Rainbow Trout (Oncorhynchus mykiss): A Technical Conservation Assessment Prepared for the USDA Forest Service, Rocky Mountain Region, Species Conservation Project October 10, 2008 W. Linn Montgomery1 and Yael Bernstein1,2 1 Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011-5640 2 SWCA Environmental Consultants, 114 N. San Francisco St. #100, Flagstaff, AZ 86001 Peer Review Administered by American Fisheries Society Bernstein, Y. and W.L. Montgomery. (2008, October 10) Rainbow Trout (Oncorhynchus mykiss; Walbaum, 1792): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/rainbowtrout.pdf [date of access]. ACKNOWLEDGMENTS We thank Richard Vacirca, Gary Patton, and David Winters of the USDA Forest Service Rocky Mountain Region for the opportunity to prepare this assessment and for their assistance at many points in its preparation and finalization. Thanks are also due an anonymous reviewer for many helpful comments. AUTHORS’ BIOGRAPHIES W. Linn Montgomery received B.A., M.A., and Ph.D. degrees from the UC Berkeley, UCLA, and Arizona State University, respectively. As a postdoctoral researcher with Woods Hole Oceanographic Institution, he studied the ecology of Atlantic salmon and sea-run brook trout in eastern Quebec before joining the faculty at Northern Arizona University. From 1984 to 1987, he served on, and in 1986 chaired, the Arizona Game and Fish Commission. He also served as Commission representative to the Arizona Water Quality Control Council and various committees of the Western Association of Fish and Wildlife Agencies. His students have studied rainbow trout, Atlantic salmon, tilapia, native and exotic cyprinids, marine surgeonfishes, damselfishes and scorpionfishes, rattlesnakes, ephemeral pond crustaceans, crayfish, river ecology, and fish paleontology. His personal research interests focus on feeding ecology and physiology of herbivorous fishes, including work on their lipid dynamics and gut microbes, and reproductive ecology of salmonids and marine reef fishes. Yael Anna Bernstein received B.S. degrees in both Microbiology (with a Minor in Chemistry) and Finance and Computer Information Systems from Northern Arizona University; she has completed portions of a Masters degree program in Biology with an aquatic ecology focus. She has 11 years of experience with scientific monitoring and research trips in Grand Canyon, and she has worked for Northern Arizona University as a cooperator with the Grand Canyon Monitoring and Research Center from 2002 to 2005. She has direct experience with issues related to native and nonnative fish studies in the Southwest and is experienced in field sampling techniques, data analysis, and laboratory analyses, including food studies and otolith work. COVER PHOTO CREDIT Photograph of rainbow trout (Oncorhynchus mykiss) by E.R. Keeley, used with permission. 2 3 SUMMARY OF KEY COMPONENTS FOR CONSERVATION OF THE RAINBOW TROUT Status The Rocky Mountain Region (Region 2) of the USDA Forest Service is beyond the native range of the rainbow trout (Oncorhynchus mykiss). Populations in Region 2 were established by introductions from hatcheries for recreation and market purposes, and it is not considered a federally or state threatened, endangered, or sensitive species (U.S. Fish and Wildlife Service; http://endangered.fws.gov/). Elsewhere in its native range, several populations of rainbow trout are federally listed as threatened or endangered. However, this is not likely to influence the status of populations in Region 2, where the species is common in streams and lakes and populations are maintained either through self-sustaining natural reproduction or through various levels of supplemental stocking of hatchery fish where self- sustaining populations do not occur. Natural or anthropogenic alteration of habitat may lead to declines in individual populations, as may changes in management practices intended to protect native species; otherwise, the rainbow trout should be considered secure within Region 2. Primary Threats As noted above, there are no native stocks of rainbow trout in Region 2. Nonetheless, existing stocks in the Region face the potential for population declines under the influence of both natural and human threats that alter or destroy habitat. Addressed more specifically elsewhere in this assessment, these threats include, but are not limited to, reduction of stream discharge, and changes in water temperature, water quality, substrate, and food base. In addition, perpetuation of some existing populations and future development of new populations to support fishing demand will take place against a backdrop of concerns over conservation or recovery of native fishes and their habitats, which are documented in other assessments in this series. Such constraint was not in place when many of the existing rainbow trout populations were established. Primary Management Elements, Implications and Considerations Rainbow trout in the Rocky Mountain Region are an introduced, nonnative species capable of occupying a wide array of habitats, feeding on virtually any type of nutritionally valuable organism, and hybridizing with native trout that may be the focus of recovery efforts. This ecological flexibility has allowed them to join native faunas throughout the United States and the world, where they often alter relationships among members of the receiving fauna. Persistence of rainbow trout populations in Region 2 will depend on persistence of water quality and quantity sufficient to maintain the existing coolwater ecosystems they presently occupy. Populations presently maintained by stocking of catchable-size trout (in support of a “put-and-take” management strategy) or fingerlings (for a “put-grow- take” strategy) could be enhanced by providing additional spawning, fry, or juvenile habitat. Such actions could also reduce management costs by shifting the age and size of stocked fish toward earlier life history stages or by relying more on natural spawning. 2 3 TABLE OF CONTENTS ACKNOWLEDGMENTS ..............................................................................................................................................2 AUTHORS’ BIOGRAPHIES .........................................................................................................................................2 COVER PHOTO CREDIT .............................................................................................................................................2 SUMMARY OF KEY COMPONENTS FOR CONSERVATION OF THE RAINBOW TROUT ................................3 Status..........................................................................................................................................................................3 Primary Threats..........................................................................................................................................................3 Primary Management Elements, Implications and Considerations ...........................................................................3 LIST OF TABLES AND FIGURES ...............................................................................................................................6 INTRODUCTION ..........................................................................................................................................................7 Goal............................................................................................................................................................................7 Scope..........................................................................................................................................................................7 Treatment of Uncertainty ...........................................................................................................................................8 Application and Interpretation Limits of This Assessment........................................................................................8 Web Publication .........................................................................................................................................................9 Peer Review ...............................................................................................................................................................9 MANAGEMENT STATUS AND NATURAL HISTORY .............................................................................................9 Existing Regulatory Mechanisms, Management Plans, and Conservation Strategies...............................................9 Biology and Ecology................................................................................................................................................16 Systematics..........................................................................................................................................................16 Species description..............................................................................................................................................18 Salmonid life history characteristics ..............................................................................................................18 Distribution and abundance.................................................................................................................................19