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USGS2019

Does vegetation change over 28 years affect habitat use and reproductive success?

Individuals should prefer and use habitats that confer high fitness, but habitat use is not always adaptive. Vegetation in natural landscapes changes gradually and the ability of species to adaptively adjust their habitat use to long-term changes is largely unstudied. We studied nest patch and territory use over 28 yr in Orange-crowned Warblers ( Oreothlypis celata ) in a system that has undergone natural long-term changes in vegetation. Abundance of maple ( Acer grandidentatum ), its preferred nesting habitat, gradually declined from 1987 to 2015. We examined whether habitat use and its fitness consequences changed as the availability of preferred habitat decreased. We used resource selection function models to determine changes over time in the probability of using a nest patch given available patches, and the probability of using a territory given available territories. We estimated nest survival to evaluate changes over time in the fitness consequences of nest patch use. We also compared habitat use (nest patch and territory) and fitness (nest survival) between areas with naturally reduced abundance of maple and experimentally increased abundance of maple (fenced areas). Nest patch use depended on maple abundance and did not change drastically across 28 yr, even though the availability of preferred maple patches decreased over time. In contrast, nest survival tended to decrease over time. We did not see differences in nest patch use and nest survival between unfenced and fenced areas, unlike territory use, which increased with the abundance of maple in fenced areas and decreased in unfenced areas. Our study depicts one example of relatively unchanged habitat use in the face of decreased availability of preferred vegetation across years, with a resulting decrease in reproductive success. Investigating changes in habitat use and fitness consequences for animals exposed to long-term habitat change is necessary to understand adaptive behavioral responses.

Arizona↗

USGS2020

Felsic melt and gas mobilisation during magma solidification: An experimental study at 1.1 kbar

Melt and gas transfer processes are essential to the formation and growth of the Earth’s crust and for sustaining volcanic activity. These processes also play a major role in magma fractionation at shallow depths (<10 km) where magmas stall rheologically and solidify. In this scenario, the conditions of melt and gas mobilization during progressive cooling of crystal mushes down to their solidus remain poorly understood. We present experimental data (at 1.1 kbar) showing how a combination of temperature and crystal content control the ability of melt and gas to escape from cooling and solidifying hydrous silicic magmas with initial crystal volume fractions (Φ) of 0.6, 0.7, and 0.8, and for temperature snapshots of 850, 800, and 750°. Microstructural observations and chemical data show that the amount of extracted melt increases by 70% from 850 to 750° and by 40% from Φ = 0.6 to 0.8 at 750°, due to the formation of interconnected crystal frameworks, gas expansion in constricted pore space, and filter pressing during cooling. As a result, our experiments suggest that melt and gas extraction from cooling mushes increases in proximity to their solidus and can operate efficiently at 0.6 < Φ <0.93. These observations shed light on maximum estimates of the segregation of gas-rich, crystal-poor magmas (0.02 m/year at 850° to 9 m/year at 750°) to form felsic dykes or eruptible systems feeding volcanoes.

Frontiers in Earth Science↗

USGS2024

Defining sediment handling practices to limit negative impacts to larval lampreys

