Chinook salmon are well known for utilizing natal river tidal deltas, non-natal “pocket estuaries” (nearshore lagoons and marshes), and other estuarine habitats for rearing during outmigration (Reimers 1973, Healey 1980, Beamer et al 2003). Several studies have linked population responses to availability of estuary habitat, either by examining return rates of groups of fish given access to different habitat zones (Levings et al. 1989) or by comparing survival rates of fish from populations with varying levels of estuary habitat degradation (Magnusson and Hilborn 2003). These studies support the hypothesis that estuarine habitat is vital for juvenile Chinook salmon. However, these necessarily coarse-scale studies have ignored how large-scale estuarine habitat restoration within a watershed contributes to population characteristics. These issues may be critical to understand how to best restore Chinook salmon populations, as many estuaries within Puget Sound and elsewhere have been converted to agriculture and urbanization land uses. For example, the Duwamish River has lost more than 99% of its tidal delta habitat (Simenstad et al 1982), while the Skagit River, which contains the largest tidal delta in Puget Sound, has lost 80-90% of its aquatic habitat area (Collins et al. 2003).
Our goal is to understand changes in population characteristics (primarily abundance, productivity, and life history diversity) of wild Chinook salmon in response to reconnection and restoration of estuarine habitat. Effectively evaluating the population response to estuary restoration hinges on our ability to address several questions. First, we need to examine the influence of estuary restoration on population change at a relevant spatial scale (see below) while simultaneously taking into account the influence of larger-scale environmental patterns. In addition, we need to identify what habitats best support juvenile Chinook salmon, how these habitats influence growth and survival, and what biological and physical factors limit productivity and capacity in the estuary.
The current monitoring effort
These goals require long-term monitoring tied to restoration efforts. We are currently monitoring Skagit River Chinook salmon via a long-term interagency programs involving sampling of outmigrants at Mt Vernon (Washington Department of Fish and Wildlife, WDFW), fyke trapping of fish rearing in the tidal delta (Skagit River System Cooperative, SRSC), beach seining of nearshore habitats in Skagit Bay (SRSC), and townetting of offshore areas in Skagit Bay (Northwest Fisheries Science Center, NWFSC). This program provides us a system-wide analysis of patterns of abundance and life history diversity across the migration season.
Greene, C.M. and Beamer, E.M., 2006. Monitoring of population responses by Skagit River Chinook salmon to estuary restoration. Northwest Fisheries Science Center, Seattle, WA. pp. 17.
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