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At least 667 records · Page 37Linked to original sources

USGS2016

Benefits of prescribed flows for salmon smolt survival enhancement vary longitudinally in a highly managed river system

The influence of streamflow on survival of emigrating juvenile Pacific salmonids Oncorhynchus spp. (smolts) is a major concern for water managers throughout the northeast Pacific Rim. However, few studies have quantified flow effects on smolt survival, and available information does not indicate a consistent flow–survival relationship within the typical range of flows under management control. In the Yakima Basin, Washington, the potential effects of streamflow alterations on smolt survival have been debated for over 20 years. Using a series of controlled flow releases from upper basin reservoirs and radiotelemetry, we quantified the relationship between flow and yearling Chinook salmon smolt survival in the 208 km reach between Roza Dam and the Yakima River mouth. A multistate mark–recapture model accounted for weekly variation in flow conditions experienced by tagged fish in four discrete river segments. Smolt survival was significantly associated with streamflow in the Roza Reach [river kilometre (rkm) 208–189] and marginally associated with streamflow in the Sunnyside Reach (rkm 169–77). However, smolt survival was not significantly associated with flow in the Naches and Prosser Reaches (rkm 189–169 and rkm 77–3). This discrepancy indicates potential differences in underlying flow-related survival mechanisms, such as predation or passage impediments. Our results clarify trade-offs between flow augmentation for fisheries enhancement and other beneficial uses, and our study design provides a framework for resolving uncertainties about streamflow effects on migratory fish survival in other river systems.

Washington↗

USGS2020

Assessing the potential for spectrally based remote sensing of salmon spawning locations

Remote sensing tools are increasingly used for quantitative mapping of fluvial habitats, yet few techniques exist for continuous sampling of aquatic organisms, such as spawning salmonids. This study assessed the potential for spectrally based remote sensing of salmon spawning locations (i.e., redds) using data acquired from unmanned aircraft systems (UAS) along a large, gravel‐bed river. We developed a novel, semi‐automated approach for detecting salmon redds by applying machine learning classification and object detection techniques to UAS‐based imagery. We found that both true colour (RGB) and hyperspectral imagery could be used to identify salmon redds, though with varying degrees of accuracy. Redds were mapped with accuracies of ~0.75 from RGB imagery using logistic regression and support vector machines (SVM) classification algorithms, but this type of data could not be used to identify redds using Object‐based Image Analysis (OBIA). The hyperspectral imagery was more useful for mapping salmon redds, with accuracies greater than 0.9 for both logistic regression and SVM classifiers; OBIA of the hyperspectral data resulted in redd detection accuracies up to 0.86. The hyperspectral imagery also yielded complementary physical habitat information including water depth and substrate composition, which we quantified on the basis of a spectrally based chlorophyll absorption ratio. Overall, the hyperspectral imagery more effectively identified salmon spawning locations than RGB images and was more conducive to the classification approaches we evaluated. Each type of remotely sensed data had advantages and limitations, which are important for potential users to understand when incorporating UAS‐based data collection into river ecosystem studies.

California↗

USGS2018

Fall and winter microhabitat use and suitability for spring chinook salmon parr in a U.S. Pacific Northwest River

Habitat degradation has been implicated as a primary threat to Pacific salmon Oncorhynchus spp. Habitat restoration and conservation are key toward stemming population declines; however, winter microhabitat use and suitability knowledge are lacking for small juvenile salmonids. Our objective was to characterize microhabitat use and suitability for spring Chinook Salmon Oncorhynchus tshawytscha parr during fall and winter. Using radiotelemetry techniques during October–February (2009–2011), we identified fall and winter microhabitat use by spring Chinook Salmon parr in Catherine Creek, northeastern Oregon. Tagged fish occupied two distinct gradient reaches (moderate and low). Using a mixed‐effects logistic regression resource selection function (RSF) model, we found evidence that microhabitat use was similar between free‐flowing and surface ice conditions. However, habitat use shifted between seasons; most notably, there was greater use of silt substrate and areas farther from the bank during winter. Between gradients, microhabitat use differed with greater use of large wood (LW) and submerged aquatic vegetation in the low‐gradient reach. Using a Bayesian RSF approach, we developed gradient‐specific habitat suitability criteria. Throughout the study area, deep depths and slow currents were most suitable, with the exception of the low‐gradient reach where moderate depths were optimal. Near‐cover coarse and fine substrates were most suitable in the moderate‐ and low‐gradient reaches, respectively. Near‐bank LW was most suitable throughout the study area. Multivariate principal component analyses (PCA) indicated co‐occurring deep depths supporting slow currents near cover were intensively occupied in the moderate‐gradient reach. In the low‐gradient reach, PCA indicated co‐occurring moderate depths, slow currents, and near‐bank cover were most frequently occupied. Our study identified suitable and interrelated microhabitat combinations that can guide habitat restoration for fall migrant and overwintering Chinook Salmon parr in Catherine Creek and potentially the Pacific Northwest.