Sediment manipulation activities such as dredging and restoration efforts (e.g., culvert install/repair) may disturb habitats where larval lampreys live burrowed in stream sediments. Sediment added on top of larval lamprey burrowing areas results in ‘overburden’, which poses risks of mortality from respiratory distress, reduced movement, and crushing injuries or may have sublethal effects such as changes in growth or burrowing activity. To avoid negative outcomes, larvae must be able to vertically migrate through the overburden to reach areas near the new (elevated) sediment-water interface. Current guidance on how to limit negative impacts to lampreys during sediment handling activities is limited by a lack of information on how lampreys respond to overburden. The goal of this study was to evaluate larval lamprey responses to variable overburden depths and exposure durations using two sediment types: fine (<0.250 mm) and sand (0.250 - 0.500 mm). We assessed lamprey (mix of Pacific Lamprey Entosphenus tridentatus and Lampetra spp.) survival and injury and evaluated burrowing performance as an indicator of sublethal impacts of overburden stress. We designed an experimental system using 15-cm diameter plastic tubes partitioned into sections that allowed us to describe the approximate vertical position of larval lampreys within the overburden so we could assess vertical migration ability. The tube sections were stacked in a column and secured using straps. The bottom tube section was 10 cm tall and was attached to a flat, rectangular base plate. This section was filled with sediment and lampreys at the start of a test. The middle tube sections were each 10 cm tall, with the number of sections adapted to the depth of the overburden. The top tube section was 20 cm tall to allow room for 10 cm of water over the surface of the overburden. Sampling involved removing the tubes from a holding tank and quickly separating the sections to locate lampreys and assign their position to the tube section where they were recovered. Our primary objectives for the study were to better understand how depth of overburden and exposure duration affect larval lampreys, but there was no previously published information to inform our selection of test parameters. Thus, we used a two phased approach where Phase 1 was a pre-test to help us refine appropriate treatments for Phase 2. In Phase 1 of the study, we used a constant overburden depth (50 cm) and exposure duration (24 h) to compare four sediment treatments that varied the initial burrowing sediment and the overburden sediment: fine-fine, fine-sand, sand-fine, sand-sand. In all four treatments, most lampreys vertically migrated through the overburden and were recovered in the uppermost tube section 24 h after overburden was added. There were no lamprey mortalities, few injuries, and little evidence of sublethal effects of overburden stress based on burrowing performance tests. Lampreys moved the most in the fine-sand and fine-fine treatments, so they were used for continued testing. In Phase 2 we doubled the overburden depth to 100 cm and tested extended exposure durations (1 to 4 d), and based on those results, added tests of shorter durations (1 to 8 h). Since both treatments used fine sediment for initial borrowing, these tests effectively compared fine and sand sediments as overburden. Overall for Phase 2, there were no lamprey mortalities, little evidence of sublethal effects, and 6.4% of the treatment fish were injured. Most of the injuries were mild abrasions, but some fish had serious damage such as a large gash or nearly complete bisection. We estimate that the serious injuries occurred as tube sections were separated during sampling, but the cause of the minor injuries could not be clearly ascribed to overburden stress or sampling activity. Lampreys moved to the upper sections of the tubes through 100 cm of fine and sand overburden within 1 d. Lamprey position was comparable among the 1-4 d exposures, although position was more variable at 1 d compared to 4 d. Tests of exposures less than 24 h showed that fewer than 40% of lampreys completed vertical migrations to the top of the tube after 4 h, and after 8 h the uppermost tube section contained 33% of lampreys in the sand treatment and 44% of lampreys in the fine treatment. We concluded that the minimum time needed for most lampreys to complete vertical migrations through 100 cm of overburden lies somewhere between 8 and 24 h. Lamprey size influenced recovery position in 4 and 8 h exposures to sand overburden, but not for other tests. The mean size of fish near the bottom of the tubes was significantly larger than the size of fish near the top of the tubes. To our knowledge this was the first formal study to evaluate lamprey responses to overburden. Although our test systems were imperfect simulations of natural conditions, and several questions would benefit from additional research, our findings can inform guidelines on sediment handling practices to limit negative impacts to larval lampreys.

Report↗

USGS2018

Consequences of abrading bed load on vertical and lateral bedrock erosion in a curved experimental channel

In this study, we conducted multiple physical experiments to estimate the efficacy and spatial pattern of erosion by abrading sediment moving through a simple U‐shaped channel bend with erodible bed and banks. The experiments showed that in the bend, lateral abrasion followed a monotonically increasing linear relationship with sediment feed rate. However, vertical incision had a more complex relation with the sediment feed rate, with an initial increase in abrasion as the feed rate increased followed by a decrease in abrasion of the bed as cover effects became dominant at higher feed rates. Bank erosion was large in places where the width and the lateral slope of the point bar were relatively large. On the other hand, in places where the width of the point bar was smaller, the bedrock bed was eroded primarily along the boundary of the point bar, resulting in a bedrock bench near the outer bank.

