Geology topics

Alexander V. Zale

Publications and source records attributed to Alexander V. Zale.

At least 19 recordsLinked to original sources

USGS2024

Spatial and temporal variability of movements among sympatric salmonids in an unfragmented inland watershed

Objective Our aim was to determine the movement patterns of three abundant salmonids—Brown Trout Salmo trutta , Mountain Whitefish Prosopium williamsoni , and Rainbow Trout Oncorhynchus mykiss —in the Smith River watershed of Montana. Methods We tagged 7172 fish with passive integrated transponder (PIT) tags, monitored their movements past 15 stationary PIT arrays over 4 years, and located tagged fish between arrays by conducting mobile surveys. Result Movement patterns varied seasonally, among species, and among locations. Movement was greatest in the middle portion of the watershed, which included a pristine main‐stem canyon and lower reaches of major tributaries. Fish rarely left the canyon, but movement into the canyon from other regions was common. Mountain Whitefish were most likely to move, and Brown Trout were least likely to move. Most fish travelled less than 10 km, but some fish travelled over 100 km. Distinct movement patterns were not evident; rather, a continuous spectrum of movement behaviors was apparent. Movements by Mountain Whitefish and Rainbow Trout increased during their spawning periods. Movements peaked when mean daily water temperatures were between 11.3 and 17.1°C. Conclusion Movements were diverse and probably contributed to metapopulation dynamics, population resiliency, and species diversity. Fish movements along stream networks connect populations across diverse landscapes, and therefore, protecting and restoring stream connectivity along inland streams such as the Smith River is critical to maintaining productive fish assemblages.

Montana↗

USGS2023

Synthesis of climate and ecological science to support grassland management priorities in the North Central Region

Grasslands in the Great Plains are of ecological, economic, and cultural importance in the United States. In response to a need to understand how climate change and variability will impact grassland ecosystems and their management in the 21st century, the U.S. Geological Survey North Central Climate Adaptation Science Center led a synthesis of peer-reviewed climate and ecology literature relevant to grassland management in the North Central Region (including Montana, Wyoming, Colorado, North Dakota, South Dakota, Nebraska, and Kansas). This synthesis was done to begin to address grassland managers’ information needs and identify research gaps. This open-file report summarizes the impacts of climate change and variability on temperature, water availability, wildfire, vegetation, wildlife, large-bodied ruminants, grazing, and land-use change and the implications for grassland management in the North Central region. This open-file report also identifies areas in which further research is needed. U.S. Geological Survey funded this project.

Colorado, Kansas, Montana, Nebraska, North Dakota,↗

USGS2023

Diet composition and resource overlap of sympatric native and introduced salmonids across neighboring streams during a peak discharge event

Species assemblages composed of non-native and native fishes are found in freshwater systems throughout the world, and interactions such as interspecific competition that may negatively affect native species are expected when non-native species are present. In the Smith River watershed, Montana, rainbow trout were introduced by 1930. Native mountain whitefish and non-native rainbow trout have presumably occurred in sympatry since the introduction of rainbow trout; however, knowledge about how these two species compete with one another for food resources is sparse. We quantified diet compositions of rainbow trout and mountain whitefish in the mainstem Smith River and in a tributary to the Smith River—Sheep Creek—to determine the degree of overlap in the diets of mountain whitefish and rainbow trout in the Smith River and between the mainstem Smith River and a tributary stream. Rainbow trout and mountain whitefish had generalist feeding strategies, which probably contribute to the amicable coexistence of these species. Diet overlap between rainbow trout and mountain whitefish was high (Pianka’s index value = 0.85) in the Smith River and moderate in Sheep Creek (Pianka’s index value = 0.57). Despite overlap in diets, some resource partitioning may alleviate resource competition (e.g., rainbow trout consumed far more Oligochaeta than mountain whitefish but fewer Brachycentridae and Chironomidae). Diet composition of rainbow trout and mountain whitefish did not differ greatly between the Smith River and Sheep Creek. Prey categories most commonly used by mountain whitefish at the population and individual levels (i.e., Ephemeroptera and Trichoptera) are sensitive taxa and many species within these orders have experienced extinctions and population declines. Therefore, future changes in resource availability or competition could be of concern.