Oregon↗

USGS2018

Juvenile Chinook Salmon mortality in a Snake River Reservoir: Smallmouth Bass predation revisited

Predation by nonnative fishes has been identified as a contributing factor in the decline of juvenile salmonids in the Columbia River basin. We examined the diet composition of Smallmouth Bass Micropterus dolomieu and estimated the consumption and predation loss of juvenile Chinook Salmon Oncorhynchus tshawytscha in Lower Granite Reservoir on the Snake River. We examined 4,852 Smallmouth Bass stomachs collected from shoreline habitats during April–September 2013–2015. Chinook Salmon were the second most commonly consumed fish by all size‐classes of Smallmouth Bass (≥150 mm TL) throughout the study. Over the 3 years studied, we estimated that a total of 300,373 Chinook Salmon were consumed by Smallmouth Bass in our 22‐km study area, of which 97% (291,884) were subyearlings (age 0) based on length frequency data. A majority of the loss (61%) occurred during June, which coincided with the timing of hatchery releases of subyearling fall Chinook Salmon. Compared to an earlier study, mean annual predation loss increased more than 15‐fold from 2,670 Chinook Salmon during 1996–1997 to 41,145 Chinook Salmon during 2013–2015 (in reaches that could be compared), despite lower contemporary Smallmouth Bass abundances. This increase can be explained in part by increases in Smallmouth Bass consumption rates, which paralleled increases in subyearling Chinook Salmon densities—an expected functional response by an opportunistic consumer. Smallmouth Bass are currently significant predators of subyearling Chinook Salmon in Lower Granite Reservoir and could potentially be a large source of unexplained mortality.

Idaho, Washington↗

USGS2018

Effects of climate-related stream factors on patterns of individual summer growth of Cutthroat Trout

Coldwater fishes are sensitive to abiotic and biotic stream factors, which can be influenced by climate. Distributions of inland salmonids in North America have declined significantly, with many of the current strongholds located in small headwater systems that may serve as important refugia as climate change progresses. We investigated the effects of discharge, stream temperature, trout biomass, and food availability on summer growth of Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri , a species of concern with significant ecological value. Individual size, stream discharge, sample section biomass, and temperature were all associated with growth, but had differing effects on energy allocation. Stream discharge had a positive relationship with growth rates in length and mass; greater rates of prey delivery at higher discharges probably enabled trout to accumulate reserve tissues in addition to structural growth. Temperature effects were positive but not significant, and support in growth models was limited, likely due to the cold thermal regimes of the study area. The strength of the discharge effect on growth suggests that climate adaptation strategies for coldwater fishes that focus solely on thermal characteristics may be misleading and highlights the importance of considering multiple factors, including hydrologic regimes, in conservation planning.

Montana, Wyoming↗

USGS2019

Using the Distinct Population Segment concept to protect fishes with low levels of genomic differentiation: conservation of an endemic minnow (Hitch, Lavinia exilicauda)

In the United States, the Endangered Species Act (ESA) of 1973 was enacted to conserve species which are endangered or threatened throughout all or a portion of their range. The definition of ‘species’ includes subspecies and distinct population segments (DPSs). In freshwater fishes, use of DPS designations has largely been restricted to salmonid fishes (Salmonidae), although the DPS concept is increasingly applied to other fishes as well. As more taxa approach threatened status, the difficult question becomes what to do when genetic evidence does not strongly support formal taxonomic designations (full species or subspecies). We examine the potential use of the DPS concept to protect fishes using the example of Hitch ( Lavinia exilicauda ), a cyprinid fish endemic to California. The Hitch is divided up into three formally described, geographically separated subspecies. However, genomic studies (RADseq), presented here with three independent analyses using a large data set, only weakly support subspecies designations. Results suggest population but not subspecies structure. Nevertheless, conventional taxonomic methods, strong contemporary isolation, the importance of protecting genetic diversity, and high cultural values still qualify all three designated subspecies for DPS status and demonstrate how taxa such as Clear Lake Hitch can warrant protection under the ESA.

