Geology topics

Research about Montana

Source-linked reports with geographic coverage including Montana.

At least 163 records · Page 9Linked to original sources

USGS2019

Glacier recession since the Little Ice Age: Implications for water storage in a Rocky Mountain landscape

Glacial ice is a significant influence on local climate, hydrology, vegetation, and wildlife. We mapped a complete set of glacier areas from the Little Ice Age (LIA) using very high-resolution satellite imagery (30-cm) within Glacier National Park, a region that encompasses over 400,000 hectares. We measured glacier change across the park using LIA glacier area as a baseline and used this to estimate change in glacier area and volume over time. An estimated 146 glaciers existed within the current boundaries of Glacier National Park during the LIA. By 2005, only 51 (35%) persisted. Nearly 90% of LIA glaciers had lost 50% of their area by 2005. This decrease in glacier area equates to an estimated loss of ice volume of 1.52 km3, or 1.37 km3 of water storage, roughly equivalent to 40% of Lake McDonald, the largest lake in the park. Understanding rates of deglaciation and implications for water storage and use can assist local resource managers and downstream communities in planning for change.

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USGS2019

Water-quality, bed-sediment, and biological data (October 2016 through September 2017) and statistical summaries of data for streams in the Clark Fork Basin, Montana

Water, bed sediment, and biota were sampled in selected streams from Butte to near Missoula, Montana, as part of a monitoring program in the Clark Fork Basin of western Montana. The sampling program was led by the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, to characterize aquatic resources in the Clark Fork Basin and emphasize trace elements associated with historic mining and smelting activities. Sampling sites were on the Clark Fork and selected tributaries. Water samples were collected periodically at 20 sites from October 2016 through September 2017. Bed-sediment and biota samples were collected once at 13 sites during August 2017. This report presents the analytical results and quality-assurance data for water-quality, bed-sediment, and biota samples collected at sites from October 2016 through September 2017. Water-quality data include concentrations of selected major ions, dissolved organic carbon, turbidity, nitrogen (nitrate plus nitrite), trace elements, and suspended sediment. Seasonal daily values of turbidity were determined at four sites. Bed-sediment data include trace-element concentrations in the fine-grained (less than 0.063 millimeter) fraction. Biological data include trace-element concentrations in whole-body tissue of aquatic benthic insects. Statistical summaries of water-quality, bed-sediment, and biological data for sites in the Clark Fork Basin are provided for the period of record.

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USGS2019

Improved detection of rare, endangered and invasive trout using a new large-volume sampling method for eDNA capture

Environmental DNA (eDNA) detection probability increases with volume of water sampled. Common approaches for collecting eDNA samples often require many samples since these approaches usually use fine filters, which restrict the volume of water that can be sampled. An alternative to collecting many, small volume water samples using fine filters may be to collect fewer, large volume water samples using coarse filters that do not clog as rapidly. We used mesocosm experiments and field evaluations to compare coarse filter‐large water volume samples (hereafter large volume filter samples) versus fine filter‐small water volume samples (hereafter small volume filter samples) for detection and quantification of rainbow trout ( Oncorhynchus mykiss ) and bull trout ( Salvelinus confluentus ) DNA. We found that large volume filter sampling can be an effective approach for detecting DNA of low‐density target taxa. In mesocosm experiments, large‐volume and small‐volume water samples detected similar quantities of rainbow trout DNA. In the field, large volume samples more frequently detected bull trout DNA, had higher bull trout DNA copy number, and higher total DNA concentrations than small volume samples. However, sampling higher water volumes increased the potential for PCR inhibition so the DNA workflow had to be altered for large volume samples. Combining larger water volume samples with other strategies, like increasing PCR sensitivity and the number of PCR replicates, will improve detection of rare species, which is crucial for advancing conservation and ecological understanding.

