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River ecosystems have been altered by flow regulation and species introductions. Regulated flow regimes often include releases designed to benefit certain species or restore ecosystem processes, and invasive species suppression programs may include efforts to restrict access to spawning habitat. The impacts of these management interventions are often uncertain. Here, we assess hypotheses regarding introduced brown trout (Salmo trutta) movement in a regulated river. We model mark- recapture data in a multistate framework to assess whether movement was affected by the operation of a tributary weir (restricting access to spawning habitat), experimental releases of fall-timed high flow experiments (Fall HFEs), or simply increased during the fall, spawning season. Our results suggest that the presence of the weir led to reduced tributary homing and the release of Fall HFEs stimulated upstream movement and straying. Both effects are of a similar magnitude, however the Fall HFE effect is more certain. Our results suggest the expansion of an invasive species was stimulated by management interventions, and demonstrate the potential for unanticipated outcomes of restoration in highly altered river ecosystems. Key words: ecological flows, designer flows, salmonids, adaptive management, invasion, barriers, Introduction River discharge regulation and water diversions that alter flow regimes and favor invasive fishes have led to the widespread homogenization of freshwater fish communities (Poff et al. 2007; Comte [...]

Trade‐offs among objectives in natural resource management can be exacerbated in altered ecosystems and when there is uncertainty in predicted management outcomes. Multi‐criteria decision analysis and value of information (VOI) are underutilized decision tools that can assist fisheries managers in handling trade‐offs and evaluating the importance of uncertainty. We demonstrate the use of these tools using a case study in the Sacramento River, California, USA, where two imperiled species with different temperature requirements, winter‐run Chinook Salmon Oncorhynchus tshawytscha and Green Sturgeon Acipenser medirostris, spawn and rear in the artificially cold Shasta Dam tailwater. A temperature‐control device installed on Shasta Dam maintains cool water for Chinook Salmon; however, uncertainties exist related to the effects of temperatures on the spawning and rearing of both species. We consider four alternative hypotheses in models of early life‐stage dynamics to evaluate the effects of alternative temperature management strategies on Chinook Salmon and Green Sturgeon management objectives. We used VOI to quantify the increase in management performance that can be expected by resolving hypothesis‐based uncertainties as a function of the weight assigned to species‐specific objectives. We found the decision was hindered by uncertainty; the best performing alternative depends on which hypothesis is true, with warmer or cooler alternative management strategies recommended when weights favor Green Sturgeon or Chinook Salmon objectives, respectively. The value of reducing uncertainty was highest when Green Sturgeon was slightly favored, highlighting the interaction between scientific uncertainty and decision makers' values. Our demonstration features multi‐criteria decision analysis and VOI as transparent, deliberative tools that can assist fisheries managers in confronting value conflicts, prioritizing resolution of uncertainty, and optimally managing aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Recovery of imperiled fishes can be achieved through suppression of invasives, but outcomes may vary with environmental conditions. We studied the response of imperiled desert fishes to an invasive brown (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) suppression program in a Colorado River tributary, with natural flow and longitudinal variation in thermal characteristics. We investigated trends in fish populations related to suppression and tested hypotheses about the impacts of salmonid densities, hydrologic variation, and spatial-thermal gradients on the distribution and abundance of native fish species using zero-inflated generalized linear mixed effects models. Between 2012 and 2018, salmonids declined 89%, and native fishes increased dramatically (~480%) once trout suppression surpassed ~60%. Temperature and trout density were consistently retained in the top models predicting the abundance and distribution of native fishes. The greatest increases occurred in warmer reaches and in years with spring flooding. Surprisingly, given the evolution of native fishes in disturbance-prone systems, intense, monsoon-driven flooding limited native fish recruitment. Applied concertedly, invasive species suppression and efforts to mimic natural flow and thermal regimes may allow rapid and widespread native fish recovery. Le retablissement d'especes de poissons en peril peut se faire par la suppression d'especes envahissantes, mais les resultats peuvent dependre des conditions ambiantes. Nous avons etudie la reaction de poissons de regions desertiques en peril a un programme de suppression des truites brunes (Salmo trutta) et des truites arc-en-ciel (Oncorhynchus mykiss) envahissantes dans un affluent du fleuve Colorado, en fonction de l'ecoulement naturel et des variations longitudinales des caracteristiques thermiques. Nous avons examine les tendances au sein de populations de poissons associees a la suppression et avons teste des hypotheses concernant les effets de la densite de salmonides, des variations hydrologiques et des gradients thermiques sur la repartition et l'abondance d'especes de poissons indigenes en utilisant des modeles lineaires generalises a effets mixtes avec inflation du zero. De 2012 a 2018, les salmonides ont connu une baisse de 89% et les poissons indigenes, une augmentation marquee (~480%) une fois que la suppression des truites a depasse ~60%. La temperature et la densite des truites etaient des variables uniformement retenues dans les modeles predisant le mieux l'abondance et la repartition de poissons indigenes. Les augmentations les plus importantes se sont produites dans les tronqons plus chauds et durant des annees d'inondations printanieres. Etonnamment, vu Devolution des poissons indigenes dans les systemes frequemment perturbes, des inondations intenses associees a la mousson limitaient le recrutement de poissons indigenes. Appliques de maniere concertee, la suppression d'especes envahissantes et des efforts visant a reproduire l'ecoulement et les regimes thermiques naturels pourraient permettre le retablissement rapide et repandu d'especes de poissons indigenes., Introduction Freshwater ecosystems are heavily modified world-wide, and consequently native fishes are threatened by a variety of persistent and emerging factors, including invasive species, hydropower generation and river regulation, climate [...]

