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How does coarse gravel augmentation affect early-stage Chinook salmon Oncorhynchus tshawytscha embryonic survivorship?



Early-stage Chinook salmon Oncorhynchus tshawytscha embryos were incubated in artificial redds that mimicked hyporheic conditions in gravel-augmented habitat to assess survivorship. Two complementary experiments were conducted where units varied along gradients of (1) increasing interstitial flow velocity (0·05–2·50 cm s−1) in a uniformly coarse (particles ≥22 mm) sediment mixture and (2) increasing sediment porosity with interstitial flow velocity held constant. Embryonic survivorship increased moderately along a gradient of interstitial flow velocity, while survivorship among units with varying sediment porosities was consistent. No evidence for flow-induced agitation and mortality was observed. Results suggest that high interstitial flow velocities may confer a moderate advantage for incubating salmonid embryos when conditions that typically reduce embryonic mortality (i.e. low concentrations of fine particles) are ideal.