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 S...
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| Format: | Text |
| Language: | English |
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Western CEDAR
2018
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| Online Access: | https://cedar.wwu.edu/ssec/2018ssec/allsessions/465 https://cedar.wwu.edu/cgi/viewcontent.cgi?article=2900&context=ssec |
| Summary: | 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. |
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