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At least 1,675 records · Page 93Linked to original sources
USGS2019

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

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

Montana↗
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↗
USGS2014

Offshore pelagic fish community

Lake Ontario’s offshore zone, as defined by Stewart et al. (2013), comprises all waters of the lake where the bottom depth is greater than 15 m excluding those in embayments. When the lake is thermally stratified during June-October, the offshore pelagic zone includes the upper-warm and middle-cool layers of water which serve as important habitat for Alewife and other prey fishes, and for predators like salmon and trout. Early changes in the fish community of the offshore pelagic zone are well documented elsewhere (e.g., Smith 1972; Christie 1973) as are more recent changes (e.g., Owens et al. 2003; Mills et al. 2003). Currently the offshore fish community consists of a mix of native and non-native species. Native species are those that were present prior to European colonization and for the offshore pelagic zone, include predators like Atlantic Salmon and prey fish like Cisco, Emerald Shiner, and Threespine Stickleback. Non-native species are those that were introduced unintentionally like Alewife and Rainbow Smelt, or that were introduced intentionally like Chinook Salmon, Coho Salmon, Rainbow Trout, and Brown Trout. Non-native salmon and trout were introduced originally by fisheries managers to provide fishing opportunities and later to reduce an overabundance of Alewife. Alewife is the most abundant prey fish in the offshore pelagic zone and it dominates the diets of native and introduced predators (Brandt 1986; Lantry 2001). Alewife can have direct and indirect negative effects on other fishes through competition for food and/or predation on their larvae (Madenjian et al. 2008). Alewife also contain thiaminase, an enzyme that catalyzes the breakdown of thiamine, and fish that eat mainly Alewife can become thiamine deficient which impairs their reproduction (Honeyfield et al. 2005). Except for that of the Alewife, prey fish populations in the offshore pelagic zone are depressed, and not large enough to sustain the zone’s predators. Alewife remain necessary for a functional ecosystem that is required to sustain a highly-valued, trophy sport fishery (Stewart et al. 2013). Wild production of trout and salmon occurs in Lake Ontario tributaries, contributing to in-lake populations (Rand et al. 1993; Connerton et al. 2009; Connerton et al. 2014c). Stocking hatchery-reared fish (Fig. 1), however, remains an essential tool for managing Lake Ontario’s diverse trout and salmon fisheries and achieving the Offshore Pelagic Zone Goal (Stewart et al. 2013): Maintain the offshore pelagic fish community, that is characterized by a diversity of trout and salmon species including Chinook Salmon, Coho Salmon, Rainbow Trout, Brown Trout, and Atlantic Salmon, in balance with prey-fish populations and lower trophic levels. Here we review the fish-community objectives (FCOs) for Lake Ontario’s offshore pelagic zone (Stewart et al. 2013) and evaluate whether those objectives were met during this reporting period (2008-2013) by assessing the status of the objectives’ indicators. We also compare the status of indicators in this reporting period with those in the previous reporting period (2003-2007) (Connerton et al. 2014b). Specific objectives are in italics at the start of each major section and associated indicators of progress are given in Progress and Outlook subsections.

Lake Ontario↗
USGS2025

Non-native prey availability and over-compensatory density dependence drive population dynamics of a native fish predator

Understanding the factors that regulate population dynamics is crucial for conserving imperiled species. Bull trout ( Salvelinus confluentus ), a piscivorous salmonid and one of North America's most threatened cold-water species, has declined significantly due to habitat loss, overfishing, invasive species, and climate change. While recovery efforts have primarily targeted these threats, the role of prey availability in influencing bull trout population dynamics under multiple stressors remains poorly understood. Using a stage-based integrated population model, we quantified the effects of non-native prey availability (kokanee; Oncorhynchus nerka ), angling pressure, climatic variation, and density-dependent processes on bull trout population dynamics in Lake Koocanusa, a transboundary reservoir and river system (United States and Canada), over a 40-year period (1980–2023). Our results show that bull trout populations are regulated by density-dependent processes, including over-compensation in sub-adult recruitment and reduced adult survival at high densities. Increased kokanee biomass and restricted harvest significantly enhanced bull trout survival and abundance, whereas reduced water availability had a limited negative effect on sub-adult production. Model simulations indicate that as kokanee biomass availability increases, the number of bull trout that can be sustainably harvested also increases. In fact, a modest annual fishery (300 individuals) can be sustained, especially under moderate to high kokanee biomass conditions. These results underscore the importance of prey availability, including non-native species, in supporting bull trout populations. Effective management of threatened apex fish predators like bull trout requires addressing the complex interplay between environmental threats, prey dynamics, and density-dependent mechanisms across all life stages.