Shimanto River↗

USGS1994

Electrochemistry and dissolution kinetics of magnetite and ilmenite

Natural samples of magnetite and ilmenite were experimentally weathered in pH 1–7 anoxic solutions at temperatures of 2–65 °C. Reaction of magnetite is described as [ Fe 2+ Fe 2 3+ ] O 4(magnetite) + 2 H + → γ [ Fe 2 3+ ] O 3(maghemite) + Fe 2+ + H 2 O . Dynamic polarization experiments using magnetite electrodes confirmed that this reaction is controlled by two electrochemical half cells, 3[ Fe 2+ Fe 2 3+ ] O 4 (magnetite) → 4 γ [ Fe 2 3+ ] O 3 (maghemite) + Fe 2+ + 2 e − and [ Fe 2+ Fe 2 3+ ] O 4(magnetite) + 8 H + + 2 e − → 3 Fe 2+ + 4 H 2 O , which result in solid state Fe 3+ reduction, formation of an oxidized layer and release of Fe(II) to solution. XPS data revealed that iron is present in the ferric state in the surfaces of reacted magnetite and ilmenite and that the Ti Fe "> TiFe ratio increased with reaction pH for ilmenite. Short-term (<36 h) release rates of Fe(II) were linear with time. Between pH 1 and 7, rates varied between 0.3 and 13 × 10 −14 mol · cm −2 · s −1 for magnetite and 0.05 and 12.3 × 10 −14 mol · cm −2 · s −1 for ilmenite. These rates are two orders of magnitude slower than electrochemical rates determined by Tafel and polarization resistance measurements. Discrepancies are due to both differences in geometric and BET surface area estimates and in the oxidation state of the mineral surface. In long-term closed-system experiments (<120 days), Fe(II) release slowed with time due to the passivation of the surfaces by increasing thicknesses of oxide surface layers. A shrinking core model, coupling surface reaction and diffusion transport, predicted that at neutral pH, the mean residence time for sand-size grains of magnetite and ilmenite will exceed 10 7 years. This agrees with long-term stability of these oxides in the geologic record.

Geochimica et Cosmochimica Acta↗

USGS2017

Rates of soil development from four soil chronosequences in the southern Great Basin

Four soil chronosequences in the southern Great Basin were examined in order to study and quantify soil development during the Quaternary. Soils of all four areas are developed in gravelly alluvial fans in semiarid climates with 8 to 40 cm mean annual precipitation. Lithologies of alluvium are granite-gneiss at Silver Lake, granite and basalt at Cima Volcanic Field, limestone at Kyle Canyon, and siliceous volcanic rocks at Fortymile Wash. Ages of the soils are approximated from several radiometric and experimental techniques, and rates are assessed using a conservative mathematical approach. Average rates for Holocene soils at Silver Lake are about 10 times higher than for Pleistocene soils at Kyle Canyon and Fortymile Wash, based on limited age control. Holocene soils in all four areas appear to develop at similar rates, and Pleistocene soils at Kyle Canyon and Fortymile Wash may differ by only a factor of 2 to 4. Over time spans of several millennia, a preferred model for the age curves is not linear but may be exponential or parabolic, in which rates decrease with increasing age. These preliminary results imply that the geographical variation in rates within the southern Great Basin-Mojave region may be much less significant than temporal variation in rates of soil development. The reasons for temporal variation in rates and processes of soil development are complexly linked to climatic change and related changes in water and dust, erosional history, and internally driven chemical and physical processes. ?? 1991.

Quaternary Research↗

USGS1993

Evaluating landsat thematic mapper derived vegetation indices for estimating above-ground biomass on semiarid rangelands

Ground data from the Central Plains Experimental Range in northeast Colorado and Landsat satellite images of that area acquired in August 1989, June 1990, and September 1990 were used to evaluate the level of association that can be expected from a univariate model relating spectrally derived vegetation indices (difference, ratio, and normalized difference vegetation indices) and dried green vegetation biomass. The vegetation indices were related to the ground sample estimates using a sample point, spectral class, and greenness strata approach. No strong relationships were found between the vegetation indices and sample estimates of dried green biomass using the sample point approach. The spectral class approach produced significant results only for the June 1990 sample period ( r =0.96). Significant relationships were found for the August 1989, June 1990, and September 1990 samples periods ( r 2 =0.95, 0.71, and 0.95, respectively) when the data were aggregated by greenness strata. The high degree of association between green biomass and the NDVI, obtained when the data were combined into greenness strata, indicated that it is possible to predict green biomass levels on semiarid rangelands using univariate regression models.

