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At least 433 records · Page 24Linked to original sources

USGS2020

Lake trout growth is sensitive to spring temperature in southwest Alaska lakes

In high‐latitude lakes, air temperature is an important driver of ice cover thickness and duration, which in turn influence water temperature and primary production supporting lake consumers and predators. In lieu of multidecadal observational records necessary to assess the response of lakes to long‐term warming, we used otolith‐based growth records from a long‐lived resident lake fish, lake trout ( Salvelinus namaycush), as a proxy for production. Lake trout were collected from seven deep, oligotrophic lakes in Lake Clark National Park and Preserve on in southwest Alaska that varied in the presence of marine‐derived nutrients (MDN) from anadromous sockeye salmon ( Oncorhynchus nerka) . Linear mixed‐effects models were used to partition variation in lake trout growth by age and calendar‐year and model comparisons tested for a mean increase in lake trout growth with sockeye salmon presence. Year effects from the best mixed‐effects model were subsequently compared to indices of temperature, lake ice, and regional indices of sockeye salmon escapement. A strong positive correlation between annual lake trout growth and temperature suggested that warmer springs, earlier lake ice break‐up, and a longer ice‐free growing season increase lake trout growth via previously identified bottom‐up increases in production with warming. Accounting for differences in the presence or annual escapement of sockeye salmon with available data did not improve model fit. Collectively with other studies, the results suggest that productivity of subarctic lakes has benefitted from warming spring temperatures and that temperature can synchronise otolith growth across lakes with and without sockeye salmon MDN.

Alaska↗

USGS2017

Suppression of invasive lake trout in an isolated backcountry lake in Glacier National Park

Fisheries managers have implemented suppression programmes to control non-native lake trout, Salvelinus namaycush (Walbaum), in several lakes throughout the western United States. This study determined the feasibility of experimentally suppressing lake trout using gillnets in an isolated backcountry lake in Glacier National Park, Montana, USA, for the conservation of threatened bull trout, Salvelinus confluentus (Suckley). The demographics of the lake trout population during suppression (2009–2013) were described, and those data were used to assess the effects of suppression scenarios on population growth rate ( λ ) using an age-structured population model. Model simulations indicated that the population was growing exponentially ( λ = 1.23, 95% CI: 1.16–1.28) prior to suppression. However, suppression resulted in declining λ (0.61–0.79) for lake trout, which was concomitant with stable bull trout adult abundances. Continued suppression at or above observed exploitation levels is needed to ensure continued population declines.

Fisheries Management and Ecology↗

USGS2015

Effects of extreme floods on trout populations and fish communities in a Catskill Mountain river

Summary 1. Extreme hydrologic events are becoming more common with changing climate. Although the impacts of winter and spring ﬂoods on lotic ecosystems have been well studied, the effects of summer ﬂoods are less well known. 2. The Upper Esopus Creek Basin in the Catskill Mountains, NY, experienced severe ﬂooding from Tropical Storm Irene on 28 August 2011, and peak discharges exceeded the 0.01 annual exceedance probability (>100 year ﬂood) in some reaches. Three years of ﬁsh community data from pre-ﬂood surveys at nine sites were compared to data from 2 years of post-ﬂood surveys to evaluate changes in ﬁsh communities and populations of brown trout ( Salmo trutta ) and rainbow trout ( Oncorhynchus mykiss ). 3. Basinwide, ﬁsh assemblages were not strongly impacted and appeared highly resilient to the effects of the ﬂood. Total density and biomass of ﬁsh communities were greater at most sites 10-11 months after the ﬂood than 1 month prior to the ﬂood while richness and diversity were generally unchanged. Community composition did not differ signiﬁcantly between years or between the pre-and post-ﬂood periods. 4. Although the density of mature brown trout was low at most sites (mean density = 146 ﬁsh ha-1), young-of-the-year brown trout reached their highest density (mean = 2312 ﬁsh ha-1) during 2012. In contrast, rainbow trout densities declined substantially during the 5-year study and the 2012 year class was small (mean density = 222 ﬁsh ha-1). 5. Late summer ﬂoods may be less damaging to stream ﬁsh communities than winter or spring ﬂoods as spawning activity is negligible and early life stages of many species are generally larger and less susceptible to displacement and mortality. Additionally, post-ﬂood conditions may be advantageous for brown trout recruitment.

