Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8416
Title: Predator-prey interactions between harbor seals and migrating steelhead smolts revealed by acoustic telemetry
Author: B. A. Berejikian, M. E. Moore, Steven J. Jeffries
Publication Year: 2016
Journal: Marine Ecology Progress Series
Volume: 543
Pages: 21-35
DOI: 10.3354/meps11579
Keywords: harbor seals,Puget Sound,predation,steelhead,acoustic telemetry,

Changes in the Puget Sound ecosystem over the past 3 decades include increases in
harbor seal (Phoca vitulina) abundance and declines in many of their preferred prey species.
Harbor seals were outfitted with acoustic telemetry receivers and GPS tags to investigate spatial
and temporal interactions with steelhead trout Oncorhynchus mykiss smolts implanted with
acoustic transmitters. A total of 6846 tag detections from 44 different steelhead trout smolts (from
an initial group of 246 smolts released into 2 rivers) were recorded by the 11 recovered sealmounted
receivers. Central Puget Sound seal receivers detected a greater proportion of smolts
surviving to the vicinity of the haul-out locations (29 of 51; 58%) than Admiralty Inlet seal
receivers (7 of 50; 14%; p < 0.001). Detection data suggest that none of the tagged smolts were
consumed by the 11 monitored seals. Nine smolts were likely consumed by non-tagged harbor
seals based partly on detections of stationary tags at the seal capture haul-outs, although tag
deposition by other predators cannot be ruled out. Smolts implanted with continuously pinging
tags and smolts implanted with tags that were silent for the first 10 d after release were detected
in similar proportions leaving Puget Sound (95% CI for the difference between proportions:
−0.105 to 0.077) and stationary at harbor seal haul-outs (95% CI: −0.073 to 0.080). This study suggests
that harbor seals contribute to mortality of migrating steelhead smolts, and we hypothesize
that documented changes in the Puget Sound ecosystem may currently put steelhead smolts at
greater risk of predation by harbor seals and possibly other predators.


Characterizes spatio-temporal interactions between harbor seals and steelhead in Puget Sound and identifies areas where predation is evident.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.
Develop methods to use physiological, biological and behavioral information to predict population-level processes.