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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.

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.

Razorback Sucker Xyrauchen texanus is a large-bodied, long-lived species endemic to the Colorado River Basin. This species historically ranged throughout the basin from the Colorado River delta in Mexico to Wyoming and Colorado. Currently, the species persists ,in a small portion of its historical range with the help of intensive management efforts including augmentation. Recruitment to adult life stages is extremely limited in the wild, but is documented consistently in Lake Mead. Research and monitoring efforts in Lake Mead are ongoing since 1996 and have recently expanded to include the Colorado River inflow area and portions of lower Grand Canyon. Despite evidence of recruitment, the current population size in Lake Mead and Grand Canyon is believed to be small (data) and susceptible to stochastic effects. This raised interest in the potential to augment the population to prevent loss of genetic diversity and increase abundance and distribution in general, as well as explore recruitment bottlenecks. To address critical uncertainties surrounding this management option and to brainstorm other potential options, a Planning Committee and Steering Committee made up of representatives of state (Arizona, Nevada), tribal (Hualapai Tribe, Navajo Nation), and federal (Bureau of Reclamation, National Park Service, and U.S. Fish and Wildlife Service) management agencies convened an Expert Science Panel (ESP; 2021), to consider augmentation and management strategies for Razorback Sucker in Lake Mead and Grand Canyon. The purpose of this report is to summarize those findings.

MotivationThe BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.Main types of variables includedThe database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.Spatial location and grainBioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2).Time period and grainBioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year.Major taxa and level of measurementBioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.Software format.csv and .SQL.

This first issue of the journal of Ecology of Freshwater Fish (EFF) was published in September 1992, a creation of Dr's Erik Mortensen and Javier Lobón-Cerviá. During the 25 years that has passed since then, Javier has been the editor in chief, handling a large number of submissions. He oversaw the operations of EFF, and helped grow the journal, increasing it in both importance and impact. Over this time, the scientific community has also observed a dramatic and rapid change in publication strategies, with the focus moving from paper to digital publication. The number of submissions has also increased, and since 2006 onwards on average 200 submissions have been handled per year.

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 (>1.3 × 105 kg; >1 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.

Hough-Snee, N. et al., (eight authors). 2014. Riparian vegetation and instream wood dynamics in streams of the interior Columbia River basin. Society of American Foresters Intermountain Meeting, Logan, UT.

Riparian areas of the Colorado Plateau Ecoregion (CPE) are among the most productive and diverse ecosystems in this semiarid region. These small, yet vital ecosystems support a myriad of aquatic and terrestrial species while simultaneously providing valuable ecosystem services. Maintenance of these important ecosystems requires accurate delineation and characterization. Nevertheless, accurate and comprehensive riparian zone mapping currently doesn’t exist. This project aims to accurately delineate valley bottoms, while characterizing riparian areas and rivers throughout the CPE. The results of this project will provide a comprehensive CPE wide inventory of the distribution and condition of riverine riparian areas. This riparian inventory will serve as an important baseline tool for threat abatement, and for monitoring ecological responses to natural and anthropogenic actions and change.

Hough-Snee, N., B.B. Roper, J.M. Wheaton, P. Budy and R.L. Lokteff. 2013. Riparian vegetation communities change rapidly following passive restoration at a northern Utah stream. Ecological Engineering 58: 371-377. DOI: 10.1016/j.ecoleng.2013.07.042

Hough-Snee, N., B.B. Roper, J.M. Wheaton, P. Budy and R.L. Lokteff. 2013. Riparian vegetation communities change rapidly following passive restoration at a northern Utah stream. Ecological Engineering 58: 371-377. DOI: 10.1016/j.ecoleng.2013.07.042