British Columbia, Montana↗
USGS2018

A comparative evaluation of crowding stress on muscle HSP90 and myostatin expression in salmonids

Stress is a major factor that contributes to poor production and animal welfare concerns in aquaculture. As such, a thorough understanding of mechanisms involved in the stress response is imperative to developing strategies to mitigate the negative side effects of stressors, including the impact of high stocking densities on growth. The purpose of this study was to determine how the muscle growth inhibitor, myostatin , and the stress-responsive gene HSP90 are regulated in response to crowding stress in rainbow trout ( Oncorhynchus mykiss ), cutthroat trout ( Oncorhynchus clarki ), brook trout ( Salvelinus fontinalis ), and Atlantic salmon ( Salmo salar ). All species exhibited higher cortisol and glucose levels following the handling stress, indicating physiological response to the treatment. Additionally, all species, except rainbow trout, exhibited higher HSP90 levels in muscle after a 48 h crowding stress. Crowding stress resulted in a decrease of myostatin-1a in brook trout white muscle but not red muscle, while, myostatin-1a and -2a levels increased in white muscle and myostatin-1b levels increased in red muscle in Atlantic salmon. In rainbow trout, no significant changes were detected in either muscle type, but myostatin-1a was upregulated in both white and red skeletal muscle in the closely related cutthroat trout. The variation in response to crowding suggests a complex and species-specific interaction between stress and the muscle gene regulation in these salmonids. Only Atlantic salmon and cutthroat trout exhibited increased muscle myostatin transcription, and also exhibited the largest increase in circulating glucose in response to crowding. These results suggest that species-specific farming practices should be carefully examined in order to optimize low stress culture conditions.

Aquaculture↗
USGS2026

Effect of rotenone treatment on alpine stream invertebratecommunities in Colorado

Objective: Introduction of non-native salmonids to western United States streams has resulted in extirpation and even extinction of native cutthroat trout. Once thought to be extinct, a genetically verified population of Greenback Cutthroat Trout (GBCT) Oncorhynchus virginalis stomias was identified and used for population re-establishment efforts. To restore native trout habitat, stream reaches above a dispersal barrier are typically treated with a piscicide (i.e., rotenone) to remove non-native trout before reintroduction of natives. One concern with this method is the possible impact to non-target invertebrates, which are an important food source for trout, and a drastic disturbance to invertebrates following rotenone treatment could negatively affect native trout establishment. Methods: Two alpine streams were treated with liquid rotenone via drip stations during two consecutive days. Invertebrate communities were sampled for six years in two streams where GBCT was reintroduced. Pre- and posttreatment sampling allowed for examination of short-term, intermediate, and long-term responses to invertebrate communities. Results: Negative short-term responses were detected for total taxa richness, EPT richness, and percent Heptageniidae density immediately following rotenone application. However, most community metrics returned to pretreatment values within 1 to 2 years posttreatment. Invertebrate community changes between pretreatment and 3 to 5 years posttreatment were observed with increased percent Chironomidae density and decreased percent EPT (Ephemeroptera, Plecoptera, Trichoptera) density. Conclusion: This study provides insight into invertebrate community response to rotenone treatment in high alpine streams and adds to the current literature which displays short-term declines in invertebrates following rotenone and recovery of most aspects of the initial invertebrate community within one year posttreatment. Lay Summary Rotenone application for cutthroat trout habitat restoration negatively affected invertebrate communities in the 1 to 2 months following treatment; however, most community values recovered to pretreatment levels within 1 to 2 years. Keywords: native fish, cutthroat trout, fish management, invertebrate community, habitat restoration

Colorado↗
USGS2014

Effects of prey abundance, distribution, visual contrast and morphology on selection by a pelagic piscivore

