Quantifying impacts of harbor seal predation on Puget Sound salmon

Investigator: Ben Nelson

This study integrates harbor seal diet data and novel modeling approaches to determine how many Chinook and coho salmon are lost to harbor seal predation in Puget Sound each year. Recent partnering studies in the Strait of Georgia suggest that harbor seals may target juvenile Chinook and coho in the early marine stage. While Chinook and coho juveniles comprise a small fraction of the average seal diet, harbor seals’ considerable energetic requirements and high abundances in the Salish Sea may result in significant predation on juvenile salmon.

Researchers are constructing models which incorporate observed seal diet data, bioenergetic requirements of Puget Sound harbor seals, growth and natural mortality rates of salmon, production estimates of hatchery and natural-origin salmon, and abundance estimates of harbor seals. These models allow researchers to estimate the annual consumption of both juvenile and adult Chinook and coho salmon by harbor seals in Puget Sound, calculate the fraction of the total population lost to seal predation, determine what percentage of overall natural mortality is due to harbor seal predation, and assess spatial variation in predation rates throughout Puget Sound. Additionally, researchers can infer whether and how harbor seal predation rates have changed since the 1970s.