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At least 199 records · Page 11Linked to original sources
USGS2023

Developing fluvial fish species distribution models across the conterminous United States—A framework for management and conservation

This report explains the steps and specific methods used to predict fluvial fish occurrences in their native ranges for the conterminous United States. In this study, boosted regression tree models predict distributions of 271 ecologically important fluvial fish species using relations between fish presence/absence and 22 natural and anthropogenic landscape variables. Models developed for the freshwater portions of the ranges for species represented 28 families. Cyprinidae was the family with the most species (87 of 271) modeled for this study, followed by Percidae (34) and Ictaluridae (17). Model predictive performance was evaluated using four metrics: area under the receiver operating characteristic curve, sensitivity, specificity, and True Skill Statistic, which are all from tenfold cross-validation results. The relative importance of the predictor variables in the boosted regression tree models was calculated and ranked for each species. The three strongest natural predictors of fish distributions were network catchment area, the mean annual air temperature of the local catchment, and the maximum elevation of the local catchment, while the three strongest anthropogenic predictors were downstream main stem dam density, distance to downstream main stem dam, and the percentage of pasture/hay land use area within network catchment boundaries. Study results showed 61 fish species were sensitive to climate variables, and 40 fish species were sensitive to anthropogenic stressors. The models developed in this study can be used to derive critical information regarding habitat protection priorities, anthropogenic threats, and potential effects of climate change on habitat suitability, aiding in efforts to conserve fluvial fishes now and into the future.

Conterminous United States↗
USGS2019

Phylogeny and foraging mode correspond with thiaminase activity in freshwater fishes: Potential links to environmental factors

Knowledge of the dietary components of fish species is important for understanding their growth, survival, and recruitment. Deficiency in thiamine (vitamin B1) leading to reproductive failure and physiological illness among freshwater fishes has been attributed to thiaminase activity in fish in the Great Lakes and the New York Finger Lakes, but the causes of variation in thiaminase activity among freshwater fishes is unclear. We characterized thiaminase activity in 29 species of freshwater fishes across 7 ray-finned and 1 jawless family. All fish were further categorized by phylogeny, trophic category (trophic level and feeding mode), and native or non-native status to evaluate how ecological processes correspond with thiaminase activity. Thiaminase activity varied significantly across species, families, trophic factors, phylogenetic groups, and sites. Teleosts that were more recently derived had higher thiaminase activity than more basal species. Thiaminase activity was also higher among herbivores than omnivores or carnivores. This trend was clearest in the Cyprinidae family, which had the greatest range in thiaminase activity and a wide range in trophic-level position and trophic categories (herbivores, omnivores, and carnivores). Variation in average thiaminase activity of Spotfin Shiners (Cyprinella spiloptera) among sites within a watershed was correlated with anthropogenic and natural components of land cover. Our study contributes much-needed quantitative ecological information related to thiaminase activity in a suite of fish species that vary in evolutionary history, trophic level, and foraging modes. However, more studies are needed to identify interacting causes of thiaminase variation and examine the implications of these findings on the overall health of aquatic populations and freshwater ecosystems.

Freshwater Science↗
USGS2026

A conceptual framework and methods for studying the connectivity of fishes

Connectivity is a multifaceted concept that has important implications for the management and conservation of marine and freshwater fishes. We developed a conceptual framework that encompasses multiple, interrelated categories of connectedness, including landscape (e.g., structural, functional) connectivity and ecological (e.g., trophic, genetic, demographic) connectivity, that together shape the flow of organisms, energy and information across ecosystems. We also synthesised six key methods that can be used to study connectivity of fishes: (1) telemetry, including satellite, acoustic, radio and passive integrated transponders (PIT), (2) mark-recapture, (3) environmental tracers, including stable isotopes and otolith-microchemistry, (4) genetics, (5) community structure analysis and (6) emerging technologies and tools (e.g., remote sensing and artificial intelligence). For each method, we describe the categories of connectivity it can assess and provide real-world examples where they have been effectively used. We also identify limitations of each method. This article highlights the diverse and evolving toolbox of methods used to assess fish connectivity, underscoring the need for continued collaboration, innovation and integration of new approaches to refine our understanding and address remaining challenges in this critical area of aquatic ecology and fisheries management.

Fish and Fisheries↗
USGS2014

Spatiotemporal associations of reservoir nutrient characteristics and the invasive, harmful alga Prymnesium parvum in West Texas

Golden alga ( Prymnesium parvum ) is a harmful alga that has caused ecological and economic harm in freshwater and marine systems worldwide. In inland systems of North America, toxic blooms have nearly eliminated fish populations in some systems. Modifying nutrient profiles through alterations to land or water use may be a viable alternative for golden alga control in reservoirs. The main objective of this study was to improve our understanding of the nutrient dynamics that influence golden alga bloom formation and toxicity in west Texas reservoirs. We examined eight sites in the Upper Colorado River basin, Texas: three impacted reservoirs that have experienced repeated golden alga blooms; two reference reservoirs where golden alga is present but nontoxic; and three confluence sites downstream of the impacted and reference sites. Total, inorganic, and organic nitrogen and phosphorus and their ratios were quantified monthly along with golden alga abundance and ichthyotoxicity between December 2010 and July 2011. Blooms persisted for several months at the impacted sites, which were characterized by high organic nitrogen and low inorganic nitrogen. At impacted sites, abundance was positively associated with inorganic phosphorus and bloom termination coincided with increases in inorganic nitrogen and decreases in inorganic phosphorus in late spring. Management of both inorganic and organic forms of nutrients may create conditions in reservoirs unfavorable to golden alga.

