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University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 2011 MANAGEMENT AND LIFE HISTORY CONSEQUENCES OF HYBRIDIZATION BETWEEN WESTSLOPE CUTTHROAT TROUT (ONCORHYNCHUS CLARKII LEWISI) AND RAINBOW TROUT (ONCORHYNCHUS MYKISS) Matthew Philip Corsi The University of Montana Follow this and additional works at: https://scholarworks.umt.edu/etd Let us know how access to this document benefits ou.y Recommended Citation Corsi, Matthew Philip, "MANAGEMENT AND LIFE HISTORY CONSEQUENCES OF HYBRIDIZATION BETWEEN WESTSLOPE CUTTHROAT TROUT (ONCORHYNCHUS CLARKII LEWISI) AND RAINBOW TROUT (ONCORHYNCHUS MYKISS)" (2011). Graduate Student Theses, Dissertations, & Professional Papers. 640. https://scholarworks.umt.edu/etd/640 This Dissertation is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. MANAGEMENT AND LIFE HISTORY CONSEQUENCES OF HYBRIDIZATION BETWEEN WESTSLOPE CUTTHROAT TROUT (ONCORHYNCHUS CLARKII LEWISI) AND RAINBOW TROUT (ONCORHYNCHUS MYKISS) By MATTHEW PHILIP CORSI B.S. IN FISHERIES RESOURCES MANAGEMENT, UNIVERSITY OF IDAHO, MOSCOW, IDAHO, 2003 Dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Fish and Wildlife Biology The University of Montana Missoula, MT Fall 2011 Approved by: Stephen Sprang, Associate Provost for Graduate Education Graduate School Lisa Eby, Chair Wildlife Biology Fred Allendorf Wildlife Biology Winsor Lowe Division of Biological Sciences Bruce Rieman U.S. Forest Service Rocky Mountain Research Station Paul Spruell Southern Utah University ABSTRACT Corsi, Matthew P., Ph. D., Fall 2011 Fish and Wildlife Biology Management and life history consequences of hybridization between westslope cutthroat trout (Oncorhynchus clarkii lewisi) and rainbow trout (Oncorhynchus mykiss) Chairperson: Dr. Lisa Eby The role of introductions of nonnative fishes in the decline of native fishes cannot be overstated. Westslope cutthroat trout (Oncorhynchus clarkii lewisi, WCT) are a salmonid native to the northern Rocky Mountains. These trout hybridize with rainbow trout (O. mykiss, RBT) where they are sympatric; however, in portions of the WCT range where RBT have been introduced, hybridization appears to spread rapidly and threatens continued existence of WCT. The conservation value of these hybridized populations is equivocal, and a better knowledge of the ecological, demographic, behavioral, and genetic consequences of hybridization is needed to better inform conservation strategies. I investigated three related questions: specifically, what landscape factors are associated with estimates of introgression; what are life history differences between WCT and hybrids; and what are tradeoffs in restoring migratory life history in populations threatened by hybridization? The riverscape context plays a substantial role in the distribution of hybrids, as estimates of introgression declined with increases in stream slope, elevation, and distance from a primary source of RBT, three correlated landscape variables. Spatial variation in patterns of hybridization suggests clarifying objectives for sampling and careful designs are necessary to adequately understand the status of populations. Variation in location may relate to some of the ecological differences, such as growth, among fish with different levels of introgression. In the Jocko River, hybrids with ancestry > 20% RBT demonstrated higher growth, earlier migration, increased egg size, and lower fecundity versus WCT. These lines of evidence demonstrate the importance of limiting further hybridization even in populations that already have low levels of hybridization. Given that many unaltered populations currently reside in isolated habitat fragments, I evaluated several demographic tradeoffs of restoring a migratory life history weighed against the risks of increased potential for hybridization from removing barriers or selectively passing migratory fish above the barriers using both matrix and genetic population models. Restoration of migratory life history substantially increases population viability; however, hybridization in above-barrier population increases predictably relative to hybridization status of below-barrier population, which may reduce viability if vital rates are reduced in hybrids. Hybridization creates a challenging set of management problems, but this research adds several important pieces to the puzzles to help develop and evaluate conservation strategies. ii ACKNOWLEDGEMENTS There are many people and organizations that helped me in this great graduate school adventure. First, I would like to thank my major advisor, Dr. Lisa Eby, whose