A Study of the Spawning Ecology and Early Life History Survival of Bonneville Cutthroat Trout

Abstract

We completed a large-scale field experiment in four tributaries of the Logan River, Utah, where the largest metapopulation of imperiled Bonneville cutthroat trout Oncorhynchus clarkii utah persists. We documented the spatial and temporal distributions of spawners, quantified substrate use versus substrate availability, and evaluated differences in hatch and emergence fry success between and among sites in relation to habitat characteristics. We observed considerable variability in the timing, magnitude, and duration of spawning among study areas (streams), in part as a function of a variable, multipeaked hydrograph. Nevertheless, across study areas, >70% of redds were constructed on the final descending limb of the hydrograph. Despite large differences in the amount of spawning substrate available, Bonneville cutthroat trout utilized a narrow range of substrate and sizes (3–80 mm) similar to that utilized by other subspecies of cutthroat trout, albeit biased towards larger sizes. Water temperatures generally remained below the recommended range (6–17°C) for spawning; however, the viability of this metapopulation of cutthroat trout suggests that the recommended temperature range for spawning is overestimated for this subspecies and (or) does not account for local thermal adaptation. Hatch varied from 43% to 77% and emergence survival from 39% to 65% among streams, and within-stream variability was substantial; both survival rates declined significantly as a function of increased fine sediment concentrations. Egg development rates were nearly 50% greater in a high-elevation tributary where redd counts were also lowest. In high, mountain systems with short growing seasons, this incubation delay likely presents a significant growth disadvantage for age-0 trout. Our research enhances our understanding of Bonneville cutthroat trout spawning ecology and early survival and provides critical information for aiding in the development of benchmarks for their recovery. Effective conservation efforts should be directed towards minimizing anthropogenic activities that result in excess sedimentation in their critical spawning tributaries.

Received April 15, 2011; accepted February 7, 2012

ACKNOWLEDGMENTS

This research was primarily funded by the U.S. Forest Service, Utah Division of Wildlife Resources, Project XII, Sport Fisheries Research, Grant Number F-47-R, Segment 20 and in-kind support from the U.S. Geological Survey, Utah Cooperative Fish and Wildlife Research Unit. Special thanks to Gary Thiede for providing technical advice and logistical oversight of our field crews, and graduate students in the Fish Ecology Laboratory at Utah State University. Susan Durham provided statistical advice and assistance and Christy Meredith assisted with GIS and graphical issues. We would also like to thank David Koons and Jeremiah Wood for intellectual and field contributions; a long list of seasonal technicians also assisted with field work. Any use of trade product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.