Journal of Environmental Management (Elsevier) | November 9th, 2022
Summary
The decline of Pacific salmon (Oncorhynchus spp.) populations over the last few decades has stimulated major restoration efforts across the Pacific Northwest to improve t
The decline of Pacific salmon (Oncorhynchus spp.) populations over the last few decades has stimulated major restoration efforts across the Pacific Northwest to improve the status of these iconic fishes. The leading factors contributing to the decline of Pacific salmon include watershed degradation and water diversions, which result in part from widespread dam construction across the United States (Moyle, 1994). Early river restoration actions primarily focused on physical habitat alterations (e.g., in-stream habitat improvement, fish passage; Barinaga, 1996; Bernhardt et al., 2005), while more recent work has centered around restoring natural processes (Johnson et al., 2019). Since socioeconomic and political complications are typically too great for dam removal projects to be feasible, reconciliation ecology, which encourages the accommodation of both human and wildlife needs in a human-dominated landscape, can be a more effective approach to restoration (Rosenzweig, 2003; Moyle et al., 2017). Rather than the elusive goal of returning rivers to a natural flow regime, the aim can be to attain functional environmental flows to support beneficial flow-ecology relationships (Poff et al., 2017). Dams can be operated to reduce some of their detrimental effects by releasing flows that improve downstream habitat through the preservation of key hydrologic signals upon which biophysical processes and native biological communities depend (Yarnell et al., 2020). Four functional flow components were identified for Mediterranean montane streams: wet-season initiation flows, peak magnitude flows, spring recession flows, and dry-season low flows; see Yarnell et al. (2015) for a description about the importance of each key functional component. Several studies have identified the need to further assess linkages between streamflow, invertebrate prey availability, and drift-foraging dynamics for consideration in future restoration plans for juvenile salmonids (Weber et al., 2014; Naman et al., 2016; Lusardi et al., 2018). The focus of this study is to assess the impact of dam-release flows imitating one of those functional flow components, peak magnitude flows, on invertebrate drift as a food resource for juvenile salmonids.