Impacts of harbour seals on Chinook and coho salmon in the Strait of Georgia
Presentation Abstract
Historically, Chinook and coho were two of the most valuable commercial and recreational salmon species in western North America, particularly in the Salish Sea. However, marine survival rates of these species have declined dramatically since the 1970s as numbers of harbour seals increased. This correlation has led some scientists to hypothesize that seal predation may be impeding the recovery of Chinook and coho salmon, primarily because reduced exploitation rates over past decades have not returned them to historic abundances. While seal consumption of adult salmon has been quantified in past studies, few attempts have been made to estimate predation on out-migrating smolts. Most existing estimates of predation on juveniles are based on the presence/absence of hard structures in seal fecal material, which cannot determine salmon species and are susceptible to biases associated with survival of diagnostic hard structures during the digestion process. Here, DNA-based diet data is combined with several modeling approaches to estimate annual seal consumption of juvenile salmon in the Strait of Georgia. Results suggest that seal predation on juvenile Chinook and coho may be responsible for up to half of the total natural mortality experienced by these species during the early marine stage. Estimates of mortality from this analysis will inform predator-prey models that could be used to test alternative management strategies that may facilitate recovery of key populations of salmon.
Session Title
The Salish Sea Marine Survival Project- Novel Approaches, Project Status and Key Findings
Conference Track
Species and Food Webs
Conference Name
Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)
Document Type
Event
Start Date
2016 12:00 AM
End Date
2016 12:00 AM
Location
2016SSEC
Type of Presentation
Oral
Genre/Form
conference proceedings; presentations (communicative events)
Contributing Repository
Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.
Subjects – Topical (LCSH)
Harbor seal--Food--Georgia, Strait of (B.C. and Wash.); Harbor seal--Behavior--Georgia, Strait of (B.C. and Wash.); Chinook salmon--Effect of predation on--Georgia, Strait of (B.C. and Wash.); Coho salmon--Effect of predation on--Georgia, Strait of (B.C. and Wash.)
Geographic Coverage
Salish Sea (B.C. and Wash.); Georgia, Strait of (B.C. and Wash.)
Rights
This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.
Type
Text
Language
English
Format
application/pdf
Impacts of harbour seals on Chinook and coho salmon in the Strait of Georgia
2016SSEC
Historically, Chinook and coho were two of the most valuable commercial and recreational salmon species in western North America, particularly in the Salish Sea. However, marine survival rates of these species have declined dramatically since the 1970s as numbers of harbour seals increased. This correlation has led some scientists to hypothesize that seal predation may be impeding the recovery of Chinook and coho salmon, primarily because reduced exploitation rates over past decades have not returned them to historic abundances. While seal consumption of adult salmon has been quantified in past studies, few attempts have been made to estimate predation on out-migrating smolts. Most existing estimates of predation on juveniles are based on the presence/absence of hard structures in seal fecal material, which cannot determine salmon species and are susceptible to biases associated with survival of diagnostic hard structures during the digestion process. Here, DNA-based diet data is combined with several modeling approaches to estimate annual seal consumption of juvenile salmon in the Strait of Georgia. Results suggest that seal predation on juvenile Chinook and coho may be responsible for up to half of the total natural mortality experienced by these species during the early marine stage. Estimates of mortality from this analysis will inform predator-prey models that could be used to test alternative management strategies that may facilitate recovery of key populations of salmon.