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USGS2019

Microbial assemblages reflect environmental heterogeneity in alpine streams

Alpine streams are dynamic habitats harboring substantial biodiversity across small spatial extents. The diversity of alpine stream biota is largely reflective of environmental heterogeneity stemming from varying hydrological sources. Globally, alpine stream diversity is under threat as meltwater sources recede and stream conditions become increasingly homogeneous. Much attention has been devoted to macroinvertebrate diversity in alpine headwaters, yet to fully understand the breadth of climate change threats, a more thorough accounting of microbial diversity is needed. We characterized microbial diversity (specifically Bacteria and Archaea) of 13 streams in two disjunct Rocky Mountain subranges through 16S rRNA gene sequencing. Our study encompassed the spectrum of alpine stream sources (glaciers, snowfields, subterranean ice, and groundwater) and three microhabitats (ice, biofilms, and streamwater). We observed no difference in regional (γ) diversity between subranges but substantial differences in diversity among (β) stream types and microhabitats. Within‐stream (α) diversity was highest in groundwater‐fed springs, lowest in glacier‐fed streams, and positively correlated with water temperature for both streamwater and biofilm assemblages. We identified an underappreciated alpine stream type—the icy seep—that are fed by subterranean ice, exhibit cold temperatures (summer mean <2°C), moderate bed stability, and relatively high conductivity. Icy seeps will likely be important for combatting biodiversity losses as they contain similar microbial assemblages to streams fed by surface ice yet may be buffered against climate change by insulating debris cover. Our results show that the patterns of microbial diversity support an ominous trend for alpine stream biodiversity; as meltwater sources decline, stream communities will become more diverse locally, but regional diversity will be lost. Icy seeps, however, represent a source of optimism for the future of biodiversity in these imperiled ecosystems.

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USGS2019

Planning for ecological drought: Integrating ecosystem services and vulnerability assessment

As research recognizes the importance of ecological impacts of drought to natural and human communities, drought planning processes need to better incorporate ecological impacts. Drought planning currently recognizes the vulnerability of some ecological impacts from drought (e.g., loss of instream flow affecting fish populations). However, planning often does not identify all the ecological aspects in a landscape that stakeholders value, nor does it examine the extent to which those aspects are vulnerable to drought. One approach for identifying ecological aspects is ecosystem services (ES) -- i.e., the benefits humans receive from nature. To incorporate ecological impacts into drought planning in the Upper Missouri Headwaters region (Montana, USA), we combined ES elicitation using the Common International Classification of Ecosystem Services and a vulnerability assessment using semi-structured interviews. We juxtaposed results from the interviews and the ES elicitation to assess which ES might be vulnerable to drought and which impacts from interviews were associated with losses of ES. While both methods suggested common drought vulnerabilities, each method also suggested drought vulnerabilities not reported using the other method. The ES elicitation produced more detail about services present in the UMH ecosystem today while interviews resulted in more discussion about ecological transformation from future droughts. Results suggest that some combination of open-ended vulnerability assessment methods and ES elicitation using a structured framework can result in greater understanding of ecological drought vulnerability in a given region.

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USGS2019

Modeling elk‐to‐livestock transmission risk to predict hotspots of brucellosis spillover

Wildlife reservoirs of infectious disease are a major source of human‐wildlife conflict because of the risk of potential spillover associated with commingling of wildlife and livestock. In the Greater Yellowstone Ecosystem, the presence of brucellosis ( Brucella abortus ) in free‐ranging elk ( Cervus canadensis ) populations is of significant management concern because of the risk of disease transmission from elk to livestock. We identified how spillover risk changes through space and time by developing resource selection functions using telemetry data from 223 female elk to predict the relative probability of female elk occurrence daily during the transmission risk period. We combined these spatiotemporal predictions with elk seroprevalence, demography, and transmission timing data to identify when and where abortions (the primary transmission route of brucellosis) were most likely to occur. Additionally, we integrated our predictions of transmission risk with spatiotemporal data on areas of potential livestock use to estimate the daily risk to livestock. We predicted that approximately half of the transmission risk occurred on areas where livestock may be present (i.e., private property or grazing allotments). Of the transmission risk that occurred in livestock areas, 98% of it was on private ranchlands as opposed to state or federal grazing allotments. Disease prevalence, transmission timing, host abundance, and host distribution were all important factors in determining the potential for spillover risk. Our fine‐resolution (250‐m spatial, 1‐day temporal), large‐scale (17,732 km 2 ) predictions of potential elk‐to‐livestock transmission risk provide wildlife and livestock managers with a useful tool to identify higher risk areas in space and time and proactively focus actions in these areas to separate elk and livestock to reduce spillover risk.