Montana↗

USGS2023

Aerial application of organic pellets eliminates Lake Trout recruitment from a primary spawning reef in Yellowstone Lake

Invasive Lake Trout Salvelinus namaycush in the Yellowstone Lake ecosystem have been gillnetted since 1995 to suppress the population and allow for recovery of native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri . Although gillnetting is effective (Lake Trout population growth rate λ ≤ 0.6 during 2012–2022), the effort only targets free-swimming, age-2 and older Lake Trout. We developed a complementary suppression method using organic (soy and wheat) pellets to cause Lake Trout embryo mortality and reduce recruitment from spawning areas. The entire Carrington Island spawning reef (0.5 ha) was aerially treated with 3.56 and 3.00 kg/m 2 of pellets in 2019 and 2020, respectively. Pellet decomposition caused dissolved oxygen concentrations to decline to lethal levels at 20 cm depth in the substrate, and pellets mostly dissipated from the reef within 12 d. Lake Trout fry trap CPUE was reduced to zero after ice-off each spring after the treatments. Prior to the treatments, 71 fry were captured during 58 trap-nights of effort in 2017–2019. After the treatments, no fry were captured during 273 trap-nights in 2020 and 2021. Lake Trout CPUE in large-mesh gill nets set near Carrington Island in September did not decline during 2017–2021 and fry were again trapped on the reef in spring 2022, suggesting that adults were not deterred from spawning there in the years after the pellet treatments. Complementary methods that increase mortality of prerecruits may allow for a reduction in gill-netting effort and the long-term costs of maintaining Lake Trout population suppression in Yellowstone Lake. Treatment of spawning areas may improve suppression efficiency for Lake Trout and invasive fish populations elsewhere because entire cohorts are targeted while immobile and temporarily concentrated in relatively small areas.

Wyoming↗

USGS2022

Rotenone induces mortality of invasive Lake Trout and Rainbow Trout embryos

Objective Nonnative fish, including Lake Trout Salvelinus namaycush and Rainbow Trout Oncorhynchus mykiss , are actively invading lakes and streams and threatening Cutthroat Trout O. clarkii and other native species in the western United States. Programs have been implemented to suppress invasive trout using netting, trapping, electrofishing, angling, or other traditional capture methods. Because these methods are costly and primarily target older, free-swimming life stages, development of new suppression methods that target embryos on spawning areas is desired to increase suppression efficacy and reduce long-term costs. Methods We evaluated the capability of rotenone, N -methylpyrrolidone, diethylene glycol ethyl ether, sodium chloride, calcium carbonate, and gelatin to induce mortality of Lake Trout and Rainbow Trout embryos in controlled laboratory experiments. Result Exposure to liquid and powdered rotenone formulations for 12 h at 4 mg/L caused 98% ± 0.7 (mean ± SE) and 99% ± 0.6 Lake Trout mortality, respectively. Exposure to liquid and powdered rotenone formulations for 12 h at 4 mg/L caused 62% ± 4.7 and 85% ± 3.2 Rainbow Trout mortality, respectively. N -methylpyrrolidone, diethylene glycol ethyl ether, sodium chloride, calcium carbonate, and gelatin exposures were not effective at increasing embryo mortality of either species. Conclusion Developing embryos represent a vulnerable life history stage that can be exploited by targeted applications of rotenone. Incorporating novel suppression techniques that effectively increase mortality of embryos in an integrated pest management approach may enhance effective suppression of invasive fishes.

