Evaluating the Conservation Potential of Tributaries for Native Fishes in the Upper Colorado River Basin

Abstract

We explored the conservation potential of tributaries in the upper Colorado River basin by modeling native fish species richness as a function of river discharge, temperature, barrier‐free length, and distance to nearest free‐flowing main‐stem section. We investigated a historic period prior to large‐scale water development and a contemporary period. In the historic period, species richness was log‐linearly correlated to variables capturing flow magnitude, particularly mean annual discharge. In the contemporary period, the log‐linear relationship between discharge and species richness was still evident but weaker. Tributaries with lower average temperature and separated from free‐flowing main‐stem sections often had fewer native species compared to tributaries with similar discharge but with warmer temperature and directly connected to free‐flowing main stems. Thus, tributaries containing only a small proportion of main‐stem discharge, especially those at lower elevations with warmer temperatures and connected to free‐flowing main stems, can support a relatively high species richness. Tributaries can help maintain viable populations by providing ecological processes disrupted on large regulated rivers, such as natural flow and temperature regimes, and may present unique conservation opportunities. Efforts to improve fish passage, secure environmental flows, and restore habitat in these tributaries could greatly contribute to conservation of native fish richness throughout the watershed.

Establishment of a Reproducing Population of Endangered Humpback Chub through Translocations to a Colorado River Tributary in Grand Canyon, Arizona

“…Laub et al. () suggested that the natural flow and thermal regimes in smaller Colorado River tributaries could support the ecological processes—which have been severely altered and are more difficult to restore in main‐stem rivers—that are necessary for the maintenance of large‐river species. While we must recognize recent exceptions, such as the resurgence of native fishes in much of the Colorado River in Grand Canyon (Kegerries et al., in press), climate change is expected to further constrain streamflow (Udall and Overpeck ), which could accelerate the replacement of native fishes by nonnative species (Ruhí et al.…”

“…). Havasu Creek has considerably smaller discharge than the suggested thresholds for tributaries with conservation potential for large river fishes (~25 m 3 /s; Laub et al ()), but flows and water temperatures are relatively unimpaired, exhibit characteristics that are consistent with those of spring‐fed perennial arid‐land rivers, and are reliable and consistent during base flows (Melis et al. ).…”

An Intermittent Stream Supports Extensive Spawning of Large‐River Native Fishes

“…; Laub et al. ). While these studies focused primarily on perennial tributaries, in some instances with enhanced flows resulting from irrigation projects, our study focused on a stream that is dry for a majority of the year.…”

A Tribute to Tributaries: Endangered Fish Distributions within Critical Habitat of the San Juan River, USA

“…; Laub et al. ; Hooley‐Underwood et al. ), most studies do not explore how small tributaries may affect main‐stem distributions of fishes.…”

“…For example, small tributaries in the Colorado River basin retain larvae (Haynes et al 1984), offer productive subadult growth (Webber et al 2012), connect habitats for spawning migrations (Weiss et al 1998), and provide refugia or foraging outside of mainstem environments (Cathcart et al 2018a). While tributary systems are recognized as crucial habitats for native desert fishes (Fraser et al 2017;Laub et al 2018;Hooley-Underwood et al 2019), most studies do not explore how small tributaries may affect main-stem distributions of fishes. This perspective is important because tributary systems and their junctions with main-stem rivers impart strong ecological forces that spatially structure fish populations (Fernandes et al 2004;Lopes et al 2019), communities (Osborne and Wiley 1992), and geomorphological processes throughout river networks (Benda et al 2004;Kiffney et al 2006).…”