We completed a large-scale field experiment in four tributaries of the Logan River, Utah, where the largest metapopulation of imperiled Bonneville cutthroat trout Oncorhynchus clarkii utah persists. We documented the spatial and temporal distributions of spawners, quantified substrate use versus substrate availability, and evaluated differences in hatch and emergence fry success between and among sites in relation to habitat characteristics. We observed considerable variability in the timing, magnitude, and duration of spawning among study areas (streams), in part as a function of a variable, multipeaked hydrograph. Nevertheless, across study areas, >70% of redds were constructed on the final descending limb of the hydrograph. Despite large differences in the amount of spawning substrate available, Bonneville cutthroat trout utilized a narrow range of substrate and sizes (3–80 mm) similar to that utilized by other subspecies of cutthroat trout, albeit biased towards larger sizes. Water temperatures generally remained below the recommended range (6–17◦C) for spawning; however, the viability of this metapopulation of cutthroat trout suggests that the recommended temperature range for spawning is overestimated for this subspecies and (or) does not account for local thermal adaptation. Hatch varied from 43% to 77% and emergence survival from 39% to 65% among streams, and within-stream variability was substantial; both survival rates declined significantly as a function of increased fine sediment concentrations. Egg development rates were nearly 50% greater in a high- elevation tributary where redd counts were also lowest. In high, mountain systems with short growing seasons, this incubation delay likely presents a significant growth disadvantage for age-0 trout. Our research enhances our understanding of Bonneville cutthroat trout spawning ecology and early survival and provides critical information for aiding in the development of benchmarks for their recovery. Effective conservation efforts should be directed towards minimizing anthropogenic activities that result in excess sedimentation in their critical spawning tributaries.

Nutrients can load directly to either the epilimnion or metalimnion of lakes via either differential inflow depths of tributaries or intentional fertilization of discrete strata. We evaluated the differential effects of epilimnetic versus metalimnetic nutrient loading using 17-m-deep mesocosms that extended into the deep chlorophyll layer of oligotrophic Pettit Lake in the Sawtooth Mountains of Idaho. Addition of nitrogen plus phosphorus stimulated primary production nearly identically (2.4- to 4-fold on different dates) in both treatments, with the production peaks occurring in the strata where nutrients were added. The metalimnetic fertilization, however, resulted in equal or greater stimulation of chlorophyll a and phytoplankton biovolume than when nutrients were added directly to the epilimnion. Periphyton growth was stimulated 10–100 times more by epilimnetic fertilization than by metalimnetic fertilization and diverted nutrients from the planktonic autotrophs. These results suggest that the development of deep chlorophyll layers may be influenced by plunging river inflows that carry nutrients to the metalimnion and that metalimnetic lake fertilization may be useful as a tool for increasing lake productivity while reducing the impact on water quality.

We used dual-beam hydroacoustics and echo integration techniques, combined with midwater trawling and gillnetting, to assess the abundance and distribution of the endangered Snake River juvenile sockeye salmon and resident kokanee (both Oncorhynchus nerka) in Sawtooth Valley lakes of Idaho during September 1991 and 1992. Abundance of O. nerka varied among the four lakes containing this species (12,500–257,000) and varied between years in Redfish Lake (86,400 in 1994 and 241,000 in 1992) and Alturas Lake (230,000 in 1991 and 257,000 in 1992). In Alturas Lake, where piscivore densities were high and zooplankton densities were low, small acoustic targets (≤18 cm long) were nearly absent from the limnetic zone during daylight, and high densities remained in colder intermediate depths (15–30 m) during crepuscular and nocturnal periods. In Redfish Lake, where predator density was much lower and zooplankton density was higher, targets concentrated in schools at 25–30 m during daylight, dispersed into the upper 10 m at dusk, then were broadly distributed over the upper 30 m at night. In Pettit and Stanley lakes, nocturnal distributions of smaller (3–7 cm) and intermediate (7–18 cm) target sizes were skewed toward the epilimnion, and larger targets remained in the metalimnion or upper hypolimnion. The different diel vertical distribution patterns suggested that juvenile O. nerka exposed to limited food and high predation risk consumed smaller rations and maximized bioenergetic efficiency. Populations with higher food supplies and exposed to lower piscivore densities exploited the higher epilimnetic prey densities and temperatures at night and crepuscular periods to maximize growth but deviated further from bioenergetic efficiency. Populations responded differently to the unique combination of constraints that limit potential sockeye salmon smolt production at each lake. Consequently, different management strategies may be needed in each lake.

