Identifying habitat protection and restoration needs requires understanding habitat condition across large geographic areas such as a watershed.

Project Title

Lost watersheds: barriers, aquatic habitat connectivity, and species persistence in the Willamette and Lower Columbia basins

Description Draft Manuscript Abstract

Large portions of watersheds and streams are lost to anadromous fishes because of anthropogenic barriers to migration. The loss of these streams and rivers has shifted the distribution of available habitat, often reducing the diversity of available habitats and the quantity of high quality habitat. The impact of barriers and lost habitat on Pacific salmon populations varies with the location, density, and distribution of in-stream barriers. We combined existing inventories of barriers to adult fish passage in the Willamette and Lower Columbia basins and identified 1491 anthropogenic barriers to fish passage, blocking 14,931 km of streams. We quantified and compared stream quality, land cover, and physical characteristics of lost versus currently accessible habitat by watershed, assessed the effect of barriers on the variability of available habitats, and investigated potential impacts of habitat reduction on endangered or threatened salmon populations. The majority of the study watersheds have lost greater than 40% of total fish stream habitat. Overall, 40% of the physically suitable steelhead spawning habitat, 60% of riparian habitat in good condition, and 30% of all coniferous land cover was upstream of barriers in areas no longer accessible to anadromous fish. Hydrologic and topographic watershed characteristics were associated with trends in barrier location, density and habitat effects across watersheds. Population-based abundance scores for spring Chinook salmon were strongly correlated with the magnitude of habitat lost and the number of lowland fish passage barriers. Characteristics of barrier and habitat distribution presented in this paper illustrate that barrier removal projects and mitigation for in-stream barriers should be done with consideration for both magnitude and quality of habitat lost, and barrier density per fish population.

Investigators

Ashley Steel and Mindi Sheer (Conservation Biology Division)

Support

NOAA Fisheries

Project Status

Data analyses ongoing

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