Environmental and Population Strain Effects on Survival of Lahontan Cutthroat Trout in Walker Lake, Nevada: A Bayesian Approach

Abstract

Lahontan cutthroat trout Oncorhynchus clarkii henshawi are listed as threatened under the U.S. Endangered Species Act. Populations inhabiting terminal lakes in the Great Basin of Utah and adjacent states face increasing salinity associated with increased anthropogenic use of water and climate change. We used tag recovery models and Markov chain–Monte Carlo methods to assess models of variation in annual survival and tag recovery rates for two genetic strains (Pilot Peak and Pyramid Lake) of Lahontan cutthroat trout stocked into Walker Lake, Nevada, from 1998 to 2008. The best-performing model of annual survival and tag recoveries allowed recovery probability in the first year after release to differ from subsequent recovery rates. The best model contained an interaction between strain and total dissolved solids (TDS) for annual survival. That is, the annual survival of both strains declined as TDS increased, but the Pilot Peak strain was more sensitive to TDS than was the Pyramid Lake strain. The annual survival of fish from the Pilot Peak strain was higher than that of the Pyramid Lake strain at all but the highest TDS levels. Although TDS levels in 2005–2008 were too high to warrant continued stocking of cutthroat trout into Walker Lake, if flows into Walker Lake are increased sufficiently to return TDS levels to those of the late 1990s, the Pilot Peak strain should be stocked.

Received August 24, 2011; accepted February 6, 2012

ACKNOWLEDGMENTS

This work was funded by the Lahontan National Fish Hatchery Complex of the US Fish and Wildlife Service. Analysis was supported by the Nevada Agricultural Experiment Station. T. Anderson, J. Bigelow, D. Bloomquist, E. Culver, A. Donnell, G. Emm, R. Hinz, J. Hoang, E. Horgen, E. Kelly, B. Ladago, C. Luton, T. Loux, R. Peka, D. Rabbers, D. Schildt, J. Steele, P. Solberger, K. Tisdale, J. Vasquez, C. Williams, and K. Wright all assisted with field work. L. Heki enthusiastically supported the work administratively. C. Luton also assisted with data management. Animal handling procedures were approved by the University of Nevada Reno Institutional Animal Care and Use Committee: protocol number A07/08–15.