Transactions of the American Fisheries Society↗

USGS2022

A scaled Denil fishway for upstream passage of Arctic Grayling

Denil fishways have been used with varying success to help fish pass impediments to upstream passage such as low head dams or irrigation diversion structures. They have been tested for hydraulic and fish passage performance in laboratory and field settings, usually with only minor modifications to the fishway geometry or dimensions. We tested a reduced (0.6) scale prototype of the standard-sized Denil fishway to determine if the smaller fishway, which requires less water flow, would successfully pass Arctic Grayling ( Thymallus arcticus ). The scaling factor was informed by analyzing previously published scalable Denil fishway rating equations. A prototype was tested in an open-channel flume using 8 treatments with 3 trials per treatment and 8 fish per trial. Each treatment had a prescribed combination of headwater and tailwater depths. Overall, 93% (178/191) of the fish volitionally entered the fishway and of these 91% (162/178) passed successfully. Entrance and passage were reduced only in treatments with the highest hydraulic slopes and highest water velocities at the downstream end of the fishway (i.e. with high headwater depths and low tailwater depths). The 0.6-scaled Denil fishway is likely a good alternative to standard-sized Denil fishways to enhance upstream mobility of Arctic Grayling in small, water-limited streams.

Journal of Ecohydraulics↗

USGS2022

The importance of phenology and thermal exposure to early life history success of nonnative Smallmouth Bass in the Yellowstone River

Knowledge of potential spread by introduced species is critical to effective management and conservation. The Smallmouth Bass Micropterus dolomieu is an example of a fish that has been introduced globally, often spreads after introduction, and has substantial predatory impacts on fish assemblages. Nonnative Smallmouth Bass in the free-flowing Yellowstone River, Montana, have expanded from warmer, downstream sections of river into colder, upstream sections containing socio-economically valuable trout fisheries. We sought insight into mechanisms controlling upstream spread by evaluating whether progressively colder upstream climates physiologically constrained successful recruitment by limiting age-0 growth and preventing overwinter survival (i.e., population establishment). We documented the phenology, growth, and overwinter survival of age-0 Smallmouth Bass across a temperature gradient leading to their upstream extent in the Yellowstone River. The upstream extent of population establishment did not appear limited by water temperature alone. Age-0 body size at the onset of winter did not differ significantly between colder, upstream reaches and warmer, downstream reaches. Instead, the earlier hatch timing exhibited by some age-0 individuals in upstream sections allowed them to experience longer growing seasons than many individuals in downstream sections. This counter-intuitive hatching phenology mediated much of the expected decreases in growth in colder, upstream climates. Furthermore, evidence of successful overwinter survival and simulations of age-0 starvation mortality indicated that age-0 individuals at the upstream extent of their distribution successfully recruited to the age-1 year-class during four consecutive years. However, age-0 individuals were rare or absent throughout the uppermost upstream distribution of adults, suggesting that something other than temperature limits or discourages reproduction farther upstream. Taken together, our results suggest that Smallmouth Bass have not yet reached the thermal limit of their upstream distribution in the Yellowstone River and that future spread may challenge fisheries managers tasked with management of coldwater trout fisheries in this river.

Montana, Wyoming↗

USGS2022

Attraction, entrance, and passage efficiency of Arctic Grayling, trout, and suckers at Denil fishways in the Big Hole River basin, Montana

The Big Hole River basin in southwestern Montana supports the only indigenous, self‐sustaining fluvial population of Arctic Grayling Thymallus arcticus in the conterminous United States, but the basin is fragmented by numerous low‐head irrigation diversion dams. Denil fishways at 63 diversion dams provide Arctic Grayling and other fishes opportunities for year‐round access to critical habitats; however, their efficiency has not been evaluated. We quantified attraction, entrance, and passage for hatchery‐reared Arctic Grayling, wild trout (Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta ), and wild suckers (White Sucker Catostomus commersonii and Longnose Sucker C. catostomus ) during 14 field trials conducted at six Denil fishways over a representative range of fishway slopes and hydraulic conditions using passive integrated transponder telemetry. Attraction (60.4–84.3%) and entrance (44.3–78.6%) efficiencies were variable across test conditions and reduced overall fishway efficiencies (19.1–55.8%). In contrast, upon entry, passage efficiencies were high (96.2–97.0%) for all taxa across all test conditions. Attraction of hatchery‐reared Arctic Grayling increased with upstream depth (a surrogate for fishway discharge) and attraction flow, but attraction of wild fish was less affected by these conditions. Entrance of Arctic Grayling, Brook Trout, and Brown Trout decreased with upstream depth and fishway slope, especially when plunging entrance conditions associated with shallow downstream depths were present. However, entrance of Arctic Grayling and both trout species increased with downstream depth, and submerged fishway entrances demonstrated promise for increasing entrance efficiency at fishways with high discharges and steep slopes. We demonstrate that comprehensive evaluations of fishway efficiency components can identify specific solutions that improve fishway efficiency; application of these engineering solutions at individual fishways (as needed) could improve their efficiency and further enhance aquatic connectivity for fishes in the Big Hole River basin and elsewhere.