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USGS2019

Mapping a keystone shrub species, huckleberry (Vaccinium membranaceum), using seasonal colour change in the Rocky Mountains

Black huckleberries ( Vaccinium membranaceum ) provide a critical food resource to many wildlife species, including apex omnivores such as the grizzly bear ( Ursus arctos ), and play an important socioeconomic role for many communities in western North America, especially indigenous peoples. Remote sensing imagery offers the potential for accurate landscape-level mapping of huckleberries because the shrub changes colour seasonally. We developed two methods, for local and regional scales, to map a shrub species using leaf seasonal colour change from remote sensing imagery. We assessed accuracy with ground-based vegetation surveys. The high-resolution supervised random forest classification from one-meter resolution National Agricultural Imagery Program (NAIP) imagery achieved an overall accuracy of 75.31% (kappa = 0.26). The approach using multi-temporal 30-meter Landsat imagery similarly had an overall accuracy of 79.19% (kappa = .31). We found underprediction error was related to higher forest cover and a lack of visible colour change on the ground in some plots. Where forest cover was low, both models performed better. In areas with <10% forest cover, the high-resolution classification achieved an accuracy of 80.73% (kappa = 0.48), while the Landsat model had an accuracy of 82.55% (kappa = 0.47). Based on the fine-scale predictions, we found that 94% of huckleberry shrubs identified in our study area of Glacier National Park, Montana, USA are over 100 meters from human recreation trails. This information could be combined with productivity and phenology information to estimate the timing and availability of food resources for wildlife and to provide managers with a tool to identify and manage huckleberries. The development of the multi-temporal Landsat models sets the stage for assessment of impacts of disturbance at regional scales on this ecologically, culturally, and economically important shrub species. Our approach to map huckleberries is straightforward, efficient and accessible to wildlife and environmental managers and researchers in diverse fields.

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USGS2019

Elk forage and risk tradeoffs during the fall archery season

During late summer and fall, elk ( Cervus canadensis ) need access to adequate nutrition to support physiological requirements for reproduction and overwinter survival. The archery hunting season often occurs during this period and can affect distributions of elk as they seek areas that minimize perceived harvest risk. Areas that confer lower harvest risk may provide relatively low‐value nutrition, resulting in a potential tradeoff between minimizing risk and accessing adequate forage. We used radio‐collar data collected from female elk during late summer and fall (Aug–Oct) and estimated resource selection models to evaluate the extent of this potential risk‐nutrition tradeoff. To evaluate if elk exposed to a greater hunting risk altered selection for forage resources, we assessed the relationship between individuals’ selection coefficients for forage and the proportion of their late‐summer‐fall home range accessible to hunters (our metric of hunting risk). Our results indicate that during the archery season, elk with higher‐risk home ranges selected more strongly for areas farther from motorized routes than elk with lower‐risk home ranges. Regardless of the level of risk, however, elk maintained or increased selection for areas with higher forage quality, suggesting that elk did not compromise access to nutritional resources during the archery season. Elk with higher‐risk home ranges were also exposed to the poorest nutrition and increased their selection for areas with higher forage quality more strongly than elk with lower‐risk home ranges during the hunting season. Elk with lower‐risk home ranges had access to the highest nutrition, which may be due to the availability of concentrated sources of high‐quality forage from irrigated agricultural areas on private lands that restricted hunter access. Resource agencies interested in encouraging elk to remain on public lands during the hunting seasons might consider closing motorized travel during the archery season to increase security on public lands, limiting hunter pressure on public lands, improving forage quality on public lands, and working with private land owners to enhance hunter accessibility and restrict elk access to high‐quality forage resources.