Transactions of the American Fisheries Society↗

USGS2019

New insights into the ecology of adfluvial Bull Trout and the population response to the Endangered Species Act in the North Fork Lewis River, Washington

Like many other salmonids, Bull Trout Salvelinus confluentus migratory life-history expressions are becoming increasingly rare. A critical step in effectively refining management and conservation strategies is a robust assessment of the effectiveness of such strategies and key biological information used in monitoring and recovery planning. To address this need, we integrated a variety of methods to evaluate the population demographics (abundance), vital rates (survival), and life-history characteristics (ageing, growth, spawning migrations and iteroparity) of an adfluvial Bull Trout population. We also employed our mark-recapture data to quantify if recruitment or adult survival had a greater contribution to population trends from year to year. Our results indicated Bull Trout spawning migrations vary with body size, as a considerable portion of smaller adults (<650 mm) did not spawn each year. Additionally, most spawning individuals made only one spawning migration, while <13% made three or more spawning migrations. Our abundance and survival data, which extends to the early 1990s, illustrated positive responses in survival and abundance following the protection of Bull Trout under the Endangered Species Act (1998). Over this period, we found high interannual variability in both survival and abundance, and adult survival (average = 0.45, SE = 0.04) was surprisingly lower than subadult individuals (average = 0.66, SE = 0.04), suggesting limitations at this important life stage. Our mark-recapture data also suggested the attributes driving the Bull Trout population trend (i.e., recruitment to the adult stage or adult survival) has varied through time, with declining trends in the relative contribution of recruitment. Our results provide new insights into the life-history patterns of adfluvial Bull Trout and can serve as a template to consider factors potentially limiting this and other native trout populations.

Washington↗

USGS2019

Effects of multiple nonnative fish on an imperiled cyprinid, Hornyhead Chub

Nonnative fish can have substantial negative effects on the abundance and distribution of native fishes through predation and competition. Nonnative predators are of particular interest because they represent novel threats to native prey species that are not adapted to their presence. Prey species with limited distributions or population sizes may be particularly vulnerable to the effects of nonnative predators. In the Laramie River, four nonnative predators—Brown Trout Salmo trutta , Rainbow Trout Oncorhynchus mykiss , Brook Trout Salvelinus fontinalis, and Smallmouth Bass Micropterus dolomieu are present along with a state‐imperiled population of Hornyhead Chub Nocomis biguttatus . The abundance of Hornyhead Chub has declined with increasing abundance of nonnative predators, with the probability of occurrence of Hornyhead Chub dropping drastically when Smallmouth Bass were present. All four nonnative species preyed on native cyprinids, but Smallmouth Bass relied most heavily on fish as a prey item. Isotopic niche overlap occurred between Hornyhead Chub and all of the nonnative predator species. Our results demonstrate that nonnative predators have the potential to negatively affect the abundance and distribution of Hornyhead Chub through the mechanisms of predation and competition, and predator identity is important in determining the extent of effects. Smallmouth Bass are a greater concern than nonnative salmonids because of their more piscivorous behavior, and their recent upstream expansion may be limiting the downstream distribution of Hornyhead Chub in the Laramie River.

Wyoming↗

USGS2021

Juvenile Coho and Chinook salmon growth, size, and condition linked to watershed-scale salmon spawner abundance

Anadromous Pacific salmon Oncorhynchus spp. are semelparous, and resource subsidies from spawning adult salmon (marine-derived nutrients [MDN]) benefit juvenile salmonids while they rear in freshwater. However, it is unclear if juvenile salmon populations respond predictably to the abundance of spawning salmon at the watershed scale. To address whether hypothesized benefits to rearing juveniles scale up to population and watershed scales, we examined juvenile Coho Salmon Oncorhynchus kisutch and Chinook Salmon O. tshawytscha growth, fork length, condition, and abundance as a function of MDN assimilation throughout the Unalakleet and North rivers in western Alaska. Additionally, a mark–recapture experiment provided abundance estimates of Coho Salmon smolts emigrating from these two rivers. Prior to spawning, residual MDN from past years offered little advantage to juvenile salmon. However, after the arrival of spawning adults, juveniles demonstrated a positive relationship between MDN and fish size, growth, and condition in fall and winter. Out-migrating smolts also benefitted from MDN resources via increased size and growth rates. Coho Salmon smolt abundance was unrelated to total spawner biomass, but a positive relationship between MDN assimilation and smolt abundance suggested a possible effect on overwinter survival. Furthermore, similar trends in spawner biomass and the abundance of age-1 smolts suggested that age at smolting was influenced by MDN. These relationships support the hypothesis that salmon spawner abundance during Coho and Chinook Salmon rearing is an important factor in the juvenile productivity of these species.

