ABSTRACT: Exploratory correlation analysis of multi-site summer temperature and flow data in the Fraser River Basin.

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Abstract

Fisheries researchers currently use lower Fraser River summer temperature and flow conditions as indices of the total environmental exposure experienced by migrating adult sockeye salmon (Oncorhynchus nerka). If lower Fraser temperature (measured 165km up-stream of the river mouth at Qualark) and flow (measured 150 km upstream at Hope) values are not well correlated to values elsewhere in the Fraser Basin (ranging from 330km to 970km upstream), the current indices may not reflect the true exposures experienced by the migrants. The purpose of this report was to compile available multisite temperature and flow information for the Fraser River and to determine whether data from lower river stations are appropriate environmental indices for the basin as a whole. In general, lower Fraser environmental conditions were well correlated (r > 0.6) to conditions upriver; however, correlation strength decreased as a function of increasing distance and/or slower migration rates (i.e. increased lag time between measurements) and the magnitude of encountered temperatures and flows was highly variable. Earlier in the summer, river temperatures and flows appear to be more strongly influenced by large spatial scale processes such as regional air temperatures and spring snowmelt runoff. Synoptic weather changes, flow management regimes, and influences; from lake-headed systems may all contribute to localized differences in river environment, particularly towards late summer. Our results show that adult salmon encounter a range of temperature and flow conditions along their freshwater migration route and that these values may not be consistently well-correlated to lower river conditions, particularly for populations with natal spawning grounds > 500km from the ocean or for populations entering the river after mid-August. These results provide rationale for further exploration into the use of multi-site, alternate-site or cumulative exposure models to better reflect the impact of freshwater migration conditions on the health and spawning success of Fraser River sockeye salmon populations.

Bibliography of Canadian Geomorphology