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Scale of monitoring influences interpretation of stream habitat restoration results for juvenile Chinook salmon

Carlos M. Polivka, Rhiannon A. Volking, Shannon M. Claeson, Rachel D. Hosman, and Pacific Northwest Research Station (Portland, Or.)
Stream restoration, Monitoring, Chinook salmon, Habitat, and Fish habitat improvement
Stream habitat restoration in the Entiat River, Washington, has increased juvenile Chinook abundance in pools with engineered logjams (ELJs); however, high spatial, temporal, and inter-species variation complicates distinguishing treatment effects between restored and unrestored habitat. Here we show that the scale of post restoration effectiveness monitoring can also be a confounding factor in such studies. In three stream reaches, we conducted snorkel surveys of (1) spatially randomized untreated habitat in which we also randomized survey area, and (2) restored (ELJ) habitat that included varying amounts of the surrounding stream area. Although we regularly observed more young-of-the-year Chinook salmon in restored than in unrestored habitat, this effect was very localized. After controlling for reach effects, fish density in untreated habitat was not affected by proximity to ELJs. Increasing the survey area increased total fish abundance, however, fish density decreased regardless of habitat type, indicating that ELJ structures did not necessarily increase fish abundance at the whole-reach scale. Specifically, increasing the survey area around a pool created by an ELJ by two to three times the restored pool area resulted in density measurements indistinguishable from unrestored habitat surveys. We conclude that whole-reach scale effectiveness monitoring surveys may give misleading results that dilute the effect of ELJs; therefore, monitoring should match the scale of specific restoration treatments.
1 online resource (16, 1 pages ) : illustrations, color map.
U.S. Department of Agriculture. Pacific Northwest Research Station
Research note
USDA publications
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