Development of a Temperature-Dependent Growth Model for the Endangered Humpback Chub Using Capture-Recapture Data

Abstract

Model derived predictions of fish growth are frequently required for detailed investigations of population dy- namics to inform management decisions. Simple growth models are typically fit to paired age and length data, but age data is often not available from endangered species because of restrictions on lethal or invasive sampling methods. Growth increment data from capture-recapture studies can be used to inform such models, but currently available methods to fit data to growth models may produce biased predictions when growth is variable among individual fish, or when growth rate varies non-linearly with fish size. This study used a recently proposed growth model derived from basic bio- energetic principals to estimate growth of humpback chub in Grand Canyon, Arizona. The modeling framework allows incorporation of temperature-dependent shifts in growth rate associated with both seasonal variability in water tempera- ture and ontogenetic migrations between the seasonally warm Little Colorado River and the constantly cold Colorado River. Results indicate that consideration of temperature-dependent shifts in growth rate are critical to accurately describe the growth of humpback chub, and that management actions aimed at increasing water temperature in the thermally modi- fied Colorado River could aid the recovery of this species by increasing growth rate and survivorship.