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USGS2019

Dynamic relations for the deposition of sediment on floodplains and point bars of a freely-meandering river

Fluvial features such as floodplains and point bars are built by sediment deposition and sculpted by erosion. Long-term measurements (38 yr) of the cross-section topography of active floodplains and point bars along the freely-meandering Powder River in southeastern Montana, USA (mean daily discharge of 12.5 m 3 s −1 ), were used to develop dynamic relations between annual sediment deposition and peak-flood discharge. Five floodplain sections and five point-bar sections were selected from 24 cross sections along a 90-km study reach. At each cross section the sediment deposition volume per unit streamwise distance was computed as the difference between two topographic surveys made in consecutive years. Snowmelt floods were found to be the dominant annual process. However, other processes such as flash floods, ice breakup floods, and autumnal floods were important episodically. The dynamic relations were linear for both fluvial features. The snowmelt deposition-discharge relations showed, in general, that point bars were about two times more efficient at trapping sediment than floodplains. Each relation had a discharge threshold that must be exceeded before sediment was deposited. Although these discharge thresholds for floodplains and point bars had essentially the same mean value (69 and 71 m 3 s −1 , respectively), they represented different processes. Thresholds for other rivers will probably differ from those for Powder River because of different channel geometry and sediment characteristics.

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USGS2019

Predicting attenuation of salinized surface- and groundwater-resources from legacy energy development in the Prairie Pothole Region

Oil and gas (energy) development in the Williston Basin, which partly underlies the Prairie Pothole Region in central North America, has helped meet U.S. energy demand for decades. Historical handling and disposal practices of saline wastewater co-produced during energy development resulted in salinization of surface and groundwater at numerous legacy energy sites. Thirty years of monitoring (1988–2018) at Goose Lake, which has been producing since the 1960s, documents long-term spatial and temporal changes in water quality from legacy energy development. Surface water quality was highly variable and decoupled from changes in groundwater quality, likely due to annual and regional climatic fluctuations. Therefore, changes in surface water-quality were not considered a reliable indicator of subsurface chloride migration. However, chloride concentrations in monitoring wells near wastewater sources exhibited systematic temporal reductions allowing for estimates of the time required for natural attenuation of groundwater to U.S. Environmental Protection Agency acute and chronic chloride toxicity benchmarks and a local background level. Point attenuation rates differed based on sediment type (outwash vs till) and yielded a range of predicted years when water-quality targets will be reached: acute – 2045 to 2113; chronic – 2069 to 2160; background – 2126 to 2275. Bulk attenuation rates from four separate years of data were used to calculate the distances chloride could migrate downgradient from the largest wastewater source. Potential distances of downgradient migration before dilution to water-quality targets decreased from 1989 to 2018: acute – 949 to 673 m; chronic – 1220 to 922 m; background – 1878 to 1525 m. Several downgradient wetlands are within these distances and will continue to receive saline contaminated groundwater for years. While these results demonstrate chloride attenuation at a legacy energy site, they also highlight the persistence of saline wastewater contamination and the need to mitigate future spills to prevent long-term salinization from energy development.

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USGS2019

Native forage mediates influence of irrigated agriculture on migratory behaviour of elk

