Long-term response of sockeye salmon (Oncorhynchus nerka) nursery lakes to climate and watershed management activities in British Columbia (Canada)
Sockeye salmon (Oncorhyncus nerka) are a heavily exploited species. Owing to their large geographical distribution and use of both freshwater and oceanic habitats, sockeye salmon are exposed to various stressors at the local, regional and Pacific-wide scale. As such, assessing the relative influence of these stressors on sockeye salmon populations can be challenging. The goal of this thesis was to further develop our understanding of the influence of local anthropogenic and climate factors on the freshwater nursery lakes upon which sockeye salmon depend. This was accomplished by investigating the impact of watershed disturbances in three large and highly valued sockeye salmon nursery lakes: Seton, Anderson and Babine lakes (British Columbia, Canada). The results indicate that anthropogenic disturbances in the watershed of these nursery lakes changed the pelagic producer communities, which may indirectly and/or directly reduce the capacity of the lake to sustain populations of sockeye salmon. The results also highlighted the importance of the local ecosystems responses to climate change which can modify the nursery ecosystem and indirectly influence the freshwater survival of juveniles O. nerka. This thesis also investigates the long-term variations in inferred sockeye salmon population dynamics. The reconstruction of the salmon population of Seton Lake over the last ~600 years indicate that the sockeye salmon population of Seton Lake was much larger prior to the onset of commercial harvesting. The low frequency (~300 year), high-amplitude (~3‰ oscillation in δ15N) fluctuations displayed by the Seton Lake records appeared in anti-phase with some Alaskan populations, which may indicate that coastal oceanic processes at the mouth of the Fraser River regulates the Seton Lake sockeye salmon population through a regional mechanism, other than the Alaskan Gyre and California current. Together, the findings of these studies suggest that predicting O. nerka production in the future may become increasingly challenging because of the simultaneous and potentially additive effects of local and Pacific-wide changes in climate and anthropogenic stressors.
URI for this recordhttp://hdl.handle.net/1974/27501
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