Early Marine Survival of Steelhead Smolts in Puget Sound

Megan Moore1, Barry Berejikian1, Fred Goetz2, Thomas Quinn2, Sayre Hodgson3, Ed Connor4, and Andrew Berger5

1NOAA Fisheries, Northwest Fisheries Science Center, 2University of Washington, School of Fisheries and Aquatic Sciences, 3Nisqually Indian Tribe, 4Seattle City Light, 5Puyallup Indian Tribe

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Smolt-to adult survival rates for Puget Sound steelhead populations have declined substantially over the last 25 years and remain at or near historic lows. From 2006-2009, nearly 1,400 steelhead smolts from 9 watersheds within Puget Sound were tracked from river mouth to the Pacific Ocean using acoustic telemetry to: (1) estimate early marine survival through Puget Sound, (2) identify common areas of abnormally high mortality along the migration route, and (3) to identify factors that may influence survival. Cormac-Jolly-Seber mark-recapture models were used to jointly estimate survival and detection rate at telemetry arrays. Estimated survival rates from river mouths to near the Pacific Ocean ranged from 2.7% (White River hatchery smolts in 2009) to 44.8% (Skokomish River wild smolts in 2006), and averaged 16.8% for all populations. Factors influencing survival included population, migration year, and rearing type (i.e., hatchery or wild), while geographic region, body length, and tag type (i.e., 7mm or 9mm) showed lesser effects. Comparison of survival rates between migration segments implicated central Puget Sound and Admiralty Inlet as potential areas of heightened mortality. Early marine survival rates estimated here are very low considering that steelhead smolts spend only about two to three weeks in Puget Sound before entering the Pacific Ocean. Mortality in Puget Sound may be a major driver behind low observed smolt-to adult survival rates. This study addresses a major gap in steelhead marine life history knowledge and can help to inform future Puget Sound steelhead recovery planning efforts.