Ungulates migrate to maximize nutritional intake when forage varies seasonally. Populations of ungulates often include both migratory and non-migratory individuals, but the mechanisms driving individual differences in migratory behaviour are not well-understood. We quantified associations between hypothesized drivers of partial migration and the likelihood of migration for individual ungulates that experienced a range of environmental conditions and anthropogenic influences. We evaluated the effects of forage variation, conspecific density, and human land uses on migratory behaviour of 308 adult female elk in 16 herds across western Montana. We found irrigated agriculture on an individual's winter range reduced migratory behaviour, but individuals were more likely to migrate away from irrigated agricultural areas if better forage was available elsewhere or if they experienced high conspecific density on their winter range. When the forage available during the summer growing season varied predictably between years, elk were more likely to migrate regardless of whether they had access to irrigated agriculture. Our study shows that predictable availability of beneficial native forage can encourage migration even for ungulates with irrigated agriculture on their winter range. Perturbations that can affect the forage available to ungulates include wildfires, timber harvest, livestock grazing and changing weather patterns. If these or other disturbances negatively affect forage on summer ranges of migrants, or if they cause forage to vary unpredictably across space and time, our results suggest migratory behaviour may decline as a result.

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USGS2019

Application of multistate modeling to estimate salmonid survival and movement in relation to spatial and temporal variation in metal exposure in a large mining-impacted river

We used telemetry and multistate modeling to estimate survival and movement of brown trout Salmo trutta and westslope cutthroat trout Oncorhynchus clarkii lewisi in relation to dissolved copper concentrations in 189 km of the upper Clark Fork River, Montana, a mining-impacted river in western Montana. Annual survival estimates for both brown trout (range, 0.27-0.53) and westslope cutthroat trout (range, 0.001-0.34) over the three-year study were low and variable within the study area, with survival negatively related to level of copper exposure. Survival probability for brown trout and westslope cutthroat trout in the uppermost river segment, where dissolved copper concentrations frequently exceeded acute criteria for aquatic life (range, 31-60 d >13.4 µg·L-1), was 2.1 times and 122 times lower, respectively, compared to survival rates in the lowermost segment that had relatively low dissolved copper (0 d exceedance of acute concentration). Seasonal differences in survival also appeared to be related to copper exposure level. Lowest survival for both species occurred in the spring-summer period when dissolved copper concentrations were elevated coincident with higher discharge. Movement among study segments was generally low, and cutthroat trout in particular showed low movement into the uppermost river segment with the most elevated copper levels. Both species showed high rates of movement into tributaries, which coincided with their respective spawning migrations rather than as an apparent avoidance of elevated copper levels. Our research design provided an uncommon opportunity to directly relate the degree of contaminant exposure to estimates of fish survival and movement at a population-level over a large spatial scale. This linkage between survival rate and level of copper exposure for both brown trout and cutthroat trout in the upper Clark Fork River suggests that additional removal of tailings deposits could improve survival rates.

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USGS2019

Using environmental DNA to extend the window of early detection for dreissenid mussels

Tools that bolster early detection of invasive species are needed to prevent their spread. In this study, we assessed if environmental DNA (eDNA) can extend the seasonal window for dreissenid mussel early detection beyond that of plankton tows, which are limited to warmer seasons when mussel larvae are present. We focused eDNA sampling efforts at multiple sites in Tiber Reservoir (Montana) where dreissenid mussel abundance is hypothesized to be low. Samples were collected in June and October 2017, when water temperatures were cooler than thermal optima for dreissenid reproduction, and in July 2017 when water temperatures were warmer and conducive for reproduction. We detected dreissenid mussel DNA in June, July and October even though no dreissenid mussels were observed using non-molecular tools in 2017. A subset of positive and negative eDNA samples were analyzed by an independent lab and results were corroborated. We then estimated the effort needed for 95% probability detection of dreissenid DNA at each site within Tiber Reservoir and found that as many as 27, 14, and 34 samples needed to be collected in June, July and October, respectively. To further validate the utility of eDNA, we also present ancillary eDNA results from other waters in the Flathead Reservation (Montana) where dreissenid mussels have never been detected and from waters with established zebra mussel populations in the upper Mississippi River, which were sampled in the spring when water temperatures were cooler than thermal optima for dreissenid reproduction. All Flathead Reservation samples were negative for dreissenid mussel DNA, while all upper Mississippi River samples were positive. This study adds to a growing body of research that demonstrates eDNA is a highly sensitive tool for dreissenid mussel surveillance in newly invaded waters, including colder seasons when non-molecular tools are likely to be less effective or more challenging to employ.

