Graduation date: 2008Anadromous coastal cutthroat trout Oncorhynchus clarkii clarkii may be highly dependent on estuaries, passing through them multiple times during their lifetime. However, few studies have investigated estuarine use by coastal cutthroat trout and it is often thought that estuaries serve primarily as migration corridors rather than rearing areas. We used both PIT tag and acoustic tracking techniques in 2002 and 2003 to investigate habitat use, movement, and life history variation within the population of coastal cutthroat trout in the Salmon River estuary, Oregon. Evidence of site fidelity was observed in both the PIT-tagged and acoustically tagged fish, with 70% of PIT tagged fish being recaptured at their previous capture site and most acoustically tagged fish residing in one location for at least 25 days. Ninety percent of fish relocated 1.7 km upstream or downstream showed directional movement toward the original site of capture, and half of those eventually took up residence there. Cutthroat trout used main channel sites more frequently than marsh channel sites, and deeper sites more frequently than shallower sites. Contrary to published results for most other coastal populations, Salmon River cutthroat trout rear in the estuary for much of the year. We identified two main life history types: an “ocean migrant” form that migrates rapidly through the estuary and out to sea, and an “estuarine resident” form that resides in the estuary for the spring and summer. In addition, we found evidence of other life history types: coastal cutthroat trout that rear mainly in the estuary but make brief forays into the near shore ocean, and some that rear in the estuary throughout winter. We saw no difference in mean length at tagging between ocean migrants and estuarine residents, suggesting that the stimulation for migrating to the ocean was not size related. Half of the acoustically tagged fish exhibited the estuarine life history type. We compared growth rates of ocean migrants and estuarine residents by classifying PIT-tagged fish into life history types based on their recapture history. We found no evidence of a growth advantage for ocean migrants, although sample size was small. This study suggests that the estuarine life history is an important migratory behavior within the continuum of life histories for coastal cutthroat trout in the Salmon River. Our results imply that conservation of coastal cutthroat trout may depend on recovery and maintenance of suitable estuarine rearing habitat.