Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8838
Title: Population, habitat, and marine location effects on early marine survival and migration behavior of Puget Sound steelhead smolts
Author: M. E. Moore, B. A. Berejikian
Publication Year: 2017
Journal: Ecosphere
Keywords: nearshore migration,steelhead,survival,habitat,reciprocal transplant

Steelhead trout (Onchorhynchus mykiss) smolts suffer high mortality rates during their rapid migration through the Salish Sea. Among-population variability in mortality rates may reflect i) genetic fitness variation among populations, ii) freshwater environmental effects on fish condition, or iii) differences in local marine conditions upon seawater entry. A reciprocal transplant experiment was conducted to separate the influence of freshwater effects (combined effects of population and freshwater environment) from effects of local marine conditions on survival of two Puget Sound steelhead populations. Steelhead smolts from the Green River in Central Puget Sound (urbanized and hatchery-influenced) and the Nisqually River in South Puget Sound (less urbanized; no hatchery influence) were tagged with acoustic telemetry transmitters and released back into their natal river or transported and released into the other river. Population-of-origin had little influence on probability of surviving the migration through Puget Sound. However, smolts released into the Green River had higher survival through Puget Sound (17%) than smolts released into the Nisqually River (6%); the extra 60-km migration segment for the Nisqually-released fish accounted for most of the difference between the two release locations. Neither fork length nor translocation influenced survival, though release date did affect survival of Nisqually population smolts regardless of their release location. Residence time and behavior in the two estuaries were similar, and no effects of population-of-origin or release date were evident. Marine travel rates also did not differ between populations, release dates, or release locations. This study indicates that mortality occurring in the Salish Sea is likely driven by processes in inland marine environments, moreso than latent effects of freshwater environments on fish condition.


This manuscript describes a reciprocal transplant experiment conducted to separate the confounded effects of population and freshwater habitat from those of marine entry location on steelhead smolt survival through Puget Sound. We used Cormac-Jolly-Seber survival models to determine the variables that had the biggest effect on probability of survival from release in freshwater through four or five (dependent on release location) migration segments. We also compared migration behavior in the context of two very different (i.e., urbanized and non-urbanized) estuarine habitats, finding very similar behavior as well as evidence of predation.

Theme: Recovery and rebuilding of marine and coastal species
Foci: Describe the relationships between human activities and species recovery, rebuilding and sustainability.
Characterize the population biology of species, and develop and improve methods for predicting the status of populations.