Most predators eat only a subset of possible prey. However, studies evaluating diet selection rarely measure prey availability in a manner that accounts for temporal–spatial overlap with predators, the sensory mechanisms employed to detect prey, and constraints on prey capture. We evaluated the diet selection of cutthroat trout ( Oncorhynchus clarkii ) feeding on a diverse planktivore assemblage in Lake Washington to test the hypothesis that the diet selection of piscivores would reflect random (opportunistic) as opposed to non-random (targeted) feeding, after accounting for predator–prey overlap, visual detection and capture constraints. Diets of cutthroat trout were sampled in autumn 2005, when the abundance of transparent, age-0 longfin smelt ( Spirinchus thaleichthys ) was low, and 2006, when the abundance of smelt was nearly seven times higher. Diet selection was evaluated separately using depth-integrated and depth-specific (accounted for predator–prey overlap) prey abundance. The abundance of different prey was then adjusted for differences in detectability and vulnerability to predation to see whether these factors could explain diet selection. In 2005, cutthroat trout fed non-randomly by selecting against the smaller, transparent age-0 longfin smelt, but for the larger age-1 longfin smelt. After adjusting prey abundance for visual detection and capture, cutthroat trout fed randomly. In 2006, depth-integrated and depth-specific abundance explained the diets of cutthroat trout well, indicating random feeding. Feeding became non-random after adjusting for visual detection and capture. Cutthroat trout selected strongly for age-0 longfin smelt, but against similar sized threespine stickleback ( Gasterosteus aculeatus ) and larger age-1 longfin smelt in 2006. Overlap with juvenile sockeye salmon ( O. nerka ) was minimal in both years, and sockeye salmon were rare in the diets of cutthroat trout. The direction of the shift between random and non-random selection depended on the presence of a weak versus a strong year class of age-0 longfin smelt. These fish were easy to catch, but hard to see. When their density was low, poor detection could explain their rarity in the diet. When their density was high, poor detection was compensated by higher encounter rates with cutthroat trout, sufficient to elicit a targeted feeding response. The nature of the feeding selectivity of a predator can be highly dependent on fluctuations in the abundance and suitability of key prey.

Washington↗
USGS2025

Effects of riparian forest thinning on resident salmonid fishes in coastal northern California catchments

Resource managers are interested in whether thinning second-growth forests may be a viable restoration strategy for stream and riparian habitats, but may be concerned about the potential impacts that increases in stream temperature associated with riparian thinning treatments may have on cold-water salmonid fishes. We evaluated the effects of riparian forest thinning on resident populations of coastal cutthroat trout ( Oncorhynchus clarkii clarkii ) in coastal northern California catchments using a manipulative field experiment with a replicated before-after-control-impact design (pre-treatment data collected in 2016, thinning treatments occurred in 2017, and post-treatment data collected in 2018). Experimental thinning treatments reduced riparian shade by 20%–30% along five 150–200 m stream reaches. To provide a process-based evaluation of the implications of riparian thinning for coastal cutthroat trout, we combined seasonal observations of trout density, biomass, and growth with bioenergetics modelling. Cutthroat trout density increased by 8%–31% and biomass increased by 27%–111% in thinned reaches 1 year post-treatment, but responses varied widely across sites and seasons so did not always differ statistically. Growth rates of cutthroat trout varied more among seasons than among reach types (upstream reference, thinned, and downstream), peaking in spring and overwinter relative to summer. Bioenergetics modelling indicated that cutthroat trout responded to thinning-induced increases in stream temperature and shifts in prey energy density via higher consumption rates (i.e., fish fed more frequently) in thinned reaches. Additionally, reach-scale consumption estimates indicated that the energy intake of cutthroat trout increased at the population level in thinned reaches. However, thinned reaches exhibited relatively small changes in consumption, suggesting that riparian thinning was unlikely to enhance growth opportunities for cutthroat trout, supporting our empirical growth observations. Collectively, our field experiment suggests that salmonid fishes may be resilient to thinning second-growth riparian forests when treatments do not substantially increase water temperatures. Moreover, our results highlight that pairing empirical data with bioenergetics modelling can provide valuable insights into the mechanisms driving fish responses to riparian forest restoration.