Freshwater Biology↗

USGS2022

Dual resistance to Flavobacterium psychrophilum and Myxobolus cerebralis in rainbow trout (Oncorhynchus mykiss, Walbaum)

Aquatic pathogens are a major concern for fish hatchery production, fisheries management, and conservation, and disease control needs to be addressed. Two important salmonid pathogens are Myxobolus cerebralis and Flavobacterium psychrophilum that cause whirling disease and bacterial coldwater disease (BCWD), respectively. Innate disease resistance is a potential option for reducing disease-related mortality in hatchery-reared rainbow trout ( Oncorhynchus mykiss , Walbaum). Two experiments were conducted to assess pathogen resistance of first-generation (F1) rainbow trout created by crossing M. cerebralis - and F. psychrophilum -resistant strains. In the first experiment, we exposed two rainbow trout strains and one F1 cross to six treatments: control (no exposure), mock injection, F. psychrophilum only, M. cerebralis only, F. psychrophilum then M. cerebralis , and M. cerebralis then F. psychrophilum . Results indicated that the F1 cross was not resistant to either pathogen. In the second experiment, we exposed five rainbow trout strains and four rainbow trout crosses to F. psychrophilum . The second experiment indicated that at least one rainbow trout cross was F . psychrophilum -resistant. Achieving dual resistance may be possible using selective breeding but only some multigenerational strains are suitable candidates for further evaluation.

Journal of Fish Diseases↗

USGS2021

Influence of water temperature and biotic interactions on the distribution of westslope cutthroat trout (Oncorhynchus clarkii lewisi) in a population stronghold under climate change

Climate warming is expected to have substantial impacts on native trout across the Rocky Mountains, but there is little understanding of how these changes affect future distributions of co-occurring native fishes within population strongholds. We used mixed-effects logistic regression to investigate the role of abiotic (e.g., temperature) and biotic factors (bull trout presence, Salvelinus confluentus ) on distributions of westslope cutthroat trout ( Oncorhynchus clarkii lewisi ; WCT) in the North Fork Flathead River, USA and Canada. The probability of WCT presence increased with stream temperature and decreased with channel gradient and bull trout presence, yet the effect of bull trout was reduced with increasing pool densities. Combining this model with spatially explicit stream temperature projections, we predict a 29% increase in suitable habitat under high emissions through 2075, with gains at mid-elevation sites predicted to exceed bull trout thermal tolerances and high-elevation sites expected to become more thermally suitable for WCT. Our study illustrates the importance of considering abiotic and biotic drivers to assess species response to climate change, helping to guide local-scale climate adaptation and management.

Alberta, British Columbia, Montana↗

USGS2023

A generalized application of the catch-curve regression with comparisons of adult mortality and year-class strength between hatchery-stocked and wild-reared lake trout in US waters of Lake Huron

The recently developed approach to estimating the instantaneous total mortality of coded-wire-tagged lake trout ( Salvelinus namaycush ) is generally applicable to catch-at-age data. We further formalized the technique to objectively incorporate the year-class and year effects into the model structure of catch-curve regression. We used this new method to compare adult mortality and year-class strength between the hatchery-stocked and wild-reared lake trout in US waters of Lake Huron, one of the Laurentian Great Lakes. Model comparisons showed no difference in adult mortality between the hatchery-stocked and wild-reared lake trout. Based on 95% confidence intervals, the estimate of adult mortality using the simple catch-curve regression with average number-at-age was not statistically different from the estimate using the linear mixed model with individual number-at-age of multiple year-classes and sampling years. The linear mixed model, however, also quantified lake trout year-class strength and indicated that since 2003, the increases in recruitment of wild-reared lake trout did not fully compensate for the rapid declines in recruitment of hatchery-stocked lake trout in Lake Huron.

Lake Huron↗

USGS2025

Negative growth in body mass of trout and salmon in a small stream network

In species inhabiting stressful environments, some individuals experience negative growth in body mass during their lives, potentially influencing survival, reproduction, populations, and ecosystems. Using data from a long-term (1997–2015) study of brook trout ( Salvelinus fontinalis ), brown trout ( Salmo trutta ), and juvenile Atlantic salmon ( Salmo salar ) in Massachusetts, USA, we analyzed the frequency, causes, and consequences of seasonal mass loss. Negative growth occurred in 14.8% of observations (3573 instances), with the highest prevalence during summer (June–September). Species differed markedly: 42.5% of juvenile Atlantic salmon, 24.9% of brook trout, but only 7.7% of brown trout exhibited negative growth. The likelihood of mass loss increased with size, age, and low stream flows, particularly in summer. Brook trout in the small or isolated tributaries exhibited less summer mass loss than those in the larger streams. Other factors, including temperature and population density, had minimal or inconsistent effects. Individuals experiencing negative growth, especially brook trout in summer and autumn, were less likely to be re-encountered. As we observed no association of mass loss with movement, this suggests a potential survival cost of negative body mass growth.