ability to inspire her students stems from her undying curiosity, her unmatched energy, and her exceptional intelligence. Whenever I had hit a low point, a meeting with Lisa always made science, my project, and graduate school fun again. I also want to thank Dr. Paul Spruell, who, before he left for the sunny canyons of Southern Utah, was my first major professor. Paul accepted me as a student at the University of Montana, and was most influential in my realization that science, as well as fisheries management, are efforts of creativity. I have deep respect for Lisa and Paul as mentors, but I am also glad to consider them friends. Craig Barfoot, a fisheries biologist for the Confederated Salish and Kootenai Tribes, made sure that I had a successful dissertation project by ensuring that I had funding, samples, field support, and understanding of the natural history of the Jocko River. Craig is an outstanding biologist with exceptional energy and curiosity, and I enjoyed all of the hundreds of phone conversations he and I shared talking about cutthroat trout and hybrids in the Jocko River, fine cuisine, and good literature. I would like to thank my committee, Dr. Fred Allendorf, Dr. Winsor Lowe, and Dr. Bruce Rieman. All three found various ways to force me to stretch myself academically. I would like to especially thank Bruce, because the conversations I had with him while I was working on my proposal and studying for comprehensive exams iii gave me much of the knowledge and confidence I needed to know that I am a capable fisheries biologist. I received funding for this project from a variety of sources, but primarily from the Confederated Salish and Kootenai Tribes, who asked me to answer a simple management question, but gave me the flexibility and support to turn it into a dissertation. I would also like to thank the National Fish and Wildlife Foundation, NSF GK-12, the Montana Water Center, the Sustainable Fisheries Foundation, the Westslope Chapter of Trout Unlimited, the Montana Chapter of the American Fisheries Society, and the Cirica family for financial support. The friendship and support of the faculty and staff of the Wildlife Biology Program, many graduate students, and laboratory technicians with whom I shared many cups of coffee, glasses of beer, and many, many laughs, made Missoula my home. I would especially like to thank Steve Amish and Sally Painter for sharing their home and family with me. Aubree Benson, Magnus and Rebecca McCaffery, Olga Helmy, Kellie Carim, and Leslie Nyce gave me endless support on academic and personal levels, and they made the Eby Lab a force to be reckoned with in the fields of aquatic ecology in the State of Montana. Angela Lodmell, Willa Fouts, and Maria Naccarato made my project possible with their assistance in the lab. I would like to give special thanks to Jason Tack, an excellent individual who always helped me remember what life is really all about. I could not have survived without the friendship and brotherhood of John Henry Powell III, who has been my sounding board for all things scientific and personal from my very first day of graduate school. iv I finished my final years of graduate school from a home office in the fair state capital, Helena. I would like to thank Paul and Lisa Kusnierz, Stephen Fernandes, Jessie Frazier, and Shane Castle for their friendship and support in making Helena a home. Finally, I would like to thank my family. My father and mother, Chip and Diane Corsi, and my sister, Meghan Corsi gave me endless love and support while I completed this adventure. My Dad introduced me to the joys of streams, fish, and fishing, and he has, and always will be, my best fishing and hunting partner. Erin West and I have shared many fond memories in the taverns, pubs, and streets of Missoula. Marcia Spiegel, my tenacious and beautiful grandmother showed me the importance of courage and grace during the time we shared in Missoula. I would also like to thank Aldo, my ever-present companion who passed away as I was finishing this dissertation. Lastly, I would like to thank my wife, Emily, who I would not have met if I hadn’t been a doctoral student and is, therefore, the best possible reason for joining the Ph.D. program in Wildife Biology. She is a truly remarkable and beautiful person with an astonishing capacity for love, patience, and support. I thank her for being my very best friend. v TABLE OF CONTENTS ABSTRACT ........................................................................................................................ ii ACKNOWLEDGEMENTS

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