Incorporating Movement Patterns to Improve Survival Estimates for Juvenile Bull Trout

Abstract

Populations of many fish species are sensitive to changes in vital rates during early life stages, but our understanding of the factors affecting growth, survival, and movement patterns is often extremely limited for juvenile fish. These critical information gaps are particularly evident for bull trout Salvelinus confluentus, a threatened Pacific Northwest char. We combined several active and passive mark–recapture and resight techniques to assess migration rates and estimate survival for juvenile bull trout (70–170 mm total length). We evaluated the relative performance of multiple survival estimation techniques by comparing results from a common Cormack–Jolly–Seber (CJS) model, the less widely used Barker model, and a simple return rate (an index of survival). Juvenile bull trout of all sizes emigrated from their natal habitat throughout the year, and thereafter migrated up to 50 km downstream. With the CJS model, high emigration rates led to an extreme underestimate of apparent survival, a combined estimate of site fidelity and survival. In contrast, the Barker model, which allows survival and emigration to be modeled as separate parameters, produced estimates of survival that were much less biased than the return rate. Estimates of age-class-specific annual survival from the Barker model based on all available data were 0.218±0.028 (estimate±SE) for age-1 bull trout and 0.231±0.065 for age-2 bull trout. This research demonstrates the importance of incorporating movement patterns into survival analyses, and we provide one of the first field-based estimates of juvenile bull trout annual survival in relatively pristine rearing conditions. These estimates can provide a baseline for comparison with future studies in more impacted systems and will help managers develop reliable stage-structured population models to evaluate future recovery strategies.

Received February 1, 2012; accepted July 31, 2012

ACKNOWLEDGMENTS

Funding for this project was provided by the U.S. Fish and Wildlife Service, Columbia River Fisheries Program Office; the U.S. Geological Survey, Utah Cooperative Fish and Wildlife Research Unit (in kind); and the Ecology Center at Utah State University (USU). Additional support was provided by the USU Vice-Presidential Fellowship and the Seeley–Hinckley Scholarship, both awarded to T. Bowerman. This paper was improved by reviews of previous drafts by Carl Saunders, Mary Conner, Charles Hawkins, and Joseph Wheaton. Expert advice was provided by Howard Schaller, David Koons, and Robert Al-Chokhachy. Logistical support was provided by Peter MacKinnon, Gary Thiede, John Ehart, George Ehmer, and Dwayne Wright. Field data were collected with assistance from M. Todd, R. Carpen, M. Mustin, M. Schifiliti, G. Hill, M. Archibald, A. Dean, W. Kern, R. Al-Chokhachy, A. Hill, B. Simcox, S. Petre, L. Tennant, S. Rizza, and C. Cahill. We thank Phil Howell, Paul Sankovich, Courtney Newlon, Don Anglin, Darren Gallion, Ryan Koch, Marshall Barrows, David Hines, William Duke, and the Fish Ecology Lab at USU for providing data and support. This study was performed under the auspices of Utah State University protocol 1082. The use of trade names or products does not constitute endorsement by the U.S. Government.