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Evaluation of Avian Predation on Juvenile Salmonids in the Columbia River Estuary

This study evaluates the impact of avian (tern and cormorant) predation on juvenile salmon in the Columbia River Estuary. The objective is to estimate smolt mortality due to predation using demand-based bioenergetics estimates and complementary methodologies. The results show the benefits of tern relocation and suggest similar predation rates for cormorants, requiring further analysis.

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Evaluation of Avian Predation on Juvenile Salmonids in the Columbia River Estuary

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  1. Evaluation of Avian Predation on Juvenile Salmonidsin the Columbia River Estuary Donald E. Lyons Ph.D. Candidate Oregon State University Department of Fisheries and Wildlife

  2. Acknowledgments Oregon State University/USGS faculty and students: Dan Roby [PI], Jessica Adkins, Yasuko Suzuki, Lauren Reinalda, Nathan Hostetter RTR, Inc. colleagues: Ken Collis [Co-PI], Allen Evans, Mike Hawbecker NOAA Fisheries collaborators: Bob Emmett, Tom Good, Doug Marsh, Dick Ledgerwood, Scott Sebring, David Teel

  3. Objective Estimate smolt mortality due to tern and cormorant predation Methodology Demand-based bioenergetics estimates of fish consumption

  4. Complimentary Methodologies • PIT-Tag Based Predation Rates: • ESU or stock specific • Rearing or migration history, etc. can be examined • Number of fish available based on detections at upstream dam (Bonneville) • Bioenergetics Based Predation Rates: • Species specific – not ESU or stock • Number of fish available more difficult to estimate, but possible • Not subject to tagging sampling bias • Not subject to possible deleterious effects of tags

  5. Caspian Tern Management Chronology 1999-2000 Relocation 2001-2007 East Sand Island Many Marine Fish Nearby 1987-1998 Rice Island Few Marine Fish Nearby 2008-2012? Dispersal of ~60% of estuary population

  6. Rice Is. East Sand Is.

  7. Salmonid Mortality Rates due to Tern Predation1997-2006

  8. Salmonid Mortality Rates (%) due to Tern Predation:Anticipated Improvements due to Tern Dispersal

  9. Cormorant and Tern Comparison

  10. Conclusions • Tern relocation to East Sand Island benefited sub-yearling chinook and apparently coho • Planned dispersal of terns away from estuary provides some benefit for steelhead and coho, less for yearling chinook, little for sub-yearling chinook • Preliminary cormorant results suggest similar predation rates to terns, perhaps more impacts for sub-yearling chinook • Further cormorant work required to verify preliminary results, allow NEPA analysis

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