Alaska↗

USGS2022

Food web perspectives and methods for riverine fish conservation

Food web analyses offer useful insights into understanding how species interactions, trophic relationships, and energy flow underpin important demographic parameters of fish populations such as survival, growth, and reproduction. However, the vast amount of food web literature and the diversity of approaches can be a deterrent to fisheries practitioners engaged in on-the-ground research, monitoring, or restoration. Incorporation of food web perspectives into contemporary fisheries management and conservation is especially rare in riverine systems, where approaches often focus more on the influence of physical habitat and water temperature on fish populations. In this review, we first discuss the importance of food webs in the context of several common fisheries management issues, including assessing carrying capacity, evaluating the effects of habitat change, examining species introductions or extinctions, considering bioaccumulation of toxins, and predicting the effects of climate change and other anthropogenic stressors on riverine fishes. We then examine several relevant perspectives: basic food web description, metabolic models, trophic basis of production, mass-abundance network approaches, ecological stoichiometry, and mathematical modeling. Finally, we highlight several existing and emerging methodologies including diet and prey surveys, eDNA, stable isotopes, fatty acids, and community and network analysis. Although our emphasis and most examples are focused on salmonids in riverine environments, the concepts are easily generalizable to other freshwater fish taxa and ecosystems.

Wiley Interdisciplinary Reviews (WIREs): Water↗

USGS2013

Black bear density in Glacier National Park, Montana

We report the first abundance and density estimates for American black bears ( Ursus americanus ) in Glacier National Park (NP),Montana, USA.We used data from 2 independent and concurrent noninvasive genetic sampling methods—hair traps and bear rubs—collected during 2004 to generate individual black bear encounter histories for use in closed population mark–recapture models. We improved the precision of our abundance estimate by using noninvasive genetic detection events to develop individual-level covariates of sampling effort within the full and one-half mean maximum distance moved (MMDM) from each bear’s estimated activity center to explain capture probability heterogeneity and inform our estimate of the effective sampling area.Models including the one-halfMMDMcovariate received overwhelming Akaike’s Information Criterion support suggesting that buffering our study area by this distance would be more appropriate than no buffer or the full MMDM buffer for estimating the effectively sampled area and thereby density. Our modelaveraged super-population abundance estimate was 603 (95% CI¼522–684) black bears for Glacier NP. Our black bear density estimate (11.4 bears/100 km2, 95% CI¼9.9–13.0) was consistent with published estimates for populations that are sympatric with grizzly bears (U. arctos) and without access to spawning salmonids. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

Montana↗

USGS2015

Developing nondestructive techniques for managing conflicts between fisheries and double-crested cormorant colonies

Double-crested cormorants ( Phalacrocorax auritus ) have been identified as the source of significant mortality to juvenile salmonids ( Oncorhynchus spp.) in the Columbia River Basin. Management plans for reducing the size of a large colony on East Sand Island (OR, USA) in the Columbia River estuary are currently being developed. We evaluated habitat enhancement and social attraction as nondestructive techniques for managing cormorant nesting colonies during 2004–2007. We tested these techniques on unoccupied plots adjacent to the East Sand Island cormorant colony. Cormorants quickly colonized these plots and successfully raised young. Cormorants also were attracted to nest and raised young on similar plots at 2 islands approximately 25 km from East Sand Island; 1 island had a history of successful cormorant nesting whereas the other was a site where cormorants had previously nested unsuccessfully. On a third island with no history of cormorant nesting or nesting attempts, these techniques were unsuccessful at attracting cormorants to nest. Our results suggest that some important factors influencing attraction of nesting cormorants using these techniques include history of cormorant nesting, disturbance, and presence of breeding cormorants nearby. These techniques may be effective in redistributing nesting cormorants away from areas where fish stocks of conservation concern are susceptible to predation, especially if sites with a recent history of cormorant nesting are available within their foraging or dispersal range. Published 2015. Wiley Periodicals, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.