"Phytoplankton production in lake ecosystems is frequently controlled by amounts of nitrogen and phosphorus (Smith 1982, Elser et al. 1990), as well as minor- and micro-nutrients (Wurtsbaugh & Horne 1983, Wurtsbaugh 1988, Lovstad & Bjorndalen 1990). Nutrient limitation is often studied to determine which nutrient(s) should be reduced to control lake eutrophication (Schindler 1974(. Conversely, nutrients have been used for decades to stimulate plankton and, subsequently, fish production in aquaculture (Bardach et al. 1972). More recently, lake fertilization has been used to augment salmon runs for commercial exploitation (Hyatt & Stockner 1985, lye et al. 1988), and it has been suggested for reversing losses in lake productivity due to decreases in anadromous salmon populations (Koenings & Burkett 1987). After returning to their natal lakes, adult salmon spawn, die, and decompose, often releasing significant amounts of marine-derived nutrients into the freshwater ecosystems (Juday et al. 1932, Kline et al. 1990). Koenings & Burkett (1987), for example, calculated that sockeye salmon carcasses contributed nearly 60% of the annual phosphorus loading to an Alaskan lake. Because phosphorus loading is often important in determining phytoplankton abundance in lakes (Vollenweider 1976), declines in returning salmon can lead to decreases in lake productivity, and lower production of the juvenile salmon that rear in the lake for 1-2 years. In the Sawtooth Valley of Idaho, USA, runs of the endangered Snake River sockeye salmon (Oncorhynchus nerka) to five rearing lakes in Idaho have declined more than 99% over the last century, primarily because of dams constructed along their migration route (Rieman et al. 1991, Bevan et al. 1994). Thousands of salmon once returned to these lakes (Bjornn et al. 1968). The decline of the Snake River sockeye has undoubtedly reduced nutrient loading and may have contributed to the current low fish production in the lakes. Although the primary threat to these salmon is mortality during downstream migration, it may be possible to help save this race of salmon by fertilizing the rearing lakes to elevate them a higher level of productivity. This remedy should increase the growth rates and abundances of wild and hatchery-produced sockeye salmon that will bin introduced into the lakes. Here we report on laboratory and field nutrient-addition bioassays to determine if lake fertilization could be used to stimulate phytoplankton production and aid in the recovery Snake River sockeye salmon."

We investigated how epilimnetic fertilization would affect chlorophyll levels and light penetration of oligotrophic sockeye salmon (Oncorhynchus nerka) lakes and how the resulting self-shading would affect primary production of the prominent deep chlorophyll maxima (DCM) of the lakes. Epilimnetic nutrient additions to large mesocosms (330 m3) in Redfish Lake, Idaho, increased levels of primary productivity and chlorophyll a but decreased Secchi depths and light available in the metalimnion and hypolimnion. Redfish Lake and other Sawtooth Valley (Idaho) lakes had DCM in which the mean chlorophyll a peaks were 240-1000% of mean epilimnetic chlorophyll a concentrations. The DCM existed at low light levels and accounted for 36-72% of the lakes' primary production. Simulations using photosynthesis-irradiance (P-I) curves demonstrated that fertilization would increase predicted water column primary production by 75-101%. Most of this increase occurred in the epilimnion, with only a slight decrease occurring in the DCM as the result of increased shading.

We examined the potential of employing a series of lake management strategies to enhance production of endangered Snake River sockeye salmon (Oncorhynchus nerka) in its historical nursery lakes in central Idaho. We used a combination of limnological sampling, experimentation, and simulation modeling to assess effects of lake fertilization and kokanee reduction on growth and survival of juvenile sockeye salmon. Juvenile sockeye salmon from a broodstock of this endangered species are being introduced into the lakes from 1995 to 1998. Results of our analyses indicated that several lakes were suitable for receiving broodstock progeny. Field experimentation and simulation modeling indicated that lake fertilization, coupled with a program of kokanee reduction, provided the management option most likely to enhance the survival of stocked juvenile sockeye salmon. Simulation models that encompass physiological requirements, ecological interactions, and life-history consequences could be used as templates to help develop recovery plans for other endangered fishes.