Techniques for Evaluating a Fry Release Strategy for Tule Fall Chinook Salmon at Spring Creek National Fish Hatchery

Since its inception in 1901 and through the 1970’s Spring Creek National Fish Hatchery (NFH) performed tule fall Chinook salmon (Oncorhynchus tshawytscha) fry releases which usually occurred during February in the Columbia River. The practice was curtailed in 1974 due to inadequate adult returns and reinstituted in the 1990’s when the hatchery again experienced surplus returns. Past evaluations suggested that the fry releases from Spring Creek NFH survived at a rate of 0.0022% during a study in the late 1950’s and early 1960’s (unpublished U.S. Fish and Wildlife Service data). The addition of a warm water well in the early 1990’s provided the ability to manipulate incubation water temperature and use otolith-based marking methods to assess survival of this early release. With fry releases marked, managers would be able to measure their contribution to adult returns to the hatchery. Introduction