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USGS2019

Keeping the crown of the continent connected: An interagency US2 connectivity workshop report

At over 2.5 million acres, Glacier National Park and the Bob Marshall Wilderness complex form one of the largest protected areas in the continental United States. Straddling the Continental Divide, these two areas form a vital linkage between vast areas of public land to the south towards Yellowstone, and contiguous protected areas north of the US-Canada border. However, US Highway 2 (US2) and the Burlington Northern-Santa Fe (BNSF) railroad separate Glacier National Park to the north from the Bob Marshall Wilderness complex to the south. While this narrow ribbon of development passes through primarily public land, it is bordered in some areas by narrow strips of private land. Many of these private parcels are developed as ranches, campgrounds, or seasonal and permanent home sites and businesses. Currently, two of the defining characteristics of this portion of the US2 corridor are relatively low highway traffic volume, but relatively high railroad traffic volume. The highway had a 2017 annual average daily traffic volume (AADT) of 1859 vehicles, far less than other interstate highways around the region which often have AADTs well over 10,000. Conversely, the BNSF railroad line currently carries about 33 trains per day, making it one of the busier railroad lines in the northwestern US. While wildlife movement patterns across this corridor have not been well studied, the existing data suggests that wildlife can still make frequent and successful crossings at current railroad and highway traffic levels. However, as the region’s human population grows, we expect that connectivity to diminish. Over the past decade (2000-2017), based on census data, Flathead County has grown by 10% and Glacier County has grown by 1.5%. A study on loss of open space found that Flathead County alone accounts for 15% of the new homes built in Montana since 2000 (https://headwaterseconomics.org/economicdevelopment/local-studies/montana-home construction/). Outdoor recreation and tourism have also been breaking participation records (source: GPI record passengers https://flatheadbeacon.com/2018/01/24/glacier-park-international-airport-sees-record-passengers-2017/, GNP record visitation https://www.usnews.com/news/best-states/montana/articles/2018-01 15/glaciernational-park-breaks-visitation-record-in-2017). This growth has been accompanied by a ~50% increase in highway traffic volume in the corridor over the past decade (Waller and Miller 2015). This increased traffic is decreasing the time available for wildlife to cross the highway and appears to be increasing the frequency of wildlife killed by vehicles (Fig. 1 and 2). In addition, the Middle Fork of the Flathead River is a favored river for recreation, and this also appears to be growing. In the summer of 2017, researchers recorded 136 boats per day in July and 93 boats per day in August. Although the river does not extend along the entire highway, it extends along 31 miles of the highway corridor.

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USGS2019

Monitoring brine contamination using time-lapse airborne electromagnetic surveys, East Poplar Oil Field, Montana

Integrated geophysical and water-quality studies have been used to delineate areas of saline groundwater in shallow unconfined aquifers underlying the East Poplar oil field in northeastern Montana. In 2004, a RESOLVE survey was conducted over the oil field to identify high conductivity areas potentially associated with brine contamination and to map the shale unit comprising the base of aquifer. In 2014, a SkyTEM 301 survey was conducted over the same flight paths to examine possible changes in groundwater conductivity and to complete the base-of-aquifer mapping where the depth of investigation from the 2004 survey was inadequate. We present a preliminary comparison between the 2004 and 2014 surveys.

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USGS2018

Spatiotemporal analysis of the Foreshock-Mainshock-Aftershock sequence of the 6 July 2017 M5.8 Lincoln, Montana, earthquake

