Examining Alternative Water Management Strategies to Support Rio Grande Silvery Minnow Conservation Within and Across Years

Rio Grande Silvery Minnow (RGSM) are currently constrained to only 5% of their historic range, and their persistence is threatened by highly altered and impaired habitat conditions (Bestgen and Platania 1991). These habitat conditions have resulted from reduced spring and summer flows due to natural variability and anthropogenic water development and extraction, which have resulted in substantial geomorphic changes (Swanson et al. 2011). Successful conservation of this endangered species will require determination of how available flows can be managed to provide conditions supporting growth, reproduction, and survival of RGSM within and across a variety of water years. Previous research has identified that years with large spring high flow events and years with higher summer base flows support greater densities of RGSM during fall surveys (Dudley and Platania 2007; Archdeacon 2016; Walsworth and Budy 2021). However, given that years with large spring high flows also tend to have greater summer base flows, it remains unclear whether spring or summer flows (or both) are more critical to successful conservation of RGSM

Trophic Structure of Apex Fish Communities in Closed Versus Leaky Lakes of Arctic Alaska

Despite low species diversity and primary production, trophic structure (e.g., top predator species, predator size) is surprisingly variable among Arctic lakes. We investigated trophic structure in lakes of arctic Alaska containing arctic char Salvelinus alpinus using stomach contents and stable isotope ratios in two geographically-close but hydrologically-distinct lake clusters to investigate how these fish may interact and compete for limited food resources. Aside from different lake connectivity patterns (‘leaky’ versus ‘closed’), differing fish communities (up to five versus only two species) between lake clusters allowed us to test trophic hypotheses including: (1) arctic char are more piscivorous, and thereby grow larger and obtain higher trophic positions, in the presence of other fish species; and, (2) between arctic char size classes, resource polymorphism is more prominent, and thereby trophic niches are narrower and overlap less, in the absence of other predators. Regardless of lake cluster, we observed little direct evidence of arctic char consuming other fishes, but char were larger (mean TL = 468 vs 264 mm) and trophic position was higher (mean TP = 4.0 vs 3.8 for large char) in lakes with other fishes. Further, char demonstrated less intraspecific overlap when other predators were present whereas niche overlap was up to 100% in closed, char only lakes. As hydrologic characteristics (e.g., lake connectivity, water temperatures) will change across the Arctic owing to climate change, our results provide insight regarding potential concomitant changes to fish interactions and increase our understanding of lake trophic structure to guide management and conservation goals

A Lota lota consumption: trophic dynamics of non-native Burbot in a valuable sport fishery

Unintentional and illegal introductions of species disrupt food webs and threaten the success of managed sport fisheries. Although many populations of Burbot Lota lota are declining in the species’ native range, a nonnative population recently expanded into Flaming Gorge Reservoir (FGR), Wyoming–Utah, and threatens to disrupt predator–prey interactions within this popular sport fishery. To determine potential impacts on sport fishes, especially trophy Lake Trout Salvelinus namaycush, we assessed the relative abundance of Burbot and quantified the potential trophic or food web impacts of this population by using diet, stable isotope, and bioenergetic analyses. We did not detect a significant potential for food resource competition between Burbot and Lake Trout (Schoener’s overlap index = 0.13), but overall consumption by Burbot likely affects other sport fishes, as indicated by our analyses of trophic niche space. Diet analyses suggested that crayfish were important diet items across time (89.3% of prey by weight in autumn; 49.4% in winter) and across Burbot size-classes (small: 77.5% of prey by weight; medium: 76.6%; large: 39.7%). However, overall consumption by Burbot increases as water temperatures cool, and fish consumption by Burbot in FGR was observed to increase during winter. Specifically, large Burbot consumed more salmonids, and we estimated (bioenergetically) that up to 70% of growth occurred in late autumn and winter. Further, our population-wide consumption estimates indicated that Burbot could consume up to double the biomass of Rainbow Trout Oncorhynchus mykiss stocked annually (\u3e1.3 × 105 kg; \u3e1 million individuals) into FGR. Overall, we provide some of the first information regarding Burbot trophic interactions outside of the species’ native range; these findings can help to inform the management of sport fisheries if Burbot range expansion occurs elsewhere

