Contrasting Functional Performance of Juvenile Salmon Habitat in Recovering Wetlands of the Salmon River Estuary, Oregon, U.S.A.

Abstract

For an estuarine restoration project to be successful it must reverse anthropogenic effects and restore lost ecosystem functions. Restoration projects that aim to rehabilitate endangered species populations make project success even more important, because if misjudged damage to already weakened populations may result. Determining project success depends on our ability to assess the functional state or "performance" and the trajectory of ecosystem development. Mature system structure is often the desired "end point" of restoration and is assumed to provide maximum benefit for target species; however, few studies have measured linkages between structure and function and possible benefits available from early recovery stages. The Salmon River estuary, Oregon, U.S.A., offers a unique opportunity to simultaneously evaluate several estua-rine restoration projects and the response of the marsh community while making comparisons with a concurring undiked portion of the estuary. Dikes installed in three locations in the estuary during the early 1960s were removed in 1978, 1987, and 1996, creating a "spacefor-time substitution" chronosequence. Analysis of the marsh community responses enables us to use the development state of the three recovering marshes to determine a trajectory of estuarine recovery over 23 years and to make comparisons with a reference marsh. We assessed the rate and pattern of juvenile salmon habitat development in terms of fish density, available prey resources, and diet composition of wild juvenile Oncorhynchus tshawytscha (chinook salmon). Results from the outmigration of 1998 and 1999 show differences in fish densities, prey resources, and diet composition among the four sites. Peaks in chinook salmon densities were greatest in the reference site in 1998 and in the youngest (1996) site in 1999. The 1996 marsh had higher densities of chironomids (insects; average 864/m 2 ) and lower densities of amphipods (crustaceans; average 8/m 3 ) when compared with the other sites. Fauna differences were reflected in the diets of juvenile chinook with those occupying the 1978 and 1996 marshes based on insects (especially chironomids), whereas those from the 1987 and reference marshes were based on crustaceans (especially amphipods). Tracking the development of recovering emergent marsh ecosystems in the Salmon River estuary reveals significant fish and invertebrate response in the first 2 to 3 years after marsh restoration. This pulse of productivity in newly restored systems is part of the trajectory of development and indicates some level of early functionality and the efficacy of restoring estuarine marshes for juvenile salmon habitat. However, to truly know the benefits consumers experience in recovering systems requires further analysis that we will present in forthcoming publications.

Community composition and diet of fishes as a function of tidal channel geomorphology

“…Miller & Simenstad 1997, Mathieson et al 2000, Gray et al 2002, Barletta et al 2003, Bottom et al 2005. The fyke nets were composed of a 3.2 mm (1/8 inch) mesh mouth, body, and live trap in the cod end, as well as adjustable 6.4 mm (1/4 inch) mesh wings that attached to the net mouth and extended to the sides of each channel and to the marsh edge.…”

“…The uppermost reaches of channel systems provide nursery grounds for early life stages of fishes, whereas downstream sections provide low-tide refuge for larger nekton using adjacent subtidal regions (Weinstein 1979, Rozas & Zimmerman 2000. First-order channels are highly productive, providing low predation pressure, reduced competition, diminished flow velocities, lower temperatures, and an extensive food supply for large numbers of juvenile fishes (Shenker & Dean 1979, Bozeman & Dean 1980, Rozas & Hackney 1984, Rozas & Odum 1987b, Gray et al 2002. Rozas et al (1988) found that small first-order channels (coined 'rivulets') contained a significantly higher biomass of fishes than larger adjacent channels and appeared to be the preferred pathway for marsh surface access.…”

Early Ecological Responses to Hydrologic Restoration of a Tidal Pond and Salt Marsh Complex in Narragansett Bay, Rhode Island

“…These tidal restrictions result in altered hydrology and biogeochemistry, and degraded vegetation, nekton, and bird communities compared to unrestricted salt marshes (BURDICK et al, 1997;EERTMAN et al, 2002;GRAY et al, 2002;LLANSO, BELL, and VOSE, 1998;MYSHRALL et al, 2000;PORTNOY, 1991PORTNOY, , 1999PORTNOY and GIBLIN, 1997;RAPOSA, 2002;ROMAN, GARVINE, and PORT-NOY, 1995;ROMAN, NIERING, and WARREN, 1984;ROMAN et al, 2002;SINICROPE et al, 1990;VOSE and BELL, 1994;WARREN et al, 2002). Salt marshes are integral to the proper functioning of estuarine systems, and in recognition of the negative effects of tidal restrictions, efforts are now underway to restore tidal flow and ecological function to many of these degraded systems.…”

Invertebrate Community Composition Across Inundation Regimes and Its Potential to Reduce Plant Stress

“…Salmon River estuary, located north of Lincoln City, Oregon, just south of Cascade Head Preserve, is approximately 800 hectares, half being emergent marshlands (Gray et al 2002). Since 1978, the US Forest Service (USFS) has completed a series of projects to remove dikes and tidal gates within the estuary, returning almost 70% of the historic wetlands to tidal inundation (Gray et al 2002).…”

“…Since 1978, the US Forest Service (USFS) has completed a series of projects to remove dikes and tidal gates within the estuary, returning almost 70% of the historic wetlands to tidal inundation (Gray et al 2002). Focal plots for this study were located on an island of low marsh, north of the main channel, at approximately river kilometer 1.6, in an area that had never been diked (Figure 3-1).…”