California↗
USGS2022

Cohort strength and body size in co-occurring salmonids in a small stream network: Variation in space and time

Trout and salmon commonly coexist in stream networks. Exploring similarities and differences among species can help explain coexistence and invasive ability. Here, we describe spatial distribution, cohort strengths and size-at-age of three co-occurring species in a small stream network. Spatial distributions varied dramatically among species; native brook trout occupied all stream reaches, naturalized brown trout were found in the mainstem and lower portions of tributaries and fry-stocked Atlantic salmon were limited to the mainstem. Size-at-age also differed among species, Atlantic salmon were consistently the smallest, brook trout were intermediate in size and brown trout were the largest. Despite size differences, mean lengths of brook trout and brown trout were highly correlated among years. Cohort strengths varied considerably across years but were also highly correlated for the two trout species, suggesting strong environmental control on cohort strength and a reduced role for species interactions. At low densities, we observed strong negative effects of density on body sizes and weaker effects otherwise. Overall, these results suggest differences in spatial distribution combined with similarities in response to environmental variation contribute to species coexistence in this small steam network.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1994

Why are the PCB concentrations of salmonine individuals from the same lake so highly variable?

An individual-based model (IBM) was applied to the Lake Michigan rainbow trout ( Oncorhynchus mykiss ) population, with the objectives of explaining the observed variation in growth and in polychlorinated biphenyl (PCB) concentration within the population. When variation in prey PCB concentration was incorporated into the model, variability in PCB concentration among individual rainbow trout was fully explained by the IBM. Although number of spawnings and number of years spent in a stream prior to first entering the lake were factors in determining growth, these life history characteristics appeared to have only a minor impact on PCB accumulation rate in rainbow trout. The IBM application to the rainbow trout population was compared with an application to the Lake Michigan lake trout ( Salvelinus namaycush ) population. Modeling results indicated that the lower observed PCB concentrations in rainbow trout compared with lake trout were chiefly due to greater longevity in lake trout. The IBM simulations identified gross growth efficiency, assimilation efficiency of PCBs from food, and diet as other important sources of variability in salmonine PCB concentrations.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2004

Fish assemblage structure and relations with environmental conditions in a Rocky Mountain watershed

Fish and habitat were sampled from 110 reaches in the Salt River basin (Idaho and Wyoming) during 1996 and 1997 to assess patterns in fish assemblage structure across a Rocky Mountain watershed. We identified four distinct fish assemblages using cluster analysis: (1) allopatric cutthroat trout (Oncorhynchus clarki (Richardson, 1836)); (2) cutthroat trout - brook trout (Salvelinus fontinalis (Mitchell, 1814)) - Paiute sculpin (Cottus beldingi Eigenmann and Eigenmann, 1891); (3) cutthroat trout - brown trout (Salmo trutta L., 1758) - mottled sculpin (Cottus bairdi Girard, 1850); and (4) Cyprinidae-Catostomidae. The distribution of fish assemblages was explained by thermal characteristics, stream geomorphology, and local habitat features. Reaches with allopatric cutthroat trout and the cutthroat trout - brook trout - Paiute sculpin assemblage were located in high-elevation, high-gradient streams. The other two fish assemblages were generally located in low-elevation streams. Associations between habitat gradients, locations of reaches in the watershed, and occurrence of species were further examined using canonical correspondence analysis. The results suggest that stream geomorphology, thermal conditions, and local habitat characteristics influence fish assemblage structure across a Rocky Mountain watershed, and they provide information on the ecology of individual species that can guide conservation activities. ?? 2004 NRC Canada.

Canadian Journal of Zoology↗
USGS2017

Beaver colony density trends on the Chequamegon-Nicolet National Forest, 1987 – 2013

The North American beaver ( Castor canadensis ) is a managed species in the United States. In northern Wisconsin, as part of the state-wide beaver management program, the Chequamegon-Nicolet National Forest removes beavers from targeted trout streams on U.S. Forest Service lands. However, the success of this management program has not been evaluated. Targeted removals comprise only 3% of the annual beaver harvest, a level of effort that may not affect the beaver population. We used colony location data along Forest streams from 1987–2013 (Nicolet, northeast Wisconsin) and 1997–2013 (Chequamegon, northwest Wisconsin) to assess trends in beaver colony density on targeted trout streams compared to non-targeted streams. On the Chequamegon, colony density on non-targeted trout and non-trout streams did not change over time, while colony density on targeted trout streams declined and then stabilized. On the Nicolet, beaver colony density decreased on both non-targeted streams and targeted trout streams. However, colony density on targeted trout streams declined faster. The impact of targeted trapping was similar across the two sides of the Forest (60% reduction relative to non-targeted trout streams). Exploratory analyses of weather influences found that very dry conditions and severe winters were associated with transient reductions in beaver colony density on non-targeted streams on both sides of the Forest. Our findings may help land management agencies weigh more finely calibrated beaver control measures against continued large-scale removal programs.