Effective Conservation of Desert Riverscapes Requires Protection and Rehabilitation of In-Stream Flows With Rehabilitation Approaches Tailored to Water Availability

Desert riverscape rehabilitation practitioners must contend with compounding effects of increasing human water demand, persistent drought, non-native species establishment, and climate change, which further stress desert riverine ecosystems such as rivers in the Colorado River basin, United States. Herein, we provide our perspective on the importance of natural flows, large floods in particular, for successful conservation and rehabilitation of riverscapes. We present ideas developed from our experience with rehabilitation projects across multiple desert tributary rivers with varying levels of habitat degradation and water abstraction. We propose spatially extensive measures such as protection of in-stream flows, tailoring rehabilitation efforts to available annual water availability, and working with nature using low-tech process-based techniques to more completely address the mechanisms of habitat degradation, such as flow reduction and vegetation-induced channel narrowing. Traditionally, rehabilitation efforts in the Colorado River basin take place at relatively small spatial extents, at convenient locations and, largely focus on reducing non-native plant and fish species. We suggest that we need to think more broadly and creatively, and that conservation or recovery of natural flow regimes is crucial to long-term success of almost all management efforts for both in-stream and riparian communities

Movement Patterns of Resident and Translocated Beavers at Multiple Spatiotemporal Scales in Desert Rivers

Wildlife translocations alter animal movement behavior, so identifying common movement patterns post-translocation will help set expectations about animal behavior in subsequent efforts. American and Eurasian beavers (Castor canadensis; Castor fiber) are frequently translocated for reintroductions, to mitigate human-wildlife conflict, and as an ecosystem restoration tool. However, little is known about movement behavior of translocated beavers post-release, especially in desert rivers with patchy and dynamic resources. We identified space-use patterns of beaver movement behavior after translocation. We translocated and monitored nuisance American beavers in desert river restoration sites on the Price and San Rafael Rivers, Utah, USA, and compared their space use to resident beavers after tracking both across 2 years. Resident adult (RA) beavers were detected at a mean maximum distance of 0.86 ± 0.21 river kilometers (km; ±1 SE), while resident subadult (RS) (11.00 ± 4.24 km), translocated adult (TA) (19.69 ± 3.76 km), and translocated subadult (TS) (21.09 ± 5.54 km) beavers were detected at substantially greater maximum distances. Based on coarse-scale movement models, translocated and RS beavers moved substantially farther from release sites and faster than RA beavers up to 6 months post-release. In contrast, fine-scale movement models using 5-min location intervals showed similar median distance traveled between RA and translocated beavers. Our findings suggest day-to-day activities, such as foraging and resting, were largely unaltered by translocation, but translocated beavers exhibited coarse-scale movement behavior most similar to dispersal by RSs. Coarse-scale movement rates decreased with time since release, suggesting that translocated beavers adjusted to the novel environment over time and eventually settled into a home range similar to RA beavers. Understanding translocated beaver movement behavior in response to a novel desert system can help future beaver-assisted restoration efforts to identify appropriate release sites and strategies

Establishing a Baseline to Assess Impact of Restoration Actions Reconnecting Bear Lake Tributaries to Increase Resilience and Abundance of Native Fishes

