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

Abstract

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.

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