Gravel Augmentation Increases Spawning Utilization by Anadromous Salmonids: A Case Study From California, Usa

Abstract

Anadromous salmonid diversity and abundance worldwide have been adversely impacted by anthropogenic forces, and millions of dollars are spent each year on stream habitat restoration and enhancement. However, there is a paucity of data comparing site use by salmonids before and after enhancement implementation, and few studies examine the specific environmental conditions that determine whether salmonids utilize an enhanced site. This study examines the use of gravel augmentation to improve spawning site utilization by Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) on the Lower American River, California, USA. Spawning increased across all augmentation sites for both species, although there were species‐specific and year‐specific differences in the degree to which a site was utilized and in the spatial distribution of redds in relation to substrate size, habitat features and other redds. There were also differences in redd architecture across sites that were related to differences in gravel size. This study illustrates that gravel augmentation projects can enhance spawning habitat for salmonids where spawning beds have degraded but that species‐specific and site‐specific attributes and gravel size can influence the relative effectiveness of a project. Copyright © 2013 John Wiley & Sons, Ltd.

Legacy effects on sediments in river corridors

“…Thus far, these types of experiments have utilized primarily gravel-sized sediment, primarily in an effort to enhance fish spawning sites (Zeug et al, 2014), although sand has been added to the Platte River in Nebraska, USA to restore nesting habitat for migratory birds (Smith, 2011). Gravel augmentation has had limited success, partly because of the complicated outcomes that arise from characteristics such as volume and grain-size distribution of sediment supplied, frequency and timing of augmentation, method of sediment delivery, and interactions between the introduced sediment, flow regime, and channel geometry (Bunte, 2004;Sklar et al, 2009).…”

Juvenile Salmonid Utilization of Floodplain Rearing Habitat After Gravel Augmentation in a Regulated River

“…Increased spawning and/or successful incubation following augmentation may also have led to increased juvenile salmonid abundance at the site, a potentially confounding effect for increased juvenile abundance observations following augmentation. Restoration site spawning activity did increase following augmentation (Zeug et al ., ). Therefore, observed augmentation effects on juvenile abundance should be interpreted with caution.…”

“…Seasonal flow patterns were relatively similar across all years, except during the post‐augmentation 2010–2011 winter season (Figure ). During this season, incubation period flows were extremely high, which would be expected to reduce juvenile abundance by potentially scouring salmon redds, increasing sediment deposition entombing embryos, prematurely transporting newly emerged fry out of the system, and population dilution because of greater water volume (Schuett‐Hames et al ., ; Zeug et al ., ). Even so, we observed a highly significant positive augmentation effect despite the extreme (and potentially adverse) flow conditions during this post‐augmentation year.…”

“…). For example, gravel augmentation has been used extensively worldwide to improve salmonid spawning and incubation conditions (Merz et al ., ; Barlaup et al ., ; Pulg et al ., ; Zeug et al ., ), while structural element placement (e.g. woody material and boulders) can improve rearing habitat conditions (Roni et al ., ).…”

A salmonid individual‐based model as a proposed decision support tool for management of a large regulated river

“…These restoration efforts may have different effects depending on their composition, size, and location. For example, substantial resources are put toward adding gravel to increase salmon spawning habitat in sedimentstarved rivers below dams; however, there is often little effort to quantify the benefits of these costly actions, particularly the interactions with other key factors such as flow and temperature (Zeug et al 2013). These complex interactions between ecological drivers and the limited management options highlight the need for decision support tools (DSTs, a system which is designed to solve ill-structured problems, has easy to use and powerful interface, can combine models with data, can explore alternatives in the solution space, can supporting different decision-making methods, and allows for interactive and recursive problemsolving; Sullivan 2002) for regulated river management.…”