Quantifying the habitat preferences of the stoneflyPteronarcys californicain Colorado

Abstract

The salmonfly (Pteronarcys californica) is a large stonefly species that is ecologically important and recreationally significant to anglers in coldwater river systems throughout the western United States. Salmonflies are sensitive to disturbance and pollution and are considered an indicator of quality coldwater stream habitat. They are declining in range and abundance in some river systems and their extirpation from several western rivers has led to restoration attempts including habitat improvement projects and direct reintroductions. These efforts could be improved with a clear understanding of the causes of these declines, a quantitative description of the species' preferred habitat, and practical management recommendations for the restoration of habitat where it has been lost. The objective of this study was to measure variables that describe the physical habitat of sites supporting varying densities of salmonflies in Colorado. Width to depth ratio, bed slope, D50 sediment size, percent fine sediment, and embeddedness were measured at 18 riffle sites and compared to an index of salmonfly density estimated over 3 years. Correlation analysis and multiple linear regression with model selection were used to identify important variables. Salmonfly density was highest at sites with low amounts of fine sediment, low cobble embeddedness, and large cobble size. Fine sediment (particles < 2 mm) was the single best predictor of salmonfly density and ranged from 0-6% at sites with high salmonfly densities. As habitat characteristics influence the range and density of salmonflies in Colorado and elsewhere, results from this study can inform land use practices, flow management, and river restoration activities to benefit this important indicator species.

Emergence phenology of the giant salmonfly and responses by birds in Idaho river networks

“…Salmonfly populations are declining or have been lost from many rivers of the western U.S. for reasons not well understood (Nehring et al, 2011;Birrell et al, 2019;Kowalski and Richer, 2020). This conservation concern provides added context for our findings for ecological, sociocultural, and economic reasons.…”

“…Even shifts at the scale of days in salmonfly emergence timing could mean that this prey resource would be unavailable to these birds upon their arrival in the region, especially if salmonfly emergence timing also became more synchronized in response to habitat homogenization. Climate change and river habitat homogenization, driven by processes like flow regulation, channelization, or changes in riparian vegetation, are changing river thermalscapes, and this could threaten salmonfly persistence (Nehring et al, 2011;Birrell et al, 2019;10.3389/fevo.2023.804143 Frontiers in Ecology and 13 frontiersin.org Kowalski and Richer, 2020), change important to population processes and predator satiation, or alter the mechanisms underlying spatial variation in their phenology. For example, a more homogenous thermal regime might amplify the synchrony of salmonfly emergence, which could favor salmonflies if it increased satiation of predators.…”

Dietary composition and fatty acid content of giant salmonflies (Pteronarcys californica) in two Rocky Mountain rivers

“…In addition, reliance on high-quality autochthonous primary producers such as diatoms that are also sensitive to anthropogenic river alteration may further limit availability of preferred food resources (Larras et al, 2017). Salmonflies are declining throughout the western United States and this trend is likely to continue as the climate warms (Anderson et al, 2019;Kowalski & Richer, 2020;Walters et al, 2018). Maintaining habitat that meets the need of salmonflies will be key to conserving and restoring salmonfly populations in reaches where they are at risk of extirpation.…”

“…Additionally, recreational fishing during salmonfly emergence is an economic boost for local communities. However, salmonflies are declining in abundance in many western rivers and their range is contracting due to rising water temperatures and sedimentation (Anderson et al, 2019;Birrell et al, 2019;Kowalski & Richer, 2020). Salmonflies are already extirpated from certain river systems in Montana, Utah, and Colorado (Birrell et al, 2019;Elder & Gaufin, 1973;Stagliano, 2010).…”

Expanding catchment-scale hydrologic restoration in suburban watersheds via stream mitigation crediting—A Northern Kentucky (USA) case study

“…RBP habitat quality has long been used as a surrogate for biological community integrity (Plafkin et al 1989;Barbour et al 1999), and individual components of RBP such as low amounts of ne sediment, low embeddedness, and coarse/stable substrate continue to be highly correlated to the abundance and density of sensitive taxa such as Ephemeroptera, Plecoptera, and Trichoptera compared to purely geometric indices such as stream slope and the width to depth ratio (e.g. Kowalski and Richer 2020).…”