Montana↗

USGS2021

Evaluation of remote site incubators to incubate wild- and hatchery-origin Westslope Cutthroat Trout embryos

Fish managers must weigh trade-offs among cost, speed, efficiency, and ecological adaptation when deciding how to translocate native salmonids to either establish or genetically augment populations. Remote site incubators (RSIs) appear to be a reasonable strategy, but large-scale evaluations of this method have been limited. We used 129 RSIs to incubate >35,700 eyed embryos of Westslope Cutthroat Trout Oncorhynchus clarkii lewisi at eight sites within the upper 30 km of the Cherry Creek basin (Madison River, Montana) from 2007 to 2010, after using piscicides to remove all fish. We obtained gametes from 258 parental-pair crosses (164 females and 258 males) from four wild populations and two hatchery broods. All embryos were incubated to the eyed stage in two hatcheries prior to placing them in RSIs. Green-to-eyed egg survivals were higher for progeny of wild-spawned adults (median, 91.0%; 95% CI, 88.7–93.7%) than for progeny of hatchery-spawned adults (median, 81.7%; 95% CI, 74.9–88.4%), and this difference was highly significant ( P < 0.01). Over 26,500 fry were counted leaving RSIs. Median embryo-to-fry survival was 75.6% (95% CI, 72.2–79.0%). Fry exited individual RSIs from 8 to 45 d after embryo translocation. Fry survivals differed among years and sites, and year was more important than site in explaining variation in survival. The success of RSI fry introductions was confirmed by annual monitoring of fish abundance, which indicated that abundances of Westslope Cutthroat Trout 5 to 9 years after RSI introductions were equal to or higher than abundances of nonnative salmonids prior to their removal using piscicides.

Montana↗

USGS2021

It’s complicated…environmental DNA as a predictor of trout and char abundance in streams

The potential to provide inferences about fish abundance from environmental (e)DNA samples has generated great interest. However, the accuracy of these abundance estimates is often low and variable across species and space. A plausible refinement is the use of common aquatic habitat monitoring data to account for attributes that influence eDNA dynamics. We therefore evaluated the relationships between eDNA concentration and abundance of bull trout ( Salvelinus confluentus ), westslope cutthroat trout ( Oncorhynchus clarkii lewisi ) and rainbow trout ( Oncorhynchus mykiss ) at 42 stream sites in the Intermountain West (USA and Canada) and tested whether accounting for site-specific habitat attributes improved the accuracy of fish abundance estimates. eDNA concentrations were positively associated with fish abundance, but these relationships varied by species and site, and there was still considerable variation unaccounted for. Random site-level differences explained much of this variation, but specific habitat attributes of those sites explained relatively small amounts of this variation. Our results underscore that either eDNA sampling or environmental characterization will require further refinement before eDNA can be used reliably to estimate fish abundance in streams.

