Presentation Abstract

Marine survival of steelhead smolts during their two week migration from river mouths to the Strait of Juan de Fuca has been estimated at 20% or less for several populations originating in Puget Sound. Low survival rates likely reduce overall smolt-to-adult return rates and limit recovery of Puget Sound steelhead populations. Harbor seals are generalist predators known to eat juvenile salmon in the Salish Sea. Harbor seals were captured in 2014 (12 seals) and 2016 (16 seals) and outfitted with acoustic telemetry receivers and GPS tags to quantify likely predation events and estimate foraging area overlap with acoustically tagged steelhead smolts. In 2014, mark-recapture estimates indicated that survival of steelhead through Central Puget Sound (Tacoma Narrows to Admiralty Inlet) was low (19%) and stationary tags were detected at harbor seal haulouts. In 2016 survival of steelhead through Central Puget Sound was high (69%), and no steelhead tags were detected stationary at harbor seal haulouts in the same region. However, in 2016, evidence of predation by harbor seals increased in the Nisqually estuary. Further, in both years, detection patterns of some tags were consistent with harbor seal movements, suggesting that tagged smolts had been eaten and were being carried by harbor seals. Steelhead smolt migratory behavior patterns through the Puget Sound epi-pelagic environment were very similar in the two years and do not likely explain the differences in survival or predation risk. We are currently exploring whether the increased presence of transient killer whales in Puget Sound and increases in anchovy abundance (an alternative prey source) may play a role in altering predation pressures and marine survival of steelhead smolts.

Session Title

The Salish Sea Marine Survival Project: Bottom-up and Top-down Processes

Keywords

Predation, Harbor seals, Steelhead, Top-down, Bottom-up

Conference Track

SSE11: Species and Food Webs

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE11-525

Start Date

6-4-2018 9:15 AM

End Date

6-4-2018 9:30 AM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (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

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Apr 6th, 9:15 AM Apr 6th, 9:30 AM

Interannual variation in early marine survival patterns of Puget Sound steelhead smolts indicates shifting predation pressures

Marine survival of steelhead smolts during their two week migration from river mouths to the Strait of Juan de Fuca has been estimated at 20% or less for several populations originating in Puget Sound. Low survival rates likely reduce overall smolt-to-adult return rates and limit recovery of Puget Sound steelhead populations. Harbor seals are generalist predators known to eat juvenile salmon in the Salish Sea. Harbor seals were captured in 2014 (12 seals) and 2016 (16 seals) and outfitted with acoustic telemetry receivers and GPS tags to quantify likely predation events and estimate foraging area overlap with acoustically tagged steelhead smolts. In 2014, mark-recapture estimates indicated that survival of steelhead through Central Puget Sound (Tacoma Narrows to Admiralty Inlet) was low (19%) and stationary tags were detected at harbor seal haulouts. In 2016 survival of steelhead through Central Puget Sound was high (69%), and no steelhead tags were detected stationary at harbor seal haulouts in the same region. However, in 2016, evidence of predation by harbor seals increased in the Nisqually estuary. Further, in both years, detection patterns of some tags were consistent with harbor seal movements, suggesting that tagged smolts had been eaten and were being carried by harbor seals. Steelhead smolt migratory behavior patterns through the Puget Sound epi-pelagic environment were very similar in the two years and do not likely explain the differences in survival or predation risk. We are currently exploring whether the increased presence of transient killer whales in Puget Sound and increases in anchovy abundance (an alternative prey source) may play a role in altering predation pressures and marine survival of steelhead smolts.