Brown Trout (Salmo trutta): A Technical Conservation Assessment Prepared for the USDA Forest Service, Rocky Mountain Region, Species Conservation Project April 26, 2007 Laura Belica1 with life cycle model by David McDonald, Ph.D.2 11623 Steele Street, Laramie Wyoming 82070 2Department of Zoology and Physiology, University of Wyoming, P.O. Box 3166, Laramie, WY 82071 Belica, L. (2007, April 26). Brown Trout (Salmo trutta): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/ browntrout.pdf [date of access]. ACKNOWLEDGMENTS I would like to thank the many biologists and managers from Colorado, Kansas, Nebraska, South Dakota, and Wyoming and from the national forests within Region 2 who provided information about brown trout populations in their jurisdictions. I also extend my appreciation to David B. McDonald at the University of Wyoming for the population demographic matrix analysis he provided. Thank you to Nathan P. Nibbelink for coordinating the cost- share agreement with the USDA Forest Service. I especially thank Richard Vacirca, Gary Patton, and David Winters of the USDA Forest Service for their help in bringing this report to completion. I thank Nancy McDonald and Kimberly Nguyen for their attention to detail in preparing this report for publication. Finally, I would like to thank Peter McHugh for graciously taking the time to review and comment on this assessment. AUTHOR’S BIOGRAPHY Laura A. T. Belica received a M.S. degree in Zoology and Physiology from the University of Wyoming in 2003 (as L.A. Thel). Her research interests center around the ecology of fishes, hydrology, and watershed management, especially as they relate to the management of aquatic ecosystems and native fishes. COVER PHOTO CREDIT Brown trout (Salmo trutta). Photograph taken by Eric Engbretson. Used with permission. 2 3 SUMMARY OF KEY COMPONENTS FOR CONSERVATION OF BROWN TROUT The brown trout (Salmo trutta) is native to Europe, North Africa, and West Asia, and since its introduction to North America in 1883, it is now found throughout southern Canada and much of the United States. Brown trout have been introduced into streams, rivers, reservoirs, and lakes and have been able to form self-sustaining populations in all of these environments. Non-native brown trout are thought to have replaced native inland cutthroat trout (Oncorhynchus clarki) in parts of their range, particularly in large rivers and lakes. Within the Rocky Mountain Region (Region 2) of the USDA Forest Service (USFS), brown trout are found in Colorado, Kansas, Nebraska, South Dakota and Wyoming, but are most widespread in Colorado and Wyoming. In those states of Region 2 where they occur, except for Kansas, brown trout are found in public waters providing recreational fisheries, including on many federal lands, such as several National Forest System, National Park System, and Bureau of Land Management lands. Water management activities that alter stream flow during spawning and the sensitive early life stages can adversely affect naturalized brown trout populations. Land management practices may also degrade or reduce habitat and negatively affect populations. Fisheries management activities applied to brown trout are mostly designed to maintain or improve recreational trout fisheries. However, in areas where the preservation or restoration of native fish populations is a primary goal, removal of brown trout may be a component of native species recovery efforts. Brown trout tolerate annual fluctuations in fertility, but populations are sensitive to changes in absolute survivorship of young-of-year and changes in relative proportions of the younger age-classes in the population. If conditions that lower brown trout yearling recruitment or change the proportion of age-0 through age-2 fish in a population are sustained over several years, population age-structure, size, and biomass may be altered. 2 3 TABLE OF CONTENTS ACKNOWLEDGMENTS ..............................................................................................................................................2 AUTHOR’S BIOGRAPHY............................................................................................................................................2 COVER PHOTO CREDIT .............................................................................................................................................2 SUMMARY OF KEY COMPONENTS FOR CONSERVATION OF BROWN TROUT .............................................3 LIST OF TABLES AND FIGURES ...............................................................................................................................6 INTRODUCTION ..........................................................................................................................................................7 Goal............................................................................................................................................................................7 Scope, Uncertainty, and Limitations ..........................................................................................................................7 Web Publication and Peer Review .............................................................................................................................9 MANAGEMENT STATUS AND NATURAL HISTORY .............................................................................................9 Management Status and Existing Regulatory Mechanisms.......................................................................................9 USDA Forest Service ............................................................................................................................................9 State agencies ........................................................................................................................................................9 Biology and Ecology................................................................................................................................................10 Description and systematics................................................................................................................................10 Taxonomy .......................................................................................................................................................10 Identification...................................................................................................................................................11 Distribution and abundance.................................................................................................................................12 Range..............................................................................................................................................................12 Abundance and population trends ..................................................................................................................16 Activity and movement patterns .........................................................................................................................19 Social patterns for spacing..............................................................................................................................20 Diel activity patterns and behavior.................................................................................................................21 Movement patterns .........................................................................................................................................25 Patterns of dispersal of young and adults.......................................................................................................28 Habitat .................................................................................................................................................................29 Habitat use - streams and rivers......................................................................................................................30 Habitat use - reservoirs and lakes...................................................................................................................33 Spawning habitat ............................................................................................................................................34 Winter habitat use - streams and rivers...........................................................................................................35 Young-of-year habitat use...............................................................................................................................36 Juvenile habitat use.........................................................................................................................................40 Food habits ..........................................................................................................................................................41 Breeding biology.................................................................................................................................................45 Spawning season ............................................................................................................................................47 Incubation period............................................................................................................................................47