Wisconsin↗
USGS2008

Using bioenergetics modeling to estimate consumption of native juvenile salmonids by nonnative northern pike in the Upper Flathead River System, Montana

Introductions of nonnative northern pike Esox lucius have created recreational fisheries in many waters in the United States and Canada, yet many studies have shown that introduced northern pike may alter the composition and structure of fish communities through predation. We estimated the abundance of nonnative northern pike (2002-2003) and applied food habits data (1999-2003) to estimate their annual consumption of native bull trout Salvelinus confluentus and westslope cutthroat trout Oncorhynchus clarkii lewisi juveniles in the upper Flathead River system, Montana. Population estimates were generally consistent among years and ranged from 1,200 to 1,300 individuals. Westslope cutthroat trout were present in the diet of younger (???600 mm) and older (>600 mm) northern pike during all seasons and bull trout were found only in larger northern pike during all seasons but summer. Bioenergetics modeling estimated that the northern pike population annually consumed a total of 8.0 metric tons (mt) of fish flesh; the highest biomass was composed of cyprinids (4.95 mt) followed by whitefishes Prosopium spp. (1.02 mt), bull trout (0.80 mt), westslope cutthroat trout (0.68 mt), yellow perch Perca flavescens (0.41 mt),1 and other fishes (centrarchids and cottids; 0.14 mt). Numerically, the northern pike population consumed more than 342,000 fish; cyprinids and catostomids comprised approximately 82% of prey fish (278,925), whereas over 13,000 westslope cutthroat trout and nearly 3,500 bull trout were eaten, comprising about 5% of the prey consumed. Our results suggest that predation by introduced northern pike is contributing to the lower abundance of native salmonids in the system and that a possible benefit might accrue to native salmonids by reducing these predatory interactions. ?? Copyright by the American Fisheries Society 2008.

North American Journal of Fisheries Management↗
USGS2015

Fish assemblages in the Upper Esopus Creek, NY: Current status, variability, and controlling factors

The Upper Esopus Creek receives water diversions from a neighboring basin through the Shandaken Tunnel (the portal) from the Schoharie Reservoir. Although the portal is closed during floods, mean flows and turbidity of portal waters are generally greater than in Esopus Creek above their confluence. These conditions could potentially affect local fish assemblages, yet such effects have not been assessed in this highly regulated stream. We studied water quality, hydrology, temperature, and fish assemblages at 18 sites in the Upper Esopus Creek during 2009–2011 to characterize the effects of the portal input on resident-fish assemblages and to document the status of the fishery resource. In general, fish-community richness increased by 2–3 species at mainstem sites near the portal, and median density and biomass of fish communities at sites downstream of the portal were significantly lower than they were at sites upstream of the portal. Median densities of Salmo trutta (Brown Trout) and all trout species were significantly lower than at mainstem sites downstream from the portal—25.1 fish/0.1 ha and 148.9 fish/0.1 ha, respectively—than at mainstem sites upstream from the portal—68.8 fish/0.1 ha and 357.7 fish/0.1 ha, respectively—yet median biomass for Brown Trout and all trout did not differ between sites from both reaches. The median density of young-of-year Brown Trout at downstream sites (9.3 fish/0.1 ha) was significantly lower than at upstream sites (33.9 fish/0.1 ha). Waters from the portal appeared to adversely affect the density and biomass of young-of-year Brown Trout, but lower temperatures and increased flows also improved habitat quality for mature trout at downstream sites during summer. These findings, and those from companion studies, indicate that moderately turbid waters from the portal had few if any adverse impacts on trout populations and overall fish communities in the Upper Esopus Creek during this study.