Oregon, Washington↗

USGS2000

The presence of high-affinity, low-capacity estradiol-17β binding in rainbow trout scale indicates a possible endocrine route for the regulation of scale resorption

High-affinity, low-capacity estradiol-17β (E 2 ) binding is present in rainbow trout scale. The K d and B max of the scale E 2 binding are similar to those of the liver E 2 receptor ( K d is 1.6 ± 0.1 and 1.4 ± 0.1 nM, and B max is 9.1 ± 1.2 and 23.1 ± 2.2 fmol × mg protein -1 , for scale and liver, respectively), but different from those of the high-affinity, low-capacity E 2 binding in plasma ( K d is 4.0 ± 0.4 nM and B max is 625.4 ± 63.1 fmol × mg protein −1 ). The E 2 binding in scale was displaced by testosterone, but not by diethylstilbestrol. Hence, the ligand binding specificity is different from that of the previously characterized liver E 2 receptor, where E 2 is displaced by diethylstilbestrol, but not by testosterone. The putative scale E 2 receptor thus appears to bind both E 2 and testosterone, and it is proposed that the increased scale resorption observed during sexual maturation in both sexes of several salmonid species may be mediated by this receptor. No high-affinity, low-capacity E 2 binding could be detected in rainbow trout gill or skin.

General and Comparative Endocrinology↗

USGS1994

Vulnerability to predation and physiological stress responses of experimentally descaled juvenile Chinook salmon, Oncorhynchus tshawytscha

Juvenile salmonids, Oncorhynchus spp., commonly encounter conditions (e.g., during hatchery release and dam passage) that result in damage to the skin, scale, and slime complex. We conducted laboratory experiments to determine if descaling of juvenile chinook salmon, O. tshawytscha , increased their vulnerability to predation, and to assess the physiological stress responses elicited by descaling. Salmon were experimentally descaled on either 10% or 20% of their total body area. When offered equal numbers of control and descaled juvenile chinook salmon, northern squawfish, Ptychocheilus oregonensis , did not consume significantly more of either prey type (48–60% of consumed prey were descaled). Juvenile chinook salmon descaled on 10% of their body area did show significant physiological stress responses, however. Mean concentrations of plasma cortisol peaked 1 h after descaling, and returned to control levels by 12 h. Plasma glucose peaked 3 h post-treatment and remained elevated for 24 h. Plasma lactate increased immediately following treatment and returned to undisturbed control levels by 3 h. The osmoregulatory response of plasma potassium was highly variable, but plasma sodium decreased immediately and remained low for 24 h. The observed physiological responses suggest that descaling of juvenile chinook salmon could result in decreased resistance to disease and other stressors encountered in the field, possibly leading to reduced performance capacity and lowered survival.

Environmental Biology of Fishes↗

USGS2011

Chronic toxicity of erythromycin thiocyanate to Daphnia magna in a flow-through, continuous exposure test system

Approval of a new animal drug application for AQUAMYCIN 100 ® (erythromycin thiocyanate; ET) to treat freshwater salmonid species with bacterial kidney disease is being pursued in the US. As part of the approval process, ET’s impact on an aquatic environment had to be described in an environmental assessment. The environmental assessment was lacking data to characterize the effect ET would have on a chronically exposed aquatic invertebrate organism. A major step to fulfilling the environmental assessment was completed after conducting a comprehensive study continuously exposing Daphnia magna to ET for 21 days. Results indicated that the no observable effect concentration for ET was 179 μg/L.

Bulletin of Environmental Contamination and Toxico↗

USGS2025

Energetic value of Arctic forage-sized fish with implications for a nearshore seabird predator

Arctic cod ( Boreogadus saida , also called polar cod) are considered the single most important Arctic forage fish due to their high abundance and nutritional quality. Because Arctic cod are strongly ice associated and prefer colder waters, their frequency in coastal waters has declined with warming, decreasing availability to nearshore predators. To consider the nutritional quality of alternative prey, we measured energy density and estimated whole-body energy of forage-size (39–200 mm) fishes collected during summers 2021–2023 ( n = 274). The fishes sampled included 16 potential prey species from Foggy Island Bay (70.3°N, 147.5°W, near Prudhoe Bay) and Lion Bay (70.2°N, 146.4°W, near Flaxman Island), northern Alaska. Dry weight energy densities ranged from 16.2 to 27.5 kJ g -1 (mean ± SD = 22.0 ± 1.73 kJ g -1 , n = 274) across individuals. Of common species, Arctic cod had the highest mean energy density (24.3 ± 1.1 kJ g -1 , n = 25) and fourhorn sculpin ( Myoxocephalus quadricornis ) had the lowest (19.7 ± 0.8 kJ g -1 , n = 20). To account for size differences among prey species, whole-body energy of typical fish sizes available to predators were modeled using whole-body energy to length relationships and length distributions. Juvenile salmonids (e.g., ciscoes and whitefishes) provided the most energy per individual and were four-fold greater than smaller-bodied Arctic cod. Predators that consume juvenile ciscoes and whitefishes may be more resilient to declines in Arctic cod availability than predators with smaller gapes.

