Juvenile salmon and steelhead occupancy of stream pools treated and not treated with restoration structures, Entiat River, Washington

Abstract

We observed habitat occupancy by juvenile Chinook salmon (Oncorhynchus tschawytscha) and steelhead trout (Oncorhynchus mykiss) at in-stream habitat restoration structures constructed in the Entiat River, Washington, USA. In 2009–2013, fish abundance measurements during rearing (July–October) showed high temporal variability in pools with restoration structures. Both species were more abundant at restored pools than at natural pools in early summer (July), but this difference was typically absent by September. Fish response to restoration structures also varied across years. When looking only at restored pools, there were strong seasonal fluxes in parameters describing the effects of temperature, water depth, and current velocity on fish abundance. Significant interaction terms such as current velocity × depth and temperature × current velocity were present for both species, suggesting that these may be important physical attributes improved by restoration. Through extensive sampling in untreated habitat, both within the treated segment and in nearby control segments, we found that when higher Chinook abundance was observed at restored pools, it was apparently attributable to an increase in habitat capacity and not due to depletion of fish from natural habitat in the same segment. Steelhead habitat selection was too inconsistent for conclusions about capacity, but we did not observe evidence that structures depleted untreated habitat.