Massachusetts↗

USGS2012

Estimating recruitment dynamics and movement of rainbow trout ( Oncorhynchus mykiss ) in the Colorado River in Grand Canyon using an integrated assessment model

We used an integrated assessment model to examine effects of flow from Glen Canyon Dam, Arizona, USA, on recruitment of nonnative rainbow trout ( Oncorhynchus mykiss ) in the Colorado River and to estimate downstream migration from Glen Canyon to Marble Canyon, a reach used by endangered native fish. Over a 20-year period, recruitment of rainbow trout in Glen Canyon increased with the annual flow volume and when hourly flow variation was reduced and after two of three controlled floods. The model predicted that approximately 16 000 trout·year –1 emigrated to Marble Canyon and that the majority of trout in this reach originate from Glen Canyon. For most models that were examined, over 70% of the variation in emigration rates was explained by variation in recruitment in Glen Canyon, suggesting that flow from the dam controls in large part the extent of potential negative interactions between rainbow trout and native fish. Controlled floods and steadier flows, which were originally aimed at partially restoring conditions before the dam (greater native fish abundance and larger sand bars), appear to have been more beneficial to nonnative rainbow trout than to native fish.

Arizona↗

USGS1993

Accumulation of PCBs by lake trout ( Salvelinus namaycush ): an individual-based model approach

To explain the variation in growth and in concentration of polychlorinated biphenyls (PCBs) among individual fish, an individual-based model (IBM) was applied to the lake trout ( Salvelinus namaycush ) population in Lake Michigan. The IBM accurately represented the variation in growth exhibited by the different age classes of lake trout. Uncertainty analysis of the IBM revealed that mean PCB concentration for the lake trout population was most sensitive to PCB concentration in their prey. The variability in PCB concentration among lake trout individuals was not adequately explained by the IBM, unless variation in prey fish PCBs was included in the model. To accomplish this, the simulated lake trout population was divided into subsets subjected to different levels of PCB concentration in the prey fish. Thus, model results indicated that variability in prey fish PCB concentration was an important component of the variation in PCB concnetration observed among individual lake trout comprising the Lake Michigan population.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS1996

Predation by sea lamprey (Petromyzon marinus) on lake trout (Salvelinus namaycush) in southern Lake Ontario, 1982-1992

Dead lake trout ( Salvelinus namaycush ) killed by sea lamprey (P etromyzon marinus ) were collected from the bottom of Lake Ontario using bottom trawls. The number of dead lake trout per hectare could be predicted from the number of type A-1 sea lamprey marks observed on live fish in September gillnet surveys ( r 2 = 0.60, P < 0.01) but not from the sum of marks of types A-1, A-2, and A-3 combined. Sea lamprey selectively attacked and killed the largest lake trout. The lengths and ages of live fish with A-1 marks increased as the population of longer, older lake trout in the lake increased, and the length distributions of fish killed by sea lamprey were not different ( P > 0.05) from those of live fish with A-1 marks in 5 of 6 years where comparisons could be made. Compared with Lake Superior strain lake trout, Seneca Lake strain fish were only 0.41 times as likely to be attacked by sea lamprey and were less likely to die from an attack (both differences P < 0.05). Conservative estimates of the numbers of lake trout killed by sea lamprey in southern Lake Ontario from October to mid-November ranged from 17,000 in 1988 to 121,000 in 1984.

New York, Ontario↗

USGS2014

Survival and reproduction of myxobolus cerebralis-resistant Rainbow Trout introduced to the colorado river and increased resistance of age-0 progeny