Remote Sensing of Environment↗

USGS2021

Relating Tmax and hydrogen index to vitrinite and solid bitumen reflectance in hydrous pyrolysis residues: Comparisons to natural thermal indices

Vitrinite reflectance (VR o ; %) generally is considered the most reliable technique to determine the thermal maturity of sedimentary rocks. However, it is a time-consuming process to collect reflectance (R o ; %) measurements and is subjective to the interpretation of each trained technician, who must be able to discern between vitrinite and solid bitumen and other organic matter types. Inadvertent misidentification of solid bitumen for vitrinite can lead to reports of ‘suppressed’ VR o , especially at lower thermal maturities (< 1.0% R o ). Programmed pyrolysis data, such as T max and hydrogen index (HI), are comparatively inexpensive and more time-efficient to obtain than R o data and are determined by instrument settings, rather than by operator decision, and are therefore independent of operator-based training or experience bias. This study uses hydrous pyrolysis (HP) residues from various coals and shales to relate measured VR o and solid bitumen reflectance (BR o ; %) values to their respective T max and HI values and determines whether these relationships can be used as a proxy to calculate R o in naturally matured samples. Although the estimation of R o is not always accurate, the results demonstrate that relational equations for shales and coals derived from the T max and HI data of HP residues can effectively calculate R o in natural series. Approximately 60% of calculated R o from T max and 83% of calculated R o from HI relational equations are within interlaboratory reproducibility limits (± 0.2% shale BR o ; ± 0.06% coal VR o ) when compared to their respective measured R o values from natural series. Variables that may affect accuracy of the applied relational equations include variable sedimentary organic matter composition of samples, differences of maturation reaction kinetics of the sedimentary organic matter in experimental versus natural settings, and decreasing reliability of all thermal proxy measurements at higher maturities.

International Journal of Coal Geology↗

USGS2012

Arsenic-induced biochemical and genotoxic effects and distribution in tissues of Sprague-Dawley rats

Arsenic (As) is a well documented human carcinogen. However, its mechanisms of toxic action and carcinogenic potential in animals have not been conclusive. In this research, we investigated the biochemical and genotoxic effects of As and studied its distribution in selected tissues of Sprague–Dawley rats. Four groups of six male rats, each weighing approximately 60 ± 2 g, were injected intraperitoneally, once a day for 5 days with doses of 5, 10, 15, 20 mg/kg BW of arsenic trioxide. A control group was also made of 6 animals injected with distilled water. Following anaesthetization, blood was collected and enzyme analysis was performed by spectrophotometry following standard protocols. At the end of experimentation, the animals were sacrificed, and the lung, liver, brain and kidney were collected 24 h after the fifth day treatment. Chromosome and micronuclei preparation was obtained from bone marrow cells. Arsenic exposure significantly increased ( p < 0.05) the activities of plasma alanine aminotransferase–glutamate pyruvate transaminase (ALT/GPT), and aspartate aminotransferase–glutamate oxaloacetate transaminase (AST/GOT), as well as the number of structural chromosomal aberrations (SCA) and frequency of micronuclei (MN) in the bone marrow cells. In contrast, the mitotic index in these cells was significantly reduced ( p < 0.05). These findings indicate that aminotransferases are candidate biomarkers for arsenic-induced hepatotoxicity. Our results also demonstrate that As has a strong genotoxic potential, as measured by the bone marrow SCA and MN tests in Sprague–Dawley rats. Total arsenic concentrations in tissues were measured by inductively coupled plasma mass spectrometry (ICP-MS). A dynamic reaction cell (DRC) with hydrogen gas was used to eliminate the ArCl interference at mass 75, in the measurement of total As. Total As doses in tissues tended to correlate with specific exposure levels.

