Integrating Nonnative Species in Niche Models to Prioritize Native Fish Restoration Activity Locations along a Desert River Corridor

Abstract

The efficient allocation of restoration resources is critical for the effective conservation of species. Here, we developed an ecological niche model to predict the response of three imperiled desert fishes to potential restoration actions along the longitudinal gradient of a desert river. The San Rafael River, Utah, is home to a complex of three endemic fishes (Flannelmouth Sucker Catostomus latipinnis, Bluehead Sucker C. discobolus, and Roundtail Chub Gila robusta; referred to as the "three species"). Like many Colorado River basin tributaries, the river is overallocated for human use, has experienced extensive physical degradation, and is now home to several nonnative fish species. To determine the factors most limiting to the three species, we first fit random forest models to fish CPUE and habitat data. We next combined these models with a longitudinal habitat survey and modeled nonnative species abundance to predict the continuous distribution of the three species in the lower San Rafael River, under current conditions and following simulated restoration. Nonnative fishes were important negative predictors of Flannelmouth Sucker and Bluehead Sucker relative abundance, and broadscale habitat variables were important positive predictors for all of the three species. Each of the three species was predicted to experience a significant increase in abundance following simulated eradication of nonnative fishes. Responses to simulated reach-specific habitat restoration were dependent on the reach restored, demonstrating that the choice of restoration location is critical. Nonnative species removal and restoring degraded reaches near already suitable habitat were predicted to be the most beneficial to the three species. Ecological niche models developed at the river scale, and incorporating both physical and biotic predictor variables, can provide spatially explicit information that appropriately parallels the spatial distribution of the needs of endemic fishes and can facilitate effective management and conservation decisions.

Remarkable response of native fishes to invasive trout suppression varies with trout density, temperature, and annual hydrology

“…Moreover, adult flannelmouth sucker were annually observed spawning prior to our study during spring, but juveniles had not been rearing in Bright Angel Creek (Otis 1994;Weiss et al 1998) until 2015. Our findings are consistent with those of Walsworth and Budy (2015), suggesting complete eradication of invasive fishes is not necessary to secure benefits to imperiled flannelmouth and bluehead suckers. They predicted suppression of invasive fishes of >70% as a prerequisite to positive responses in a native long-lived cyprinid (roundtail chub, Gila robusta) and a more pronounced decline of ≥90% before native sucker populations would benefit.…”

Increasing drought favors nonnative fishes in a dryland river: evidence from a multispecies demographic model

“…As a result of nonnative species introduction and their establishment and proliferation from reservoirs, the number of nonnative species equals or exceeds native species in most watersheds throughout the southwestern United States (Pool et al. , Walsworth and Budy ).…”

“…Widespread dam construction, flow diversions, and surface and groundwater abstraction for growing human populations have significantly altered environmental regimes in the region, creating conditions that threaten native species persistence and promote nonnative fishes (Minckley and Deacon 1968, Olden and Poff 2005, Strecker et al 2011. As a result of nonnative species introduction and their establishment and proliferation from reservoirs, the number of nonnative species equals or exceeds native species in most watersheds throughout the southwestern United States (Pool et al 2010, Walsworth andBudy 2015).…”

High‐resolution riparian vegetation mapping to prioritize conservation and restoration in an impaired desert river

“…Bluehead sucker adults preferentially use riffle habitat with coarse substrate, roundtail chub adults use deeper pools with cover, flannelmouth sucker adults use diverse habitats, and juvenile life stages of each species use shallow, slow‐velocity, backwater habitats (Bezzerides & Bestgen ). In the San Rafael River, the distribution of these native fish is correlated with the availability of complex habitat, comprised of riffles, pools, and backwaters (Budy et al ; Walsworth & Budy ).…”

“…Due to its impaired condition and conservation importance, in 2013, the U.S. Department of Interior Bureau of Land Management (BLM) developed a large‐scale restoration plan to improve riparian and fish habitat on the San Rafael River (Laub et al ). The plan acknowledges that a key component in managing the river system is to identify areas with desirable aquatic and riparian habitat as conservation zones and impaired areas with the highest likelihood of improvement as restoration zones (Wissmar & Beschta ; Walsworth & Budy ). Cottonwood are a desirable native tree species that can improve instream habitat for native fishes through large wood contributions to the channel (Minckley & Rinne ).…”