Critical Uncertainties, Environmental Variability, and Biotic Response to Habitat Restoration: Can We Detect Change?

Despite a substantial knowledge base for juvenile salmon (Oncorhynchus spp.) ecology in estuarine habitats, the role of tidal freshwater habitats is not as well understood. Elucidating the relationships between biotic and abiotic attributes in potentially highly variable environments is driven by the need for understanding the effects of large scale ecosystem restoration efforts in the lower Columbia River and estuary (LCRE). Our research focused on addressing critical uncertainties of juvenile Chinook salmon (O. tshawytscha) life history attributes (size, density, and genetic stocks) in shallow tidal freshwater habitats. By sampling two distinct areas within the tidal freshwater portion of the LCRE, we determined how early life history characteristics of salmon are expressed along varying spatio-temporal gradients. Next, we considered how the patterns of life history attributes related to other elements of the aquatic ecosystem measured during our study; including prey production, terrestrial vegetative characteristics, habitat type, and water quality attributes. Our findings indicate that, despite environmental interannual variability, many biotic metrics are consistently responsive along spatio-temporal gradients. These findings support an ecosystem-based strategy for restoration as well as provide data for future monitoring and design frameworks to determine the effectiveness of restoration actions.