Objective: Tributaries may play a vital role in maintaining populations of large river fishes, although the specific contributions of tributaries toward recruitment of river-wide populations are not often understood. Tributaries may experience fewer cumulative anthropogenic impacts relative to main-stem rivers and may offer more natural conditions supportive of native fish populations, which may provide opportunities for fish population restoration. Thus, an improved understanding of tributary-main-stem population dynamics may inform targeted conservation actions for spatially structured populations of large-river fishes. Colorado River tributaries in the Grand Canyon, Arizona, USA, are a focus of imperiled Humpback Chub Gila cypha conservation, which includes translocations to enhance population redundancy and to expand the overall population. However, the fate of fish dispersed to the main stem has not been thoroughly quantified. Methods: Using open population mark-recapture models, we quantified the relative contribution of three groups of Humpback Chub, including fish of confirmed tributary origin that were either translocated or produced in situ, and others presumed to be Colorado River main-stem-origin fish, to three main-stem populations. Our specific study objectives were to (1) estimate Colorado River abundances of tributary and main-stem-origin fish over time, (2) compare relative group-specific contributions to three main-stem populations, and (3) compare group-specific survival rates of Humpback Chub in the Colorado River and in a tributary where a recent translocation has occurred. Result: Tributaries contributed 26% and 43% of the overall abundance in two tributary inflow reach populations and zero in a third, which we attributed to uncharacteristically low tributary survival immediately following translocation. In the main stem, survival of tributary-origin fish was higher compared to main-stem-origin fish, suggesting an advantage of tributary residence. Conclusion: Our contrasting results from three different tributary inflow populations highlight the potential role for tributaries in sustaining large-river fish populations, which may have important implications for long-term maintenance of river metapopulations. [ABSTRACT FROM AUTHOR]

Invasive species can dramatically alter ecosystems, but eradication is difficult, and suppression is expensive once they are established. Uncertainties in the potential for expansion and impacts by an invader can lead to delayed and inadequate suppression, allowing for establishment. Metapopulation viability models can aid in planning strategies to improve responses to invaders and lessen invasive species' impacts, which may be particularly important under climate change. We used a spatially explicit metapopulation viability model to explore suppression strategies for ecologically damaging invasive brown trout (Salmo trutta), established in the Colorado River and a tributary in Grand Canyon National Park. Our goals were to estimate the effectiveness of strategies targeting different life stages and subpopulations within a metapopulation; quantify the effectiveness of a rapid response to a new invasion relative to delaying action until establishment; and estimate whether future hydrology and temperature regimes related to climate change and reservoir management affect metapopulation viability and alter the optimal management response. Our models included scenarios targeting different life stages with spatially varying intensities of electrofishing, redd destruction, incentivized angler harvest, piscicides, and a weir. Quasi‐extinction (QE) was obtainable only with metapopulation‐wide suppression targeting multiple life stages. Brown trout population growth rates were most sensitive to changes in age 0 and large adult mortality. The duration of suppression needed to reach QE for a large established subpopulation was 12 years compared with 4 with a rapid response to a new invasion. Isolated subpopulations were vulnerable to suppression; however, connected tributary subpopulations enhanced metapopulation persistence by serving as climate refuges. Water shortages driving changes in reservoir storage and subsequent warming would cause brown trout declines, but metapopulation QE was achieved only through refocusing and increasing suppression. Our modeling approach improves understanding of invasive brown trout metapopulation dynamics, which could lead to more focused and effective invasive species suppression strategies and, ultimately, maintenance of populations of endemic fishes. [ABSTRACT FROM AUTHOR]