Idaho, Montana, Oregon, Washington↗

USGS2021

Movements of selected minnows between the lower Yellowstone River and its tributaries

Reduced population connectivity has been implicated as a cause of decreased distributions and abundances of many Great Plains fishes. However, scant empirical evidence quantifying movement and relating the contribution of spatial linkages to population abundances and resilience exists. We used otolith microchemistry analysis to characterize the movements of western silvery minnows ( Hybognathus argyritis Girard, 1856), flathead chubs ( Platygobio gracilis (Richardson, 1836)), and sand shiners ( Notropis stramineus (Cope, 1865)) between the Yellowstone River and its tributaries. Sixty-nine percent of western silvery minnows, 65% of flathead chubs, and 42% of sand shiners moved between the Yellowstone River and tributaries. Mean total number of interchanges was highest among western silvery minnows (4.8 interchanges/mover), intermediate among flathead chubs (4.3 interchanges/mover), and lowest among sand shiners (1.4 interchanges/mover; P < 0.01). Natal movements were rare, but juvenile movements were common and frequent among all three species. Movements between main-stem and tributary habitats are probably prominent facets of the life cycles of other Great Plains minnows. Therefore, connectivity among such habitats should be a high conservation priority to enhance the long-term viability of such fishes.

Great Plains, Yellowstone River↗

USGS2020

Groundwater upwelling regulates thermal hydrodynamics and salmonid movements during high-temperature events at a montane tributary confluence

The Smith River is a popular recreational sport fishery in western Montana, but salmonid abundances there are thought to be artificially limited by riparian land-use alterations, irrigation water withdrawals, and high summer water temperatures. We used integrated networks of temperature loggers, PIT tag antenna stations, and in situ temperature mapping to investigate the thermal hydrodynamics and associated movements of PIT-tagged salmonids at the confluence of Tenderfoot Creek, a major, unaltered coldwater tributary of the Smith River. Contrary to expectations, Tenderfoot Creek itself was not used as a thermal refuge by salmonids during periods of high water temperatures in Smith River; rather, its cool outflow plume into the main stem was used instead. Mean daily outflow water temperatures averaged 2.9°C lower than those of the Smith River during summer and ranged from 0.5°C to 6.1°C lower. Moreover, measured and estimated temperatures in the outflow were cooler (by up to 2.8°C) than in Tenderfoot Creek itself at times as a result of groundwater upwelling at the confluence. Detections of PIT-tagged fish in the thermal plume increased, especially at night, when daily mean water temperatures exceeded 20°C in the main-stem Smith River; more than four times as many PIT-tagged fish were detected in the plume ( N = 52) than along the opposite bank ( N = 12), which ostensibly afforded better cover. Coldwater tributary confluences may provide superior thermal refuges for salmonids—cooler than the tributaries themselves—when water temperatures in river main stems are stressful.

Montana↗

USGS2020

Benthic suffocation of invasive lake trout embryos by fish carcasses and sedimentation in Yellowstone Lake

Introduced Lake Trout Salvelinus namaycush threaten native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in Yellowstone Lake, Yellowstone National Park, where gill nets have been used to suppress subadult and adult Lake Trout since 1995. However, survival of embryonic and larval life history stages can have profound effects on the population dynamics of Lake Trout. Inducing additional mortality at those stages, especially if used in concert with intensive gillnetting of older fish, could enhance overall suppression efforts. Therefore, we conducted controlled field experiments at Yellowstone Lake to systematically evaluate the effects of sediment deposition and ground Lake Trout carcass deposition on Lake Trout embryos in pre-positioned incubators. Sediment deposition caused dissolved oxygen concentrations to decline below lethal levels for a prolonged overwinter period (92 d). Embryo mortality among overwintering incubators varied from 97.0 ± 5.3% (mean ± SE) at the substrate surface to 100.0 ± 0.0% at 20 cm below the substrate surface. Decomposition of ground carcass material on spawning sites caused dissolved oxygen concentrations to decline to lethal levels (<3.4 mg/L) for about 9 d after biomass application rates of 14 and 28 kg/m 2 in treatment plots. Exposure to ground carcass material resulted in 100.0 ± 0.0% embryo mortality at the substrate surface and within interstices 20 cm below the surface in 14- and 28-kg/m 2 biomass treatments. Embryo mortality was probably caused by hypoxic conditions within substrates in both experiments. The deposition of sediment and ground Lake Trout carcass material on Lake Trout spawning sites in Yellowstone Lake could provide an additional source of mortality in ongoing Lake Trout suppression efforts. These methods may also be beneficial in other systems when incorporated in an integrated pest management approach targeting multiple life history stages of invasive freshwater fish.