Myxobolus cerebralis caused severe declines in rainbow trout populations across Colorado following its introduction in the 1980s. One promising approach for the recovery of Colorado’s rainbow trout populations has been the production of rainbow trout that are genetically resistant to the parasite. We introduced one of these resistant crosses, known as the GR×CRR (cross between the German Rainbow [GR] and Colorado River Rainbow [CRR] trout strains), to the upper Colorado River. The abundance, survival, and growth of the stocked GR×CRR population was examined to determine if GR×CRRs had contributed offspring to the age-0 population, and determine whether these offspring displayed increased resistance and survival characteristics compared to their wild CRR counterparts. Apparent survival of the introduced GR×CRR over the entire study period was estimated to be 0.007 (±0.001). Despite low survival of the GR×CRRs, age-0 progeny of the GR×CRR were encountered in years 2008 through 2011. Genetic assignments revealed a shift in the genetic composition of the rainbow trout fry population over time, with CRR fish comprising the entirety of the fry population in 2007, and GR-cross fish comprising nearly 80% of the fry population in 2011. A decrease in average infection severity (myxospores fish −1 ) was observed concurrent with the shift in the genetic composition of the rainbow trout fry population, decreasing from an average of 47,708 (±8,950) myxospores fish −1 in 2009 to 2,672 (±4,379) myxospores fish −1 in 2011. Results from this experiment suggest that the GR×CRR can survive and reproduce in rivers with a high prevalence of M. cerebralis . In addition, reduced myxospore burdens in age-0 fish indicated that stocking this cross may ultimately lead to an overall reduction in infection prevalence and severity in the salmonid populations of the upper Colorado River.

Arizona, California, Colorado, New Mexico, Utah, W↗

USGS2015

Local variability mediates vulnerability of trout populations to land use and climate change

Land use and climate change occur simultaneously around the globe. Fully understanding their separate and combined effects requires a mechanistic understanding at the local scale where their effects are ultimately realized. Here we applied an individual-based model of fish population dynamics to evaluate the role of local stream variability in modifying responses of Coastal Cutthroat Trout ( Oncorhynchus clarkii clarkii ) to scenarios simulating identical changes in temperature and stream flows linked to forest harvest, climate change, and their combined effects over six decades. We parameterized the model for four neighboring streams located in a forested headwater catchment in northwestern Oregon, USA with multi-year, daily measurements of stream temperature, flow, and turbidity (2007–2011), and field measurements of both instream habitat structure and three years of annual trout population estimates. Model simulations revealed that variability in habitat conditions among streams (depth, available habitat) mediated the effects of forest harvest and climate change. Net effects for most simulated trout responses were different from or less than the sum of their separate scenarios. In some cases, forest harvest countered the effects of climate change through increased summer flow. Climate change most strongly influenced trout (earlier fry emergence, reductions in biomass of older trout, increased biomass of young-of-year), but these changes did not consistently translate into reductions in biomass over time. Forest harvest, in contrast, produced fewer and less consistent responses in trout. Earlier fry emergence driven by climate change was the most consistent simulated response, whereas survival, growth, and biomass were inconsistent. Overall our findings indicate a host of local processes can strongly influence how populations respond to broad scale effects of land use and climate change.

Oregon↗

USGS2020

Concealment of juvenile bull trout in response to temperature, light, and substrate: Implications for detection

Bull trout ( Salvelinus confluentus) are challenging to detect as a result of the species cryptic behavior and coloration, relatively low densities in complex habitats, and affinity for cold, high clarity, low conductivity waters. Bull trout are also closely associated with the stream bed, frequently conceal in substrate, and this concealment behavior is poorly understood. Consequently, population assessments are problematic and biologists and managers often lack quantitative information to accurately describe bull trout distributions, estimate abundance, and assess status and trends; particularly for stream-dwelling populations. During controlled laboratory trials, we recorded concealment, resting, and swimming behavior of juvenile wild bull trout in response to: (1) constant and fluctuating water temperature, (2) presence or absence of light, and (3) substrate size. Light level had the strongest influence on wild fish concealment and more fish concealed as light levels increased from darkness to daylight. Wild fish were 14.5 times less likely to conceal in constant darkness and 4.1 times more likely to conceal in 12 h light x 12 h darkness compared to constant light. Wild fish were 6.2 times less likely to conceal in small (26–51 mm) substrate compared to larger (52–102 mm) substrate. As water temperature increased, fewer wild fish concealed. Knowledge of wild bull trout concealment will improve field sampling protocols and increase detection efficiencies. These data also enhance knowledge of bull trout niche requirements which illuminates ecological differences among species and informs conservation and restoration efforts.

PLoS ONE↗

USGS1952

Further studies on factors determining tissue levels of sulfamerazine in trout

There is considerable variation in the tissue level of sulfamerazine among individual trout in a treated population. This fact may be the reason why prolonged sulfonamide therapy sometimes fails to free all trout from Bacterium salmonicida. The quantity of food given with a standard dosage of sulfamerazine has a pronounced effect on the tissue concentration of sulfamerazine; the concentration increased when the quantity of food decreased. It appears therefore, that trout should be fed at a rate very closely adjusted to their optimum feeding requirements for the best practical results. The start of treatment with high initial doses of sulfamerazine had no effect on the tissue concentration sustained by the maintenance dosage. The relative distribution of sulfamerazine in various organs and tissues of rainbow trout was about the same as in brown and brook trout. The only difference noticed was the lack of peak levels of short duration between the 8 and 10 days of treatment, which is characteristic for brook and brown trout.