Alaska↗

USGS2009

An ecological risk assessment of the exposure and effects of 2,4-D acid to rainbow trout ( Oncorhyncus mykiss )

Numerous state and federal agencies are increasingly concerned with the rapid expansion of invasive, noxious weeds across the United States. Herbicides are frequently applied as weed control measures in forest and rangeland ecosystems that frequently overlap with critical habitats of threatened and endangered fish species. However, there is little published chronic toxicity data for herbicides and fish that can be used to assess ecological risk of herbicides in aquatic environments. We conducted 96-h flowthrough acute and 30-day chronic toxicity studies with swim-up larvae and juvenile rainbow trout ( Onchorhyncus mykiss ) exposed to the free acid form of 2,4-D. Juvenile rainbow trout were acutely sensitive to 2,4-D acid equivalent at 494 mg/L (95% confidence interval [CI] 334–668 mg/L; 96-h ALC 50 ). Accelerated life-testing procedures, used to estimate chronic mortality from acute data, predicted that a 30-day exposure of juvenile rainbow trout to 2,4-D would result in 1% and 10% mortality at 260 and 343 mg/L, respectively. Swim-up larvae were chronically more sensitive than juveniles using growth as the measurement end point. The 30-day lowest observable effect concentration (LOEC) of 2,4-D on growth of swim-up larvae was 108 mg/L, whereas the 30-day no observable effect concentration (NOEC) was 54 mg/L. The 30-day maximum acceptable toxicant concentration (MATC) of 2,4-D for rainbow trout, determined as the geometric mean of the NOEC and the LOEC, was 76 mg/L. The acute:chronic ratio was 6.5 (i.e., 494/76). We observed no chronic effects on growth of juvenile rainbow trout at the highest concentration tested (108 mg/L). Worst-case aquatic exposures to 2,4-D (4 mg/L) occur when the herbicide is directly applied to aquatic ecosystems for aquatic weed control and resulted in a 30-day safety factor of 19 based on the MATC for growth (i.e., 76/4). Highest nontarget aquatic exposures to 2,4-D applied following terrestrial use is calculated at 0.136 mg/L and resulted in a 30-day safety factor of 559 (e.g., 76/0.163). Assessment of the exposure and response data presented herein indicates that use of 2,4-D acid for invasive weed control in aquatic and terrestrial habitats poses no substantial risk to growth or survival of rainbow trout or other salmonids, including the threatened bull trout ( Salvelinus confluentus ).

Archives of Environmental Contamination and Toxico↗

USGS2012

Mercury and selenium concentrations in biofilm, macroinvertebrates, and fish collected in the Yankee Fork of the Salmon River, Idaho, USA, and their potential effects on fish health

The Yankee Fork is a large tributary of the Salmon River located in central Idaho, USA, with an extensive history of placer and dredge-mining activities. Concentrations of selenium (Se) and mercury (Hg) in various aquatic trophic levels were measured in the Yankee Fork during 2001 and 2002. Various measurements of fish health were also performed. Sites included four on the mainstem of the Yankee Fork and two off-channel sites in partially reclaimed dredge pools used as rearing habitat for cultured salmonid eggs and fry. Hg concentrations in whole mountain whitefish and shorthead sculpin ranged from 0.28 to 0.56 μg/g dry weight (dw), concentrations that are generally less than those reported to have significant impacts on fish. Biofilm and invertebrates ranged from 0.05 to 0.43 μg Hg/g dw. Se concentrations measured in biota samples from the Yankee Fork were greater than many representative samples collected in the Snake and Columbia watersheds and often exceeded literature-based toxic thresholds. Biofilm and invertebrates ranged from 0.58 to 4.66 μg Se/g dw. Whole fish ranged from 3.92 to 7.10 μg Se/g dw, and gonads ranged from 6.91 to 31.84 μg Se/g dw. Whole-body Se concentrations exceeded reported toxicological thresholds at three of four sites and concentrations in liver samples were mostly greater than concentrations shown to have negative impacts on fish health. Histological examinations performed during this study noted liver abnormalities, especially in shorthead sculpin, a bottom-dwelling species.

Idaho↗