W. Carl Saunders Department of Watershed Science, Utah State University Phaedra Budy

1. Biotic resistance by native Bonneville cutthroat trout to the establishment of exotic brown trout is influenced by population density W. Carl Saunders Department of Watershed Science, Utah State University Phaedra Budy Department of Watershed Science, USGS Utah Cooperative Fish & Wildlife Research Unit Utah State University

2. Biological invasions restructure ecosystems • A leading cause of species declines • Advances identifying characteristics that facilitate invasion Biotic Invasions

3. Biological Invasions: invasion process Different factors • Limited understanding of failed invasions!

4. Area of Detail Salt Lake City UTAH N 0 2 4 6 8 1 0 Km Logan River: ongoing salmonid invasion

5. Long-Term Monitoring: trout distributions

6. Allopatric distribution • No migration barrier • Limited environmental resistance: • Competitively superior throughout drainage • Successfully spawn and rear Long-Term Monitoring: trout distributions

7. Biotic Resistance

8. Goals & Objectives • Management objective: • Restore Bonneville cutthroat trout in lower Logan River • Research objectives: • Test for evidence of Biotic Resistance by cutthroat trout • Identify densities sufficient to resist invasion

9. Biotic Resistance: Experimental Approach In-situ stream experiments Laboratory trials

10. Results of Previous Research • McHugh & Budy 2005, 2006 • Test CUTT, BROWN, CUTT * BROWN • Brown trout out-compete cutthroats at multiple scales and across altitudinal gradient • Brown trout perform better (experimentally) at high elevations

11. Biotic Resistance: laboratory trials • Small scale (4.5 m2) • 2 brown trout per tank • 150 – 300 mm • 4 cutthroat treatments • 3, 4, 5, 6 cutthroat per tank • 100 – 300 mm • Recorded fish behavior with HD cameras

12. Biotic Resistance: laboratory results

13. Biotic Resistance: laboratory results • Predation • Disease

14. Biotic Resistance: laboratory results

15. Biotic Resistance: laboratory results b b b a

16. Biotic Resistance: behavioral mechanism

17. Biotic Resistance: Experimental Approach In-situ stream experiments Laboratory trials

18. Biotic Resistance: in situ stream experiment • Intermediate scale (20 m long enclosures) • 0.1 brown trout per m2 • 150 – 300 mm • 4 cutthroat densities • 0.2, 0.3, 0.4, 0.6 fish per m2 • 100 – 300 mm

19. Biotic Resistance: in situ stream experiment

20. Biotic Resistance: in situ stream experiment b b b a

21. Conclusions • Brown trout unaffected by cutthroat density • Cutthroat do better at higher densities • Aggression as mechanism for competition • Management implications: • High density populations resist invasion • Factors that weaken populations may increase the species replacement through competition

22. Acknowledgements • UDWR: Paul Thompson, Craig Schaugaard, Chris Wilson, Dedicated hunter Program • Cache Anglers, TU:Paul Holden, Paul Burnett, ChaddVanZanten • USFS: Paul Chase, Brett Roper Fish Ecology Lab: Gary Thiede, Peter Mackinnon, Christy Meredith, Tracy Bowerman, Lisa Winters, Nick Heredia, Sam Mckay, Tim Walsworth, Stephen Klobucar, Wes Gordon, Konrad Hafen, Todd Wright, Jared Baker, Hannah Moore, Bryce Rolholt

23. Questions