Microchemical Journal↗

USGS2020

Category count models for adaptive management of metapopulations: Case study of an imperiled salamander

Managing spatially structured populations of imperiled species presents many challenges. Spatial structure can make it difficult to predict population responses to potential recovery activities, and learning through experimentation may not be advised if it could harm threatened populations. Adaptive management provides an appealing framework when experimentation is considered too risky or time consuming; we used such an approach for imperiled flatwoods salamanders at a Florida wildlife refuge. We represented this metapopulation with category count models and used stochastic dynamic programming to identify optimal decision policies that weighed trade‐offs between metapopulation persistence and management costs. We defined possible wetland categories in terms of habitat suitability and occupancy, specified category‐specific management actions, and identified transition probabilities via expert elicitation for two management strategies: “future” status quo (FSQ; frequent growing‐season burns) and extra management actions (EMA; restoration, translocation, head‐starting). We simulated metapopulation dynamics using the resulting optimal management policy and found that under model FSQ, occupancy steadily declined over time, indicating that populations would rapidly become extirpated; with model EMA, occupancy remained stable, suggesting that populations would persist only if additional actions are applied and are effective. This approach can be used to identify optimal solutions while accounting for uncertainty and considering both habitat and population dynamics, and to help managers make conservation decisions for populations at imminent risk of extinction.

Florida↗

USGS2018

Rearing performance of juvenile brown trout Salmo trutta fed a bioprocessed soybean meal diet with differing velocity regimes

This 121-day experiment evaluated the rearing performance of brown trout Salmo trutta fed one of two isonitrogenous and isocaloric diets (46% protein, 16% lipid) and reared at velocities of either 2.8 or 16.1 cm/s. Fishmeal was the primary protein source for the reference diet, which was compared to a bioprocessed soybean meal ingredient that replaced approximately 67% of the fishmeal in the experimental diet. At the end of the experiment, there were no significant differences in gain, percent gain, feed conversion rates, nor specific growth rates between the dietary treatments. There were also no significant differences in intestinal morphology, splenosomatic, hepatosomatic, and viscerosomatic indices related to diet composition. However, gain, percent gain, feed fed, and specific growth rate were all significantly greater in brown trout reared at the higher velocity. No significant differences in any of the other variables measured were observed between the velocity treatments. There were no significant interactions between diet and velocity in any of the variables. Based on the results of this study, bioprocessed soybean meal can replace at least 67% of the fish meal in brown trout diets, regardless of the rearing velocities used in this study. Higher rearing velocities are recommended to maximize juvenile brown trout growth rates.

Open Journal of Animal Sciences↗

USGS1979

Monitoring massive fracture growth at 2-km depths using surface tiltmeter arrays

Tilt due to massive hydraulic fractures induced in sedimentary rocks at depths of up to 2.2 km have been recorded by surface tiltmeters. Injection of fluid volumes up to 4 · 10 5 liters and masses of propping agent up to 5 · 10 5 kg is designed to produce fractures approximately 1 km long, 50–100 m high and about 1 cm wide. The surface tilt data adequately fit a dislocation model of a tensional fault in a half-space. Theoretical and observational results indicate that maximum tilt occurs at a distance off the strike of the fracture equivalent to 0.4 of the depth to the fracture. Azimuth and extent of the fracture deduced from the geometry of the tilt field agree with other kinds of geophysical measurements. Detailed correlation of the tilt signatures with pumping parameters (pressure, rate, volume, mass) have provided details on asymmetry in geometry and growth rate. Whereas amplitude variations in tilt vary inversely with the square of the depth, changes in flow rate or pressure gradient can produce a cubic change in width. These studies offer a large-scale experimental approach to the study of problems involving fracturing, mass transport, and dilatancy processes.