A series of metallocarboranes were produced by reacting [NEt(sub 4)](sub 2)[Re(CO)(sub 3)Br(sub 3)] or [ReCO)(sub 3)(OH(sub 2))(sub 3)]Br with corresponding carbonates in preaence of aqueous solutions of either alkaline metal or tetraalkylammonium fluoride salts. In the course of the reactions it was discovered that Re metallocarvoranes could be directly prepared from the respective closo-clusters under similar reaction conditions used with nido-carboranes.

Abstract. -- The aquatic habitats of the Keechi Creek Wildlife Management Area in central east Texas were surveyed in May, June and August of 1999. A total of 34 species [...]

Diet interactions between native and non-native fishes may influence the establishment of native species within their historical range (i.e., reintroduction). Therefore, we illustrated the food web structure of and followed the transition of the federally endangered humpback chub Gila cypha into a novel food web following translocation and determined the potential for a non-native species, rainbow trout Oncorhynchus mykiss, to influence translocation success. Humpback chub and rainbow trout used resources high in the food web and assimilated similar proportions of native fishes, suggesting non-native rainbow trout may occupy an ecological role similar to humpback chub. Subsequently, humpback chub may be well suited to colonise tributaries because of their ability to consume resources high in the food web. Additionally, diet partitioning may occur between all members of the fish community as indicated by separation in trophic niche space and little trophic overlap; although all species, particularly bluehead sucker Catostomus discobolus, used a broad range of food resources. Rainbow trout stomach content analysis corroborated stable isotope analysis and suggested rainbow trout diet consisted of aquatic and terrestrial macroinvertebrates, while larger rainbow trout (>120 mm total length) consumed a greater proportion of fish (incidence of piscivory = 5.3%). Trophic interactions may reveal an underutilized niche space or biotic resistance to the establishment of translocated native fishes. Continued translocation of humpback chub into tributaries appears to be one option for conservation. However, successful establishment of humpback chub may depend on continued removal of non-native trout, increasing availability of diet sources at higher trophic levels. [ABSTRACT FROM AUTHOR]

Systematic larval fish surveys increase the probability of detecting rare species and provide ecological insights for more common species that can be difficult to infer from surveys of older life-stages. To characterize the reproductive success of the extant fish assemblage in the western Grand Canyon portion of the Colorado River, we conducted systematic larval fish surveys in 2014 and 2015. The effort identified endangered razorback sucker (Xyrauchen texanus) as initiating spawning in February with a continuation through July. We collected recently hatched protolarval fish throughout the study area including the most upstream sample sites, suggesting fish spawned throughout and upstream of the study area. Our collection of a protolarval endangered humpback chub (Gila cypha) supports the hypothesis that the population increased in range within the Grand Canyon from its dramatic 2001 contraction into the Little Colorado River and suggests localized spawning. Back-calculating hatching dates indicated humpback chub began hatching in late April and continued through mid-May. Native fishes numerically dominated larval fish collections (97.6 and 99.3% for 2014 and 2015, respectively) and recruitment to the early juvenile life-stage was documented for all fish species captured except razorback sucker. Abundance, measured as catch per unit effort and frequency of occurrence, was different between years for each native species captured (n = 5). Interannual differences in abiotic factors (discharge, diel fluctuations in discharge, and water temperature) were significantly different for most months between years. A redundancy analysis, evaluating the relationship between abiotic environmental factors and catch rates, suggested both discharge and water temperature were associated with speckled dace (Rhinichthys osculus), bluehead sucker (Catostomus discobolus), and flannelmouth sucker (Catostomus latipinnis), with a positive correlation to water temperature and a negative correlation to discharge. We were unable to identify associations between abiotic factors and the endangered fishes, which may have been due to the lack of variability in those species’ catch rates. Improving our understanding of the relationship between reproductive success and abiotic factors would enhance management of the system to benefit native fishes. [ABSTRACT FROM AUTHOR]