Using landscape ecology principles to prioritize habitat restoration projects across the Columbia River Estuary

To increase survival of diverse Columbia River salmon populations and life history types, we developed a landscape framework for habitat restoration to assess and reduce habitat fragmentation, and thereby improve habitat functions. For the last two decades, aquatic habitat has been restored in the Columbia River Estuary (U.S.A.) to aid salmon and steelhead (Oncorhynchus spp.) listed under the Endangered Species Act. The 234-km long estuary exhibits tidal to fluvial gradients in hydrology, sedimentology, and ecology, punctuated by large tributary rivers, cities, and land uses; it has lost two-thirds of its historical floodplains and wetlands to development. Since 2009, an expert panel has assessed potential benefits of proposed restoration projects based on habitat "opportunity" (accessibility to juvenile salmon) and "capacity" (attributes supporting salmon production). These criteria favored large restoration projects located near the mainstem river, but they were insufficient for assessing a project's benefits due to geographic location relative to existing habitat. Our landscape framework applies the concept of restoring and conserving habitat "stepping stones" of appropriate size and location to benefit juvenile salmon growth and survival throughout their estuary residency and migration. We also compared contemporary and historical landscape conditions to identify restoration priorities. We improved our restoration project assessments by evaluating each project's benefits to juvenile salmon according to its location in the estuary relative to other habitat. Our approach operationalizes landscape ecology-based decisions within the Columbia River Estuary for migratory salmon and is applicable to other large estuary systems with migratory aquatic species.