Foraging and Growth Potential of Juvenile Chinook Salmon after Tidal Restoration of a Large River Delta

Abstract

We evaluated whether restoring tidal flow to previously diked estuarine wetlands also restores foraging and growth opportunities for juvenile Chinook Salmon Oncorhynchus tshawytscha. Several studies have assessed the value of restored tidal wetlands for juvenile Pacific salmon Oncorhynchus spp., but few have used integrative measures of salmon performance, such as habitat-specific growth potential, to evaluate restoration. Our study took place in the Nisqually River delta, Washington, where recent dike removals restored tidal flow to 364 ha of marsh—the largest tidal marsh restoration project in the northwestern contiguous United States. We sampled fish assemblages, water temperatures, and juvenile Chinook Salmon diet composition and consumption rates in two restored and two reference tidal channels during a 3-year period after restoration; these data were used as inputs to a bioenergetics model to compare Chinook Salmon foraging performance and growth potential between the restored and reference channels. We found that foraging performance and growth potential of juvenile Chinook Salmon were similar between restored and reference tidal channels. However, Chinook Salmon densities were significantly lower in the restored channels than in the reference channels, and growth potential was more variable in the restored channels due to their more variable and warmer (2°C) water temperatures. These results indicate that some—but not all—ecosystem attributes that are important for juvenile Pacific salmon can recover rapidly after large-scale tidal marsh restoration.

Received April 23, 2014; accepted July 9, 2014

ACKNOWLEDGMENTS

Funding for this study was provided by the U.S. Environmental Protection Agency, U.S. Fish and Wildlife Service, U.S. Geological Survey, Nisqually Indian Tribe, and Ducks Unlimited. A. T. David was supported by a National Science Foundation Graduate Research Fellowship. Numerous people were instrumental in completing fieldwork for the project, including W. Duval, E. Perez, S. Stepetin, K. Kautz, T. Friedrich, E. Villegas, M. Holt, L. Belleveau, P. Markos, B. Ryken, J. Barham, C. Iverson, H. Tucker, H. Minnella, and C. Guthrie. C. Levy, B. Armbrust, E. Morgan, and J. Cordell helped with the identification of stomach contents; A. Calahan created Figure 1; and T. P. Quinn and D. A. Beauchamp reviewed drafts of the manuscript and provided guidance for the study. We thank the Nisqually NWR and the Nisqually Indian Tribe for access to study sites. We also thank the anonymous reviewers for their suggestions for improving the manuscript. The use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.