Temperature-Not Flow-Predicts Native Fish Reproduction with Implications for Climate Change

Habitat alterations and introduction of nonnative fishes reduced the distributions of the Flannelmouth Sucker Catostomus latipinnis, Bluehead Sucker C. discobolus, and Roundtail Chub Gila robusta to less than 50% of their historical ranges. Climate change models generally predict decreased streamflows and increased water temperatures that may further affect these species. Understanding the effects of flow and water temperature on their life histories should lead to better assessments of climate change impacts on extant populations and more informed management for species conservation. Basinwide larval fish sampling and hatch dates derived from otolith daily increment counts showed that water temperature was the dominant environmental factor cueing reproduction in the upper White River basin, Colorado. Reproduction for all three species began in spring, occurring first at warmer, lower-elevation, downstream locations and progressing upriver to higher elevations as water temperatures increased. Warmer water temperatures in tributaries initiated earlier reproductive activity compared to adjacent cooler main-stem habitat. Presence of larvae in samples and estimated hatch dates demonstrated a distinct, predictable upstream progression of reproduction associated with warming water and clear upstream limits to reproduction for all three species. Larval presence and hatching dates revealed earlier reproductive activity in 2012 than in 2013, driven by lower flow and earlier stream warming. A regression model predicted stream temperature during fish spawning seasons under different climate change scenarios and showed expanded upstream limits of thermally suitable reproductive habitat and earlier reproduction for our study species. The long-term implications of climate change are unknown, but managers should strive to perpetuate the valuable and relatively pristine native fish community in the upper White River drainage as a vestige of those that formerly existed throughout the Colorado River basin.