New York↗
USGS2022

Monitoring fish abundance and behavior, using multi-beam acoustic imaging sonar, at a Selective Water Withdrawal structure in Lake Billy Chinook, Deschutes River, Oregon, 2020

Collection of juvenile salmonids at Round Butte Dam is a critical part of the effort to enhance populations of anadromous fish species in the upper Deschutes River because fish that are not collected at the dam may either incur increased mortality during dam passage or remain landlocked and lost to the anadromous fish population. Adaptive resolution imaging sonar systems were used to assess the behavior, abundance, and timing of fish at the entrance to the Selective Water Withdrawal (SWW) intake and fish collection structure located in the forebay of Round Butte Dam during the spring of 2020. The purpose of the SWW is to direct surface currents in the forebay to attract and collect downriver migrating juvenile salmonid smolts (Chinook salmon [ Oncorhynchus tshawytscha ], sockeye salmon [ O. nerka ], and steelhead [ O. mykiss ]) from Lake Billy Chinook and to enable operators of the SWW to withdraw water from surface and benthic elevations in the reservoir to manage downriver water temperatures. The objective of this study was to assess the abundance and behaviors of smolt-size fish (95–300 millimeters) observed near the SWW and to determine if the presence of bull trout ( Salvelinus confluentus; >350 millimeters), the predominant predator of juvenile salmonids, influenced the behavior of downriver migrants. Two imaging sonar units were deployed during the spring of 2020 smolt out-migration period. One unit monitored fish movements near the entrances and one unit monitored in one of the collection flumes of the SWW. The imaging sonar technology was informative for assessing abundance and spatial and temporal behaviors of smolt and bull trout-size fish. Smolt and bull trout-size fish were regularly observed near the entrance to and in the collection flume. Increased abundances were observed during the night, with corresponding increased discharge through the SWW, compared to during the day when discharge was reduced. Behavioral differences also were observed at different discharge rates, with smolt-size fish exhibiting more directed movement toward the collector during periods of increased discharge. Additionally, the presence of bull trout-size fish may have affected the behavior of smolt-size fish because a greater percentage of smolt-size fish were observed traveling away from the SWW when bull trout-size fish were present than when bull trout-size fish were absent. Increased counts of bull trout-size fish coincided with the increased abundances of smolt-size fish. Overall, the results indicate that smolt-size fish are more abundant near the entrance and in the flume of the SWW during periods of increased discharge, and bull trout-size fish were present at the SWW and may have affected smolt collection.

Oregon↗
USGS2020

Carbon dioxide-induced mortality of four species of North American fishes

Fisheries managers have a growing interest in the use of carbon dioxide (CO 2 ) as a tool for controlling invasive fishes. However, limited published data exist on susceptibility of many commonly encountered species to elevated CO 2 concentrations. Our objective was to estimate the 24-h 50% lethal concentration (LC 50 ) and 95% lethal concentration (LC 95 ) of CO 2 for four fishes (Rainbow Trout Oncorhynchus mykiss , Common Carp Cyprinus carpio , Channel Catfish Ictalurus punctatus , and Westslope Cutthroat Trout Oncorhynchus clarkii lewisi ). In the laboratory, we exposed juvenile fish to a range of CO 2 concentrations for 24 h in unpressurized, flow-through tanks. We developed a Bayesian hierarchical model to estimate the dose-response relationship for each fish species with associated uncertainty, and estimated 24-h LC 50 and LC 95 values based on laboratory trials for each species. The minimum concentration inducing mortality differed among cold water–adapted species and warm water–adapted species groups: 150 mg CO 2 /L for Westslope Cutthroat Trout and Rainbow Trout and 225 mg CO 2 /L for Common Carp and Channel Catfish. We observed complete mortality at 275 mg CO 2 /L (38,672 microatmospheres [μatm]), 225 mg CO 2 /L (30,711 μatm), and 495 mg CO 2 /L (65,708 μatm [Common Carp]; 77,213 μatm [Channel Catfish]) for Westslope Cutthroat Trout, Rainbow Trout, and both Common Carp and Channel Catfish, respectively. There was evidence of a statistical difference between the 24-h LC 95 values of Westslope Cutthroat Trout and Rainbow Trout (245.0 [222.2–272.2] and 190.6 [177.2–207.8] mg CO 2 /L, respectively). Additionally, these values were almost half the estimated 24-h LC 95 values for Common Carp and Channel Catfish (422.5 [374.7–474.5] and 434.2 [377.2–492.2] mg CO 2 /L, respectively). Although the experimental findings show strong relationships between increased CO 2 concentration and higher mortality, additional work is required to assess the efficacy and feasibility of a CO 2 application in a field setting.