Wyoming↗

USGS2020

Yellowstone Lake ecosystem restoration: A case study for invasive fish management

Invasive predatory lake trout Salvelinus namaycush were discovered in Yellowstone Lake in 1994 and caused a precipitous decrease in abundance of native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri. Suppression efforts (primarily gillnetting) initiated in 1995 did not curtail lake trout population growth or lakewide expansion. An adaptive management strategy was developed in 2010 that specified desired conditions indicative of ecosystem recovery. Population modeling was used to estimate effects of suppression efforts on the lake trout and establish effort benchmarks to achieve negative population growth (λ < 1). Partnerships enhanced funding support, and a scientific review panel provided guidance to increase suppression gillnetting effort to >46,800 100-m net nights; this effort level was achieved in 2012 and led to a reduction in lake trout biomass. Total lake trout biomass declined from 432,017 kg in 2012 to 196,675 kg in 2019, primarily because of a 79% reduction in adults. Total abundance declined from 925,208 in 2012 to 673,983 in 2019 but was highly variable because of recruitment of age-2 fish. Overall, 3.35 million lake trout were killed by suppression efforts from 1995 to 2019. Cutthroat trout abundance remained below target levels, but relative condition increased, large individuals (> 400 mm) became more abundant, and individual weights doubled, probably because of reduced density. Continued actions to suppress lake trout will facilitate further recovery of the cutthroat trout population and integrity of the Yellowstone Lake ecosystem.

Wyoming↗

USGS2020

Two Ocean Pass: An alternative hypothesis for invasion of Yellowstone Lake by lake trout, and implications for future invasions

Preventing the interbasin transfer of aquatic invasive species is a high priority for natural resource managers. Such transfers can be made by humans or can occur by dispersal through connected waterways. A natural surface water connection between the Atlantic and Pacific drainages in North America exists at Two Ocean Pass south of Yellowstone National Park. Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri used this route to cross the Continental Divide and colonize the Yellowstone River from ancestral sources in the Snake River following glacial recession 14,000 bp. Nonnative lake trout Salvelinus namaycush were stocked into lakes in the Snake River headwaters in 1890 and quickly dispersed downstream. Lake trout were discovered in Yellowstone Lake in 1994 and were assumed to have been illegally introduced. Recently, lake trout have demonstrated their ability to move widely through river systems and invade headwater lakes in Glacier National Park. Our objective was to determine if lake trout and other nonnative fish were present in the connected waters near Two Ocean Pass and could thereby colonize the Yellowstone River basin in the past or future. We used environmental DNA (eDNA), electrofishing, and angling to survey for lake trout and other fishes. Yellowstone cutthroat trout were detected at nearly all sites on both sides of the Continental Divide. Lake trout and invasive brook trout S. fontinalis were detected in Pacific Creek near its confluence with the Snake River. We conclude that invasive movements by lake trout from the Snake River over Two Ocean Pass may have resulted in their colonization of Yellowstone Lake. Moreover, Yellowstone Lake may be vulnerable to additional invasions because several other nonnative fish inhabit the upper Snake River. In the future, eDNA collected across smaller spatial intervals in Pacific Creek during flow conditions more conducive to lake trout movement may provide further insight into the extent of non-native fish invasions in this stream.

Idaho, Montana, Wyoming↗

USGS2019

Organic pellet decomposition induces mortality of Lake Trout embryos in Yellowstone Lake