Stream fragmentation due to the construction of dams, diversions, and road crossing culverts have limited the ability of native migratory fishes to access the distinct habitats required to complete their life history, contributing to widespread declines in abundance and distribution. The Bear Lake Cutthroat Trout (Oncorhynchus virginalis spp., recently reclassified from O. clarkii), represent a unique adfluvial life history variant, living in the lake and migrating up tributary streams to spawn. However, development of water resources and construction of roads in the valley surrounding Bear Lake reduced their ability to access their historic spawning grounds, leading to the near extirpation of the species from the lake by the 1950s. Recent efforts to reestablish connectivity between the lake and its tributaries has resulted in substantial increases in recruitment of wild Cutthroat Trout to the population, such that wild individuals accounted for the majority of the population in a recent annual lake monitoring survey. As such, further increasing connectivity to tributary streams may increase the production and resilience of the wild Cutthroat Trout population in Bear Lake. North Eden Creek, on Bear Lake’s eastern shore, is home to a relict population of Bear Lake Cutthroat Trout that are isolated in the headwaters. Adfluvial Cutthroat Trout enter the stream during their spawning migration, but are blocked from ascending upstream of the intersection with North Cisco Road by an impassable culvert. Trout Unlimited and partners are planning to replace the culvert in Fall of 2025 to allow adfluvial spawners to access the additional spawning habitats upstream of the road crossing. To understand how this planned restoration action ultimately impacts the Cutthroat Trout population of North Eden Creek, we conducted a review of historical documents and data collection efforts, and designed and implemented a monitoring plan to assess the physical habitat, fish assemblage, and aquatic invertebrate community along an elevational gradient of North Eden Creek, including sites both below and above the culvert. Cutthroat Trout and non-native Brook Trout (Salvelinus fontinalis) were the only two species of fish captured upstream of the culvert at North Cisco Road, while two additional native fishes (Utah Chub Gila atraria and speckled dace Rhinichthys osculus) were also captured downstream of the culvert. An additional native species (Utah Sucker Catostomus ardens) has also been observed downstream of the culvert in recent years, but was not captured in our samples. Brook Trout were found at all sites inhabited by Cutthroat Trout, and represent potential competitors for resources and predators of juvenile Cutthroat Trout. Importantly, fish were restricted to headwater habitats and to habitats downstream of the culvert, being absent throughout the middle and low elevation reaches upstream of the culvert. Physical habitat conditions demonstrated clear elevational patterns along North Eden Creek. Riparian vegetation was most abundant in lower elevation sites both upstream and downstream of the culvert, and was very limited in middle and high elevation reaches. The low elevation sites maintaining riparian vegetation cover do not experience cattle grazing, while the upper and middle elevation reaches do. Undercut bank habitat was abundant in high elevation sites, but very limited in middle and low elevation sites. Gravel substrates were more abundant in high elevation sites, while cobble substrates were most available in low elevation sites, and middle elevation sites were dominated by silty substrates. Stream temperatures were highest in middle elevation reaches, where temperatures exceeded 7-day incipient lethal temperatures for at least part of the summer. Headwater and low elevation temperatures never exceeded this thermal limit, and were generally lower than in middle elevation sites, demonstrating complex, nonlinear thermal patterns along the length of the river. Aquatic invertebrates were most abundant at the low and high elevation sites, and much less abundant in middle elevation reaches. Additionally, the proportional contribution of sensitive taxa (Ephemeroptera, Trichoptera, Plecoptera) was greatest in high and low elevation reaches, and lower in middle elevation reaches. Taken together, the physical habitat and aquatic invertebrate data suggest middle elevation reaches are suboptimal and even unsuitable at specific times of the year, thus limiting the distribution of both native and non-native trout. As such, while we expect reestablishing connectivity for adfluvial Cutthroat Trout to increase the availability of spawning habitat and the production of juvenile Cutthroat Trout, the middle elevation reaches of the stream are unlikely to support large increases in abundance of trout without further habitat restoration efforts. We recommend repeating the monitoring surveys presented in this report, alongside additional efforts to monitor the abundance of spawning adfluvial trout entering the stream each year to assess the population level response of Cutthroat Trout to the planned culvert replacement. We provide a description of the monitoring protocol in an appendix. If surveys are repeated every 1-3 years, managers and stakeholders will be able to determine the effects of culvert replacement and any subsequent habitat restoration efforts on both the adfluvial and resident populations of Cutthroat Trout in North Eden Creek