Transactions of the American Fisheries Society↗

USGS1969

Bacteria in blood and kidney of apparently healthy hatchery trout

Aseptic examination of blood and kidney material from three species of apparently healthy trout at two hatcheries showed that 12.5% of examined trout at one hatchery and 26.1% of trout at the other carried low numbers of bacteria. In addition, sera from these trout had agglutinins against some of the isolated bacteria and bacterial types found in trout were the same as those cultured from raceway water in which fish were raised. Although the presence of these bacteria does not constitute a disease state, the potential for an epizootic is present should trout be placed under stress conditions.

Transactions of the American Fisheries Society↗

USGS1997

Geomorphic influences on the distribution of Yellowstone cutthroat trout in the Absaroka Mountains, Wyoming

Influences of large‐scale abiotic, geomorphic characteristics on distributions of Yellowstone cutthroat trout Oncorhynchus clarki bouvieri are poorly understood. We sampled 151 sites on 56 perennial streams in the Greybull–Wood river drainage in northwestern Wyoming to determine the effects of geomorphic variables on Yellowstone cutthroat trout distributions. Channel slope, elevation, stream size, and barriers to upstream movement significantly influenced the presence and absence of Yellowstone cutthroat trout. Wild populations of Yellowstone cutthroat trout were not found upstream of barriers to fish migration, at sites with channel slopes of 10% or greater, or at elevations above 3,182 m. Based on channel slope alone, logistic regression models correctly classified presence or absence of Yellowstone cutthroat trout in 83% of study sites. The addition of elevation and stream size in the models increased classification to 87%. Logistic models tested on an independent data set had agreement rates as high as 91 % between actual and predicted fish presence. Large‐scale geomorphic variables influence Yellowstone cutthroat trout distributions, and logistic functions can predict these distributions with a high degree of accuracy.

Wyoming↗

USGS1999

A blood chemistry profile for lake trout

A blood chemistry profile for lake trout Salvelinus namaycush was developed by establishing baseline ranges for several clinical chemistry tests (glucose, total protein, amylase, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, creatine kinase, calcium, and magnesium). Measurements were made accurately and rapidly with a Kodak Ektachem DT60 Analyzer and the Ektachem DTSC Module. Blood serum was collected from both laboratory-reared lake trout (1978 and 1986 year-classes) and feral spawning trout from Lake Michigan and then analyzed in the laboratory. No clinically significant differences were found between samples analyzed fresh and those frozen for 1 or 6 weeks. The ranges in chemistry variables for feral lake trout were generally wider than those for laboratory-reared lake trout, and significant differences existed between male and female feral lake trout for several tests. Blood chemistry profiles also varied seasonally on fish sampled repeatedly.

Journal of Aquatic Animal Health↗

USGS2001

Lack of selection for resistance to whirling disease among progeny of Colorado River rainbow trout

We compared the resistance to whirling disease of two groups of Colorado River rainbow trout Oncorhynchus mykiss and a domestic strain of rainbow trout in a controlled laboratory challenge. These three groups represented the progeny of wild rainbow trout known to have recruited (1) during the early years of infestation by Myxobolus cerebralis of the Colorado River or (2) before the presence of M. cerebralis in the system and (3) the Erwin strain of rainbow trout. The severity of whirling disease in each group was dependent on the dose of triactinomyxons of M. cerebralis to which the fish were exposed. Microscopic lesions and spore counts both increased with increasing parasite dose. Survival of the progeny of Colorado fish that recruited before the presence of M. cerebralis in the system was significantly less than was that of the domestic fish exposed to 0 and 1,000 triactinomyxons/fish. The parents that recruited to the system before the presence of M. cerebralis were considerably older than were those used for our domestic strain; this difference in parent age probably resulted in the difference in survival because egg quality decreases with age in rainbow trout. There was no difference in microscopic lesions, spore counts, or swimming performance among the three groups of rainbow trout when exposed at the same parasite level, indicating that there was no difference in resistance to whirling disease among these groups of fish.

Journal of Aquatic Animal Health↗