Yellowstone Lake is the site of actions to suppress invasive Lake Trout Salvelinus namaycush and restore native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri and natural ecosystem function. Although gill netting is effective (Lake Trout λ ≤ 0.6 from 2012 through 2018), the effort costs more than US$2 million annually and only targets Lake Trout age 2 and older. To increase suppression efficiency, we developed an alternative method using organic (soy and wheat) pellets to increase mortality of Lake Trout embryos on spawning sites. Decomposition of pellets during two in situ experiments caused dissolved oxygen (DO) concentrations to temporarily decline to lethal levels (<3.4 mg/L) within days of application. Embryo mortalities during the first exposure period (days 1–6 following application) were high at all treatment levels (1.75–28.0 kg/m 2 ) at the substrate surface and within interstices 20 cm below the surface, varying from 97 ± 1.8% (mean ± SE) to 100 ± 0.0%, but may have been enhanced by a handling effect (exposure to sunlight). Embryo mortalities during the second exposure period (days 11–22) were highest 20 cm below the surface, varying from 78 ± 9.7% to 100 ± 0.0%. Almost all (98 ± 3.1%) Lake Trout embryos died after exposure to DO < 3.4 mg/L for >200 h during the second period. Pellets caused lethal DO for several weeks below the substrate surface, despite largely dissolving and dissipating from the surface of treated areas by day 39. Broad-scale application of pellets at 1.75 kg/m 2 following the spawning period in autumn may reduce Lake Trout recruitment and enhance population suppression because the area of 14 verified spawning sites is only 11.4 ha (0.03% of lake surface area). Pellet application may be useful in other similar systems as part of an integrated pest management approach targeting multiple life stages of invasive freshwater fish.

Wyoming↗

USGS2019

Riverine turtles select habitats maintained by natural discharge regimes in an unimpounded large river

Turtle populations are imperiled worldwide, but limited ecological information from unaltered systems hampers science‐based management and conservation of some species, especially riverine turtles such as the spiny softshell ( Apalone spinifera ). We therefore investigated movements and spatial habitat selection of 54 A . spinifera in 633 river kilometres (rkm) of the least‐altered river in the conterminous United States—the Yellowstone River in Montana—from 2005 to 2009. Movement rates and home ranges were smaller than in fragmented, altered river systems because nesting and overwintering habitats were common and in close proximity. Habitat selection also differed. A . spinifera in the Yellowstone River overwintered in unaltered bluff pools and summered in complex reaches with side channels, islands, and diverse habitats. However, those in the highly altered Missouri River used deep alluvial pools for overwintering and flooded, inundated, or backwatered tributary mouths in spring and summer. Importantly, selected habitats in both rivers were functionally similar, including complex river reaches (with multiple channels, islands, and diverse habitats) and natural pool types. Unfortunately, these are the very habitats that are limited in rivers affected by dams, bank stabilization, and channelization. Therefore, preservation of natural and diverse riverine habitats—and the fluvial dynamics that maintain them—may enhance conservation of A . spinifera in large rivers.

Montana, North Dakota, South Dakota, Wyoming↗

USGS2019

In situ evaluation of benthic suffocation methods for suppression of invasive Lake Trout embryos in Yellowstone Lake

Suppression of invasive Lake Trout Salvelinus namaycush is an important management tool to use in native fish and ecosystem conservation throughout the U.S. Intermountain West. Lake Trout suppression, primarily by gill netting, has been ongoing in Yellowstone Lake, Yellowstone National Park, Wyoming, since 1995. Additional methods that cause mortality of Lake Trout embryos could be used simultaneously with gill netting to enhance suppression. Our objective was to evaluate the in-situ efficacy of two benthic suffocation methods—tarping with gas-impermeable tarps and Lake Trout carcass deposition to increase the mortality of Lake Trout embryos. Tarping did not increase embryo mortality; mean control mortality was 21 ± 1.9% (mean ± SE), and mean tarp-treatment mortality was 20 ± 2.9%. Lake Trout carcass deposition caused 98 ± 1.2% mean mortality of embryos at the substrate surface and 100 ± 0.1% mean mortality of embryos 20 cm below the substrate surface. Hypoxic conditions in the carcass treatments were probably the cause of the high embryo mortality; dissolved oxygen concentrations at the substrate surface declined from 7.74 to 0.06 mg/L when carcasses remained on the treatment locations. The deposition of Lake Trout carcasses shows potential to be an additional suppression method that can induce mortality in Lake Trout embryos through benthic suffocation and could be implemented at Lake Trout spawning sites in Yellowstone Lake.

Wyoming↗