Consequences of Didymo Blooms in the Transnational Kootenay River Basin

Stream habitat changes that affect primary consumers often indirectly impact secondary consumers such as fishes. Blooms of the benthic algae Didymosphenia geminata (Didymo) represent one such habitat change known to affect stream macroinvertebrates. However, the potential indirect trophic impacts on fish consumers via modifications to their diet are poorly understood. The overall goal of this project was to determine if Didymo blooms in streams of the Kootenay River basin of British Columbia and Montana affect the condition and growth of fishes, and to see whether trophic mechanisms were responsible for any observed changes. We therefore quantified the diet, condition, and growth rate of trout, charr, and sculpin in a paired, Didymo vs. reference study, during the summer of 2018 and across a gradient of Didymo abundance in 2019. In the 2018 study, trout diets were 81% similar despite obvious differences in the composition of macroinvertebrate assemblages between the Didymo and reference streams. Trout abundance was higher in the stream with Didymo, but the amount of invertebrates in the drift was higher in the stream without Didymo. Growth rate and energy demand by individual trout was similar between the two streams. In the 2019 study, across a gradient of coverage, Didymo abundance was correlated only with the percent of aquatic invertebrates in trout diets and did not affect diets of charr or sculpin. Variation in fish condition was low across study streams. Thus, Didymo blooms may impact trout diets to a small extent, but we found no evidence this impact translates to changes in condition or growth. The relationship of fish abundance to Didymo blooms bears further study, but we found no obvious trophic mechanisms that would explain any differences. We suggest future studies prioritize research on potential impacts during winter months and on species with limited mobility that may be most greatly impacted by Didymo

Angler Catch Rates, Opinions, and Abiotic Variable Relationships in the Lower Logan River, Utah

Summer base flows for rivers are critical for maintaining water quality, healthy fish populations, and a functional aquatic ecosystem. Low summer base flows can increase water temperatures and lower dissolved oxygen levels. These conditions can cause Brown Trout (Salmo trutta) energetic stress and result in lower angler catch. The goal of this study was to determine if low river flows and higher water temperatures influence angler catch rates of Brown Trout on the lower Logan River, Utah and to better understand angler use of the lower river. We performed a creel survey on approximately 6.4 km of the lower Logan River from 1 April to 31 October 2019 to calculate mean monthly angler catch rates. We used continuous collection of stream temperature and flow from a river gage within the survey reach to calculate monthly means. Total Brown Trout caught were 1,481 and total angling effort was 2,147 hours for an overall catch rate of 0.7 fish per hour (fph) for the survey period. The highest angler catch rate (1.2 fph) was in June with the highest mean monthly discharge (16 m3/s) and a mean monthly water temperature of 9.6 °C. The lowest angler catch rate (0.41 fph) occurred in September with a mean monthly discharge of 2.12 m3/s and a mean monthly water temperature of 11.2°C. We found a positive correlation between flow rates and angler catch rates (R2 = 0.37), and a negative correlation between water temperatures and angler catch rates (R2 = 0.42), although neither were statistically significant. Our data suggest that even on a higher-than-average runoff year, angler success is impacted by low summer base flows. Maintaining increased river flow during typical summer low-flow time periods could increase angler catch rates and, ultimately, provide even greater satisfaction with this fishery. We also determined educational signage and outreach could be extremely influential, as anglers knew little about regulations of the fish community in general

Keeping It Classy: Classification of Live Fish and Ghost PIT Tags Detected With a Mobile PIT Tag Interrogation System Using an Innovative Analytical Approach

The ability of passive integrated transponder (PIT) tag data to improve demographic parameter estimates has led to the rapid advancement of PIT tag systems. However, ghost tags create uncertainty about detected tag status (i.e., live fish or ghost tag) when using mobile interrogation systems. We developed a method to differentiate between live fish and ghost tags using a random forest classification model with a novel data input structure based on known fate PIT tag detections in the San Juan River (New Mexico, Colorado, and Utah, USA). We used our model to classify detected tags with an overall error rate of 6.8% (1.6% ghost tags error rate and 21.8% live fish error rate). The important variables for classification were related to distance moved and response to monsoonal flood flows; however, habitat variables did not appear to influence model accuracy. Our results and approach allow the use of mobile detection data with confidence and allow for greater accuracy in movement, distribution, and habitat use studies, potentially helping identify influential management actions that would improve our ability to conserve and recover endangered fish