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UBC Theses and Dissertations

Trophic phasing of juvenile chum salmon (Oncorhynchus keta Walbaum) and harpacticoid copepods in the Fraser River Estuary, British Columbia D'Amours, Denis


Within the environmental approach for the study of fluctuations in fish population abundance, factors that may regulate the overlap in time and space (phasing) of fishes, food supply, and predators, are sought. This trophic phasing analysis is based on the recognition that production of food is a process at least partially independent of the production of consumers. Trophic phasing analysis was applied in investigating production of chum salmon in the Fraser River estuary. Juvenile chum salmon were captured near a tidal flat; the abundance of salmon near the flat was highest in late May in 1985 and in early June in 1986. These salmon relied heavily on harpacticoid copepods as a food source. Individual taxa as well as the assemblage of main prey harpacticoids also had periods of highest abundance in the water column. The blooming period of the prey harpacticoid assemblage coincided with the appearance in the sediment of warming episodes. These warming episodes result from interactions between the daily heat cycle and specific tide patterns. Variations in the degree of overlap of the periods of highest abundance of salmon and harpacticoids could affect the survival of the fishes. The degree of overlap of those periods was hindcasted using indices for the temporal patterns of abundance of salmon and harpacticoids on the flat. The median date of downstream migration at a counting station upstream was used for the salmon; the timing of the second annual occurrence of tide conditions giving rise to a warming event in the sediment was used for harpacticoids. Difference in time between the two events was taken as a phasing index accounting for two degrees of freedom in the process of fish production. There is suggestion of a non-monotonic relationship between the index of survival of even broodyear chum salmon and the hindcasted phasing index.

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