Journal of Fish and Wildlife Management↗
USGS2001

Effects of dissolved carbon dioxide on the physiology and behavior of fish artificial streams

A new technology for treating waters contaminated with acid mine drainage involves the dissolution of limestone particles using carbon dioxide at pressures above ambient. Because of the fish health risks associated with episodes of high carbon dioxide levels in treated waters, we subjected three species of fish, brook trout ( Salvelinus fontinalis ), slimy sculpin ( Cottus cognatus ), and blacknose dace ( Rhinichthys atratulus ), to 24 h exposures of elevated dissolved carbon dioxide (CO 2 ) at three levels, ranging from 1.0 (low) to 6.3 (high)%, under laboratory conditions. We measured blood physiological variables as well as behavior, including feeding responses, before, during, and after exposure. Physiological responses differed by species, but all species had elevated hematocrits after 1 h of exposure. Brook trout hematocrits were higher at medium and high levels of CO 2 than in a control group (0.0% CO 2 ) after 24 h of exposure. Slimy sculpin hematocrits were higher in medium- and high-level exposure groups than in controls after 1 h, but not after 24 h, of exposure. Blacknose dace hematocrits were higher in all three exposure groups than in controls after 1 h but only in medium-level exposure groups after 24 h. Brook trout plasma glucose was significantly higher in medium- and high-level exposure groups after 1 h, and in the high-level group after 24 h, than in controls. Slimy sculpin plasma glucose was not significantly different in elevated CO 2 exposure groups from that of controls throughout exposure. Branchial ventilation was significantly greater in all species at elevated CO 2 during exposure, indicating stress; however, no difference was observed between treatment and control groups of blacknose dace after 24 h, indicating acclimation. Pectoral fin beats and cough rates were not consistently related to CO 2 exposure throughout the study. Brook trout had the longest lasting reaction to stress at lower levels of CO 2 among the three species tested. Many of the 11 observed behavioral variables, related to swimming, feeding, social, and illness factors, were affected by elevations of dissolved CO 2 . Two to seven behavioral variables (18–64% of those measured) were affected by treatment level of dissolved CO 2 with a trend by species for the number of variables affected: brook trout>blacknose dace>slimy sculpin. However, behavioral sensitivity to treatment level was greatest in blacknose dace. Recovery to pre-treatment activity rates for most behavior patterns (including feeding) was observed 24 h after cessation of exposure in all three species. Recovery was independent of treatment level, was most rapid in blacknose dace, and was slowest in brook trout. Overall, slimy sculpin was least affected behaviorally by elevated CO 2 . Although all three species showed stress response and changes in behavior at moderate levels of CO 2 (≥2%), brook trout and blacknose dace showed evidence of ability to avoid harmful CO 2 levels by swimming out of affected waters, whereas the slimy sculpin showed minimal behavioral changes despite remaining in place during exposure. Thus, predation risk and other sources of mortality seem minimal in the event of technological malfunction at a stream treatment site involving the use of CO 2 under pressure.

Environmental Toxicology↗
USGS2022

Informing management of Henrys Lake, Idaho using an integrated catch-at-age model

Henrys Lake, Idaho, supports a popular fishery for Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri and Yellowstone Cutthroat Trout × Rainbow Trout O. mykiss hybrids. A majority of the adult population of fish in Henrys Lake are of hatchery origin that were stocked as fingerlings. The fishery is closed to angling during the late winter and spring months, but fisheries managers are considering opening the fishery year-round with catch-and-release-only regulations or with a two-fish bag limit during the extended season. However, there is concern that the proposed management actions may negatively affect the current fishery. Therefore, we developed an integrated catch-at-age model to estimate population parameters for trout in Henrys Lake and used a simulation model to evaluate alternative management actions. Results of this study suggest that catch and release of both Yellowstone Cutthroat Trout and hybrids would increase and that abundance of trout in the spring (i.e., the start of the traditional season) would decrease under both proposed bag limits. Losses in abundance can be mitigated by stocking additional fish as long as no more than approximately 1,520,000 Yellowstone Cutthroat Trout are stocked annually. If catch-and-release-only regulations are implemented during the newly proposed season, total harvest is expected to decrease compared to the current fishery due to additional catch-and-release mortality. Ultimately, managers will need to prioritize harvest or catch-and-release opportunity, both of which provide additional utility to anglers, when choosing how to proceed with bag limit regulations.

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