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Evaluation of Avian Predation on
Juvenile Salmonids
in the Columbia River Estuary
Donald E. Lyons
Ph.D. Candidate
Oregon State University
Department of Fisheries and Wildlife
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
Objective
Estimate smolt mortality due to tern and cormorant predation
Methodology
Demand-based bioenergetics estimates of fish consumption
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
Caspian Tern
Management Chronology
1999-2000
Relocation
2001-2007
East Sand Island
1987-1998
Rice Island
Many Marine
Fish Nearby
Few Marine
Fish Nearby
2008-2012? Dispersal of ~60% of estuary population
Rice Is.
East Sand Is.
Salmonid Mortality Rates due to Tern Predation
1997-2006
1997-1999
2000-2006
All Salmonids
4.8 - 10.3
3.2 - 5.5
Coho
13.7 - 19.6
6.1 - 12.4
Sub-yearling Chinook
2.6 - 10.9
0.6 - 1.8
Yearling Chinook
2.8 - 6.9
Steelhead
7.4 - 12.2
Salmonid Mortality Rates (%) due to Tern Predation:
Anticipated Improvements due to Tern Dispersal
1997-1999
2000-2006
Anticipated
All Salmonids
4.8 - 10.3
3.2 - 5.5
2.0
Coho
13.7 - 19.6
6.1 - 12.4
3.6
Sub-yearling Chinook
2.6 - 10.9
0.6 - 1.8
0.4
Yearling Chinook
2.8 - 6.9
1.9
Steelhead
7.4 - 12.2
3.7
Cormorant and Tern Comparison
Tern
Cormorant
Numbers (2006)
18,400
27,500
Population Trend
Stable
Increasing
650
2500
% Salmon in Diet
17 – 47
2 – 25
Chicks Raised per Pair
0.4 – 1.4
1.2 – 2.1
April – mid August
April - September
Size (g)
Present in Estuary
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