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Beaver (Castor canadensis) translocation and mimicry is an increasingly popular tool for process-based restoration of degraded streams. Processes influenced by beaver restoration include stream-floodplain connectivity, multi-threaded channel formation, enhanced riparian condition and fire resiliency, and streamflow attenuation. Beaver activity can also be a nuisance in agricultural settings, increase invasive species abundance, and create in-stream barriers to fish. Previous studies indicate that spring-spawning salmonid species can pass beaver dams in higher proportions than fall-spawning species. Thus, restoration or mimicry of beavers in streams containing fall-spawning, threatened Bull Trout (Salvelinus confluentus) is of concern to many biologists. We evaluated Bull Trout passage at beaver dams in two Montana streams: Meadow Creek (East Fork Bitterroot River drainage) in summer 2020 and Morrison Creek (Middle Fork Flathead River drainage) from 1997 to 2011. In Meadow Creek, 16% of PIT-tagged Bull Trout which entered a large beaver dam complex were detected upstream of some dams, but no fish moved through the entire 1 km complex. In Morrison Creek, redds were more likely than random to be located below dams, but two or more redds were found upstream of at least one dam in 6 of 9 years dams were present. These results suggest that beaver dams can affect the movement of Bull Trout, but that passage depends on the characteristics of individual dams and reach geomorphology. Our methods cannot distinguish between inhibition of fish movement and selection of beaver-created habitats by fish. Therefore, we suggest future research on beaver restoration in streams with Bull trout.

Nonnative fish eradication via the piscicide rotenone is an effective tool for fisheries management and conservation of native species. However, the long-term effects on nontarget organisms, including benthic invertebrates and zooplankton in alpine lakes, are understudied and are poorly understood. As part of a landscape-scale native fish conservation project, we assessed the effects of 50 ppb of rotenone on the aquatic invertebrate community by comparing pre- and postrotenone treatment density and diversity metrics of benthic invertebrates and zooplankton in 13 alpine lakes and their outlets in Montana, USA. Across study sites, decreases in density and diversity of some invertebrate taxa, including Ephemeroptera, Plecoptera, and Trichoptera, were observed the year following rotenone treatment, and within 3 y, densities and diversities were similar to and sometimes higher than pretreatment values. These results demonstrate resilience of aquatic invertebrate communities following rotenone exposure in alpine lakes and streams and informs fisheries managers for planning rotenone projects and monitoring recovery of nontarget organisms. Additional studies will be useful to evaluate the mechanisms driving invertebrate recovery rates, including downstream drift from nontreated areas and terrestrial adult dispersal.

Stream habitat changes affecting primary consumers often indirectly impact secondary consumers such as fishes. Blooms of the benthic algae Didymosphenia geminata (Didymo) are known to affect stream macroinvertebrates, but the potential indirect trophic impacts on fish consumers are poorly understood. In streams of the Kootenai River basin, we quantified the diet, condition, and growth rate of species of trout, char, and sculpin. In 2018, macroinvertebrate taxa composition was different between a stream with Didymo and a stream without, but trout diets, energy demand, and growth rates were similar. Trout abundance was higher in the stream with Didymo, but the amount of drifting invertebrates was higher in the stream without. In 2019, we surveyed 28 streams with a gradient of coverage. Didymo abundance was correlated only with the percentage of aquatic invertebrates in trout diets and was not related to diets of char or sculpin or condition of any species. Thus, we found no evidence for a trophic link between Didymo blooms and the condition or growth of trout, char, or sculpin in mountainous headwater streams.

The spread of non-native fish species is a common problem in lakes and streams worldwide. Species that establish viable populations in a new environment can seriously deplete populations of native species and desired sportfishes. In some instances, extirpation of a native species has occurred. In western North America, the most common avenue by which non-native species invade new waterbodies is illegal stocking by anglers, aquaculturists, and others. Thus, preventing further illegal fish introductions is of the utmost importance for native aquatic species. Using data collected by state agency personnel from 1953 to 2015, we examined multiple social and physical variables to determine the factors that best explain which lakes in northwestern Montana had past illegal fish introductions. An equation using elevation, surrounding population, and fishing pressure was found to best fit the data. This equation was then used to calculate an index of the vulnerability of lakes within the region to future illegal fish introductions. The techniques used in this study have broad applicability that can be used in many regions with illegal fish introductions, and ultimately help to alleviate the problem.

Native fish populations have continued to decline worldwide despite advances in management practices. As such, new approaches are needed to complement the old. In many flowing and standing waters, larval amphibians are the dominant vertebrate taxa. This can be important to fisheries due to amphibians’ ability to influence macroinvertebrate communities, alter benthic habitat, and supply nutrients in aquatic systems. These changes can, in turn, affect the ecology and fitness of other aquatic organisms such as fishes. Due to their large effects in some systems, it is suggested that fisheries managers carefully consider actions that may affect amphibian populations and actively conserve them in some cases. Preservation of riparian areas and amphibian-associated microhabitats may even be used as a tool to positively impact freshwater fisheries by conserving amphibians that help maintain aquatic systems. Therefore, knowledge of local amphibian life histories and behaviors may be important in conserving associat...

The tick-borne flaviviruses (TBFV) occur worldwide and the tick-borne encephalitis virus (TBEV) members of the group often cause severe, debilitating neurological disease in humans. Although the primary route of infection is through the bite of an infected tick, alimentary infection through the consumption of TBEV-contaminated dairy products is also well-documented and is responsible for some disease in endemic areas. Experimental infection of goats, cattle, and sheep with TBEV shows that the virus can be excreted in the milk of infected animals. Additionally, the virus remains infectious after exposure to low pH levels, similar to those found in the stomach. To evaluate the survival of virus in milk, we studied the stability of the BSL-2 TBFV, Langat virus, in unpasteurized goat milk over time and after different thermal treatments. Virus was stable in milk maintained under refrigeration conditions; however, there was a marked reduction in virus titer after incubation at room temperature. High temperature, short time pasteurization protocols completely inactivated the virus. Interestingly, simulation of a typical thermal regime utilized for cheese did not completely inactivate the virus in milk. These findings stress the importance of proper milk handling and pasteurization processes in areas endemic for TBEV.