Historical records for Pacific salmon reflect substantial variability. Great controversy exists over the causes, as climatic change and many anthropogenic factors, (e.g. commercial fishing, habitat alterations, hatcheries and dams) may have impacted salmon stocks. The main objectives of this thesis were to develop paleolimnological approaches to reconstruct past sockeye salmon population dynamics and apply these tools to infer trends in Alaska over the past ~2,200 years.
Because large numbers of sockeye salmon may return to nursery lakes to spawn and die, salmon-derived nutrients can be significant in terms of the total nutrient budget. Fossil diatom assemblages and d15N isotopes, preserved in nursery lake sediments, were found to be robust indicators of past salmon-derived nutrients, and such analyses can be used to reconstruct past sockeye salmon population dynamics. Application of diatom-based phosphorus transfer functions to the fossil diatom assemblages from two sockeye salmon nursery lakes demonstrated the impact that sockeye salmon carcasses can have on lake trophic state. Using these paleolimnological indicators, striking decadal- and century-scale variability in several Alaskan sockeye salmon populations were inferred prior to any intensive anthropogenic activity (e.g. commercial fishing). Regionally coherent trends in sockeye salmon populations from Kodiak Island were evident over the past ~2,200 years. A comparison of these sockeye salmon trends to reconstructions of other fish abundances from the North Pacific revealed a synchronous, but 180o out of phase pattern. These data, together with paleoclimatic and paleoceanographic reconstructions, suggest that climatic forcing is responsible for the long-term ecosystem changes recorded in the North Pacific.
The relative importance of the freshwater versus the marine environment in sockeye salmon production was also assessed, by comparing past trends between two nursery lake types: clear water and stained lakes. The synchronicity of past sockeye salmon dynamics between lake types suggested that conditions in the North Pacific Ocean have an overriding influence.
Overall, this thesis has demonstrated that paleolimnology can provide powerful insights into sockeye salmon population dynamics and the factors that affect adult production trends. This knowledge could, in turn, help to predict future sockeye salmon abundances and develop sustainable management plans for this species.

Email: Irene.GregoryEaves@science.uottawa.ca