperiled species. We present a Bayesian growth model that uses monthly means of environmental covariates to describe subadult growth of endangered humpback chub Gila cypha in two contrasting environments, the Colorado River (CR) in Grand Canyon and the lower Little Colorado River (LCR). While the thermal and hydrologic regimes in the LCR are mainly influenced by air temperatures and precipitation patterns, respectively, the thermal and hydrologic regimes of the CR are influenced primarily by operations and reservoir level of Glen Canyon Dam and are therefore more seasonally constant. We compared models with food availability, turbidity duration, hydropeaking (CR only), and temperature effects in a model selection framework. Results indicated environmental influences on growth differed in the two habitats. While warmer temperatures were associated with increased growth in both systems, the effect was much stronger in the CR than the LCR. Furthermore, turbidity positively affected growth in the CR, and food availability positively affected growth in the LCR. Overall, environmental covariates explained more variation in growth in the CR than the LCR. A better understanding of how environmental covariates affect growth in the CR and LCR may improve the predictive capability of humpback chub population models and help predict how chub vital rates will change if the southwestern U.S. warms and becomes more arid in future years due to climate change.