A comparison of the behavior and survival of juvenile coho salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss) in a small estuary system

We used radio and acoustic telemetry to study the behavior and survival of wild steelhead trout (Oncorhynchus mykiss) and hatchery coho salmon (Oncorhynchus kisutch) and steelhead outmigrants in a small coastal estuary during two years. Survival was generally low for hatchery fish but more variable, both within and between years, for wild steelhead. The rate of downstream movement in the river varied both within and between species and was generally not correlated with flow. Both hatchery and wild steelhead tended to spend less than a day in the estuary, and tended to move downstream on outgoing tides. In contrast, hatchery coho salmon spent a longer period of time in the estuary (~ 8 d). On several occasions, coho salmon were observed moving both upstream and downstream between the upper (freshwater) and lower (saline) zones of the estuary. We also documented a high incidence of predation by avian and mammalian predators on coho outmigrants.

► Measured juvenile salmon survival and behavior in an estuary.
► Wild and Hatchery steelhead spent little time in estuary.
► Variable, high, and unexplained mortality in steelhead.
► Significant cormorant depredation of hatchery coho.
► Implications for life cycle survival models.