Tectonophysics↗

USGS2015

Climate change and physical disturbance cause similar community shifts in biological soil crusts

Biological soil crusts (biocrusts)—communities of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface—are fundamental components of drylands worldwide, and destruction of biocrusts dramatically alters biogeochemical processes, hydrology, surface energy balance, and vegetation cover. While there has been long-standing concern over impacts of 5 physical disturbances on biocrusts (e.g., trampling by livestock, damage from vehicles), there is also increasing concern over the potential for climate change to alter biocrust community structure. Using long-term data from the Colorado Plateau, USA, we examined the effects of 10 years of experimental warming and altered precipitation (in full-factorial design) on biocrust communities, and compared the effects of altered climate with those of long-term physical 10 disturbance (>10 years of replicated human trampling). Surprisingly, altered climate and physical disturbance treatments had similar effects on biocrust community structure. Warming, altered precipitation frequency [an increase of small (1.2 mm) summer rainfall events], and physical disturbance from trampling all promoted early successional community states marked by dramatic declines in moss cover and increased cyanobacteria cover, with more variable effects 15 on lichens. While the pace of community change varied significantly among treatments, our results suggest that multiple aspects of climate change will affect biocrusts to the same degree as physical disturbance. This is particularly disconcerting in the context of warming, as temperatures for drylands are projected to increase beyond those imposed by the climate treatments used in our study.

PNAS↗

USGS2014

Structure and vulnerability of Pacific Northwest tidal wetlands – A summary of wetland climate change research by the Western Ecology Division, U.S. EPA

Climate change poses a serious threat to the tidal wetlands of the Pacific Northwest (PNW) region of the U.S. In response to this threat, scientists at the Western Ecology Division of the U.S. EPA at and the Western Fisheries Research Center of the U.S. Geological Survey, along with other partners, initiated a series of studies on the structure and vulnerability of tidal wetlands to climate change. One research thrust was to evaluate community structure of PNW marshes, experimentally assess the vulnerability of marsh plants to inundation and salinity stress (as would happen with sea level rise), and evaluate the utility of the National Wetland Inventory (NWI) classification system. Another research thrust was to develop tools that provide insights into possible impacts of climate change. This effort included enhancing the Sea Level Affecting Marshes Model (SLAMM) to predict the effects of sea level rise on submerged aquatic vegetation (Zostera marina) distributions, evaluating changes in river flow into coastal estuaries in response to precipitation changes, and synthesizing Pacific Coast estuary, watershed, and climate data in a downloadable tool. Because the research resulting from these efforts was published in multiple venues, we summarized them in this document. We anticipate that future research efforts by the U.S. EPA will continue with a focus on climate change impacts on a regional scale.

California, Oregon, Washington↗

USGS2005

Experimental and geochemical evidence for derivation of the El Capitan Granite, California, by partial melting of hydrous gabbroic lower crust

Partial melting of mafic intrusions recently emplaced into the lower crust can produce voluminous silicic magmas with isotopic ratios similar to their mafic sources. Low-temperature (825 and 850°C) partial melts synthesized at 700 MPa in biotite-hornblende gabbros from the central Sierra Nevada batholith (Sisson et al. in Contrib Mineral Petrol 148:635–661, 2005) have major-element and modeled trace-element (REE, Rb, Ba, Sr, Th, U) compositions matching those of the Cretaceous El Capitan Granite, a prominent granite and silicic granodiorite pluton in the central part of the Sierra Nevada batholith (Yosemite, CA, USA) locally mingled with coeval, isotopically similar quartz diorite through gabbro intrusions (Ratajeski et al. in Geol Soc Am Bull 113:1486–1502, 2001). These results are evidence that the El Capitan Granite, and perhaps similar intrusions in the Sierra Nevada batholith with lithospheric-mantle-like isotopic values, were extracted from LILE-enriched, hydrous (hornblende-bearing) gabbroic rocks in the Sierran lower crust. Granitic partial melts derived by this process may also be silicic end members for mixing events leading to large-volume intermediate composition Sierran plutons such as the Cretaceous Lamarck Granodiorite. Voluminous gabbroic residues of partial melting may be lost to the mantle by their conversion to garnet-pyroxene assemblages during batholithic magmatic crustal thickening.

