Current riparian management objectives in the Pacific Northwest promote both retention of existing conifers and conversion of hardwood-dominated areas to conifers. Although understanding of relationships between riparian vegetation and salmonid prey availability is growing, temporal variation in these relationships is poorly understood. Seasonal fluxes in availability of aquatic and terrestrial invertebrate prey for coastal cutthroat trout (Oncorhynchus clarki clarki) were investigated by estimating invertebrate biomass from aquatic (benthos and drift) and allochthonous (terrestrial) sources in three watersheds in the Oregon Coast Range. To investigate the influence of vegetation type on food sources, samples were collected in each watershed from stream sections dominated by deciduous, conifer, and mixed vegetation. During each sample period, diet was assessed by examining gut contents of captured trout. Stream discharge appeared to be an influential factor regulating seasonal fluxes of aquatic invertebrate biomass in the benthos and drift. Total allochthonous invertebrate biomass at deciduous and mixed vegetation sites (64 and 61 mg·m⁻²·day⁻¹, respectively) was almost 30% higher than at coniferous sites (45 mg·m⁻²·day⁻¹). Although aquatic insects dominated the total gut contents during this study, prey from terrestrial origin was more common during summer and fall. These results suggest that systematic removal of deciduous vegetation in riparian zones to promote conifers may have unintended consequences on the food resources of coastal cutthroat trout and the productivity of aquatic food webs in the Pacific Northwest. / Graduation date: 2004

Thesis (Ph. D.)--University of Washington, 1975. / Bibliography: leaves [90]-98.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 52-60). Also available on the World Wide Web.

Thesis (M.E.S.)--The Evergreen State College, 2008. / Title from title screen (viewed 2/25/2009). Includes bibliographical references (leaves 32-33).

Coastal cutthroat trout (Oncorhynchus clarkii clarkii) are the apex predator in the Capilano Reservoir. This thesis investigates cutthroat predation via bioenergetic modelling and demography, and genetic analysis of hybridization with coastal rainbow / steelhead trout (O. mykiss irideus). The bioenergetics model, based on stomach content analyses, reservoir temperature and growth rates, in conjunction with predator abundance, estimates that adult trout in the reservoir consumed 6.4% of coho (O. kisutch) smolt production in 2010. No evidence of cutthroat predation on juvenile steelhead out-migrants was detected, and a gape prey maximum of 36% of predator body length was found. Moderate hybridization rates between cutthroat and rainbow trout were detected, as well as previously unknown pure strains of adult rainbow trout in reservoir waters, indicating reservoir residualization. Cutthroat trout are currently a 'second tier' management species in the Capilano Watershed, and greater understanding and appreciation of their adfluvial-lacustrine life history will facilitate informed decision-making for trout conservation and restoration, and coho management in the reservoir and the Capilano Watershed.

This research focused on features of a genetically isolated population of cutthroat trout (Oncorhynchus clarki) in the Triangle Lake basin of coastal Oregon. A falls at the outlet of Triangle Lake has blocked upstream migration of trout and anadromous salmonids into the basin. Cutthroat trout were found throughout the six study streams of the Triangle Lake basin in association with other native fishes and introduced warmwater fishes. Warmwater species (e.g. Centrarchidae) were restricted largely to the lakes of Triangle Lake basin, and did not comprise a significant part of the stream fish fauna. Salmonids and cottids dominated the upper forested reaches of the basin, whereas nonsalmonids dominated the lower reaches. The middle reaches contained a transitional fish community between the upper and lower reaches. Reach type was a major factor influencing cutthroat trout density and size distribution. Areal densities of cutthroat trout were highest in the upper reaches and lowest in the lower reaches with the exception of 0+ cutthroat trout, which occurred at similar densities in all reaches. The highest frequency of 1+ cutthroat trout occurred in the middle reaches, whereas the highest frequency of 0+ cutthroat occurred in the lower reaches. Within reaches, channel unit type influenced the density and age structure of cutthroat trout. Pools and rapids had the highest densities of cutthroat trout, whereas riffles, glides, and cascades had lower densities. Larger trout were found primarily in pools and rapids. Planted steelhead fry (Oncorhynchus mykiss) were found in two streams, Congdon Creek and Lake Creek. Although most steelhead fry leave the basin as smolts, some steelhead appear to become resident and may hybridize with native cutthroat trout. Cutthroat trout spawning was observed from late December 1987 through late May 1988. Differences in the time and place of spawning may serve to genetically isolate two populations of cutthroat trout in Triangle Lake basin. One population may be lake dwelling as adults and spawn lower in the basin in late spring. The other population may be stream dwelling and spawn in the winter during higher flows, which allows them to spawn in the upper reaches of the basin. / Graduation date: 1994

Thesis (PhD)--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Billie L. Kerans. Includes bibliographical references.

Thesis (M.S.)--University of Nevada, Reno, 2007. / "August 2007." Includes bibliographical references (leaves 29-34). Online version available on the World Wide Web.

Thesis (M.S.)--University of Nevada, Reno, 2008. / "May, 2008." Includes bibliographical references (leaves 25-30). Online version available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 113-123). Also available on the World Wide Web.