A MW 5.8 earthquake occurred on 6 July 2017 at 12.2 km depth, 11 km southeast of Lincoln in west central Montana. No major damage or injuries were reported; however, the widely felt mainshock generated a prolific aftershock sequence with more than 1200 located events through the end of 2017. The Lincoln event is the latest in a series of moderate-to-large earthquakes that have affected western Montana. We characterize the spatiotemporal evolution of the sequence using matched filter detection and multiple-event relocation techniques. Moment tensor solutions and aftershock locations indicate faulting occurred on a 9-km-long NNE-striking, near-vertical, strike-slip fault antithetic to the Lewis and Clark Line, the main through-going fault system. Seismicity primarily occurs between 6 and 16 km depth, consistent with seismicity in the Intermountain Seismic Belt. We estimate a fault rupture area of ~64 km2 and ~30 cm of average fault displacement. We identified four foreshocks in the three days prior to, and 3005 aftershocks in the three weeks following the mainshock. The supplemented catalog frequency-magnitude distribution has a b-value of 0.79 and a minimum magnitude of completeness of 0.7. The overall decay rate is consistent with a modified Omori decay law p-value of 0.76 and c-value of 0.32. This event demonstrates that unmapped faults antithetic to major geologic structures play a role in accommodating regional strain in Western Montana and can host significant earthquakes

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USGS2018

Impacts of nonnative Brown Trout on Yellowstone Cutthroat Trout in a tributary stream

Nonnative trout are a considerable threat to native salmonids, yet our understanding of the mechanisms behind interspecific interactions remains limited. We evaluated the impacts of nonnative Brown Trout Salmo salar on a population of Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in Montana. We contrasted diets, growth, and survival of Yellowstone Cutthroat Trout occurring in allopatry (i.e., where no Brown Trout were present) with individuals sympatric (i.e., co‐occurring) with nonnative Brown Trout. We assessed summer and autumn diets using gastric lavage methods and survival and growth using mark–recapture analyses. Overlap in diets at sites where Yellowstone Cutthroat Trout were sympatric with Brown Trout was high during July (Horn's index: H = 0.94) and October ( H = 0.83). In the presence of Brown Trout, Yellowstone Cutthroat Trout growth rates were significantly lower for juvenile (<175 mm) length and adult (≥175 mm) length and mass than in allopatric sites. Allopatric Yellowstone Cutthroat Trout survival was greater across size‐classes; the most pronounced difference was in the age‐2 size‐class (125–175 mm). Together, these results in concert with observed changes in length‐frequency data, indicating a considerable lack of Yellowstone Cutthroat Trout recruitment where they are sympatric with Brown Trout, suggest the negative implications of Brown Trout are notable.

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USGS2018

Land management alters traditional nutritional benefits of migration for elk

Ungulates typically migrate to maximize nutritional intake when forage varies seasonally. In western North America, however, increasing numbers of ungulates reside on low-elevation winter range year-round rather than migrating. These residents often occupy irrigated agricultural areas, but it is not known whether the nutrition provided by agricultural land exceeds that gained by migration. We evaluated the nutrition available to a partially migratory population of elk ( Cervus canadensis ) in west-central Montana where some individuals summered on low-elevation agricultural lands, whereas others summered on traditional higher-elevation ranges. We sampled elk forage plants from ground plots and adult female elk movements from global positioning system (GPS) collar locations during late summer for 2 years. We tested for differences in the nutrition provided by 11 vegetative communities commonly available to elk in the Rocky Mountains and the nutrition available in areas used by individuals whose behaviors ranged from residency to migration. We found the nutrition available to elk decreased along the continuum from resident to migratory behavior, contrary to our hypothesis that all behaviors would provide access to equivalent forage quality. The relatively small summer home ranges of migrants suggest other factors (e.g., decreased competition) may compensate for their lower nutritional value, because the size of a home range is often inversely related to its fitness benefits. We found irrigated agriculture provided the highest forage quality in low elevations, but recently burned (1–6 yr prior) dry forests at higher elevations provided forage quality approximately equivalent to that of irrigated agriculture. Excluding elk from irrigated agricultural areas should therefore reduce nutritional incentives for elk to reside at low elevations year-round. Additionally, fire in higher-elevation dry forests may temporarily increase forage quality for elk and improve nutritional benefits of migratory behavior. Our results indicate land management practices can affect nutritionally mediated fitness benefits of differing behaviors in partially migratory populations of ungulates

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