Contributions to Mineralogy and Petrology↗

USGS2009

Attempts to identify Clostridium botulinum toxin in milk from three experimentally intoxicated Holstein cows

Three adult lactating Holstein cows were injected in the subcutaneous abdominal vein with 175 ng/kg of body weight of Clostridium botulinum type C toxin (451 cow median toxic doses) to determine if this botulinum toxin crosses the blood–milk barrier. Whole blood (in sodium heparin) and clotted blood serum samples were taken at 0 min, 10 min, and 3, 6, 9, and 12 h postinoculation. Milk samples were taken at 0 min and at 3, 6, 9 and 12 h postinoculation. All samples were tested for the presence of the toxin using the mouse bioassay and immunostick ELISA test. The immunostick ELISA identified the toxin in whole blood and the mouse bioassay identified the toxin in serum at all times examined in all 3 animals. Toxin was not identified by either detection method in milk samples collected from the 3 animals. From these results, it appears that Clostridium botulinum type C toxin does not cross from the blood to the milk in detectable concentrations.

Journal of Dairy Science↗

USGS2013

Assessing effects of stocked trout on nongame fish assemblages in southern Appalachian Mountain streams

Fisheries managers are faced with the challenge of balancing the management of recreational fisheries with that of conserving native species and preserving ecological integrity. The negative effects that nonnative trout species exert on native trout are well documented and include alteration of competitive interactions, habitat use, and production. However, the effects that nonnative trout may exert on nongame fish assemblages are poorly understood. Our objectives were to quantify the effects of trout stocking on native nongame fish assemblages intensively on one newly stocked river, the North Toe River, North Carolina, and extensively on other southern Appalachian Mountain streams that are annually stocked with trout. In the intensive study, we adopted a before-after, control-impact (BACI) experimental design to detect short-term effects on the nongame fish assemblage and found no significant differences in fish density, species richness, species diversity, or fish microhabitat use associated with trout stocking. We observed differences in fish microhabitat use between years, however, which suggests there is a response to environmental changes, such as the flow regime, which influence available habitat. In the extensive study, we sampled paired stocked and unstocked stream reaches to detect long-term effects from trout stocking; however, we detected no differences in nongame fish density, species richness, species diversity, or population size structure between paired sites. Our results revealed high inherent system variation caused by natural and anthropogenic factors that appear to overwhelm any acute or chronic effect of stocked trout. Furthermore, hatchery-reared trout may be poor competitors in a natural setting and exert a minimal or undetectable impact on native fish assemblages in these streams. These findings provide quantitative results necessary to assist agencies in strategic planning and decision making associated with trout fisheries, stream management, and conservation of native fishes.

Transactions of the American Fisheries Society↗

USGS2023

Characterization of fish assemblages in eleven multi-use reservoirs from North Carolina, USA

Managing impounded river systems is a recurring challenge for aquatic resource professionals because reservoirs serve multiple functions with different ecological and socioeconomic outcomes. However, research on fishes in reservoirs has disproportionally focused on recreationally and economically important species, with less attention directed toward fish assemblages despite the potential for management at the assemblage level. As such, evaluation of relationships between reservoir fish assemblages and biotic and abiotic factors and testing whether assemblage structure is affected by changing environmental conditions may deepen ecological understanding and provide insights for reservoir fisheries management. Our overall objective was to assess these relationships in 11 reservoirs from North Carolina, USA. We sampled fish assemblages in the reservoirs, which spanned five river basins representing a range of habitat conditions, using experimental gillnets and pulsed DC nighttime electrofishing. Multivariate statistical analyses indicated that taxonomic differences in fish assemblage composition among river basins followed a gradient of productivity. The top contributing species to reservoir dissimilarity were bluegill ( Lepomis macrochirus ), gizzard shad ( Dorosoma cepedianum ), black crappie ( Pomoxis nigromaculatus ), and white perch ( Morone americana ). These four species were positively associated with factors that reflect increasing eutrophic conditions in the 11 reservoirs and could, therefore, serve as indicators of reservoir productivity, anthropogenic influence, and fish assemblage structure, in addition to their key role in reservoir fisheries management. Whereas fisheries research has historically focused on assessing fish populations, our results illustrate the ecological and management insights derived from simultaneously collecting assemblage- and population-level data. Research on reservoir fish assemblages in relation to biotic and abiotic conditions may help advance fish ecology and management alike.

North Carolina↗