Journal of the American Water Resources Associatio↗
USGS2018

Biological and ecological science for Michigan—The Great Lakes State

Michigan is rich in lakes, rivers, dune and rocky shorelines, forests, fish and wildlife, and has the longest freshwater coastline in the United States, 3,224 miles. Many enterprises critical to Michigan’s economy and cultural heritage are based on natural resources including commercial and sport fishing, hunting, and other outdoor recreation. Overall, outdoor recreation is enjoyed by more than 63 percent of Michigan residents, and has been estimated to generate $18.7 billion in consumer spending, create 194,000 jobs, and raise $1.4 billion in State and local tax revenue annually.

Michigan↗
USGS2014

Mercury in fishes from 21 national parks in the Western United States: inter- and intra-park variation in concentrations and ecological risk

Mercury (Hg) is a global contaminant and human activities have increased atmospheric Hg concentrations 3- to 5-fold during the past 150 years. This increased release into the atmosphere has resulted in elevated loadings to aquatic habitats where biogeochemical processes promote the microbial conversion of inorganic Hg to methylmercury, the bioavailable form of Hg. The physicochemical properties of Hg and its complex environmental cycle have resulted in some of the most remote and protected areas of the world becoming contaminated with Hg concentrations that threaten ecosystem and human health. The national park network in the United States is comprised of some of the most pristine and sensitive wilderness in North America. There is concern that via global distribution, Hg contamination could threaten the ecological integrity of aquatic communities in the parks and the wildlife that depends on them. In this study, we examined Hg concentrations in non-migratory freshwater fish in 86 sites across 21 national parks in the Western United States. We report Hg concentrations of more than 1,400 fish collected in waters extending over a 4,000 kilometer distance, from Alaska to the arid Southwest. Across all parks, sites, and species, fish total Hg (THg) concentrations ranged from 9.9 to 1,109 nanograms per gram wet weight (ng/g ww) with a mean of 77.7 ng/g ww. We found substantial variation in fish THg concentrations among and within parks, suggesting that patterns of Hg risk are driven by processes occurring at a combination of scales. Additionally, variation (up to 20-fold) in site-specific fish THg concentrations within individual parks suggests that more intensive sampling in some parks will be required to effectively characterize Hg contamination in western national parks. Across all fish sampled, only 5 percent had THg concentrations exceeding a benchmark (200 ng/g ww) associated with toxic responses within the fish themselves. However, Hg concentrations in 35 percent of fish sampled were above a benchmark for risk to highly sensitive avian consumers (90 ng/g ww), and THg concentrations in 68 percent of fish sampled were above exposure levels recommended by the Great Lakes Advisory Group (50 ng/g ww) for unlimited consumption by humans. Of the fish assessed for risk to human consumers (that is, species that are large enough to be consumed by recreational or subsistence anglers), only one individual fish from Yosemite National Park had a muscle Hg concentration exceeding the benchmark (950 ng/g ww) at which no human consumption is advised. Zion, Capital Reef, Wrangell-St. Elias, and Lake Clark National Parks all contained sites in which most fish exceeded benchmarks for the protection of human and wildlife health. This finding is particularly concerning in Zion and Capitol Reef National Parks because the fish from these parks were speckled dace, a small, invertebrate-feeding species, yet their Hg concentrations were as high or higher than those in the largest, long-lived predatory species, such as lake trout. Future targeted research and monitoring across park habitats would help identify patterns of Hg distribution across the landscape and facilitate management decisions aimed at reducing the ecological risk posed by Hg contamination in sensitive ecosystems protected by the National Park Service.

Alaska;Arizona;California;Colorado;Idaho;Montana;N↗
USGS2013

Introduction to a special section: Ecology, culture, and management of Burbot

The Burbot Lota lota is the only truly freshwater member of the cod family (Gadidae) and one of only two species of freshwater fish that have a circumpolar range (McPhail and Lindsey 1970; McPhail and Paragamian 2000). Two subspecies of Lota lota have been documented: Lota lota maculosa, which is found exclusively in North America from south of Great Slave Lake in Canada to the southern limit of its range; and Lota lota lota, which is found over the remainder of the species’ Nearctic range and its entire Eurasian range (Hubbs and Schultz 1941; Van Houdt et al. 2003). However, many recent authorities (e.g., Scott and Crossman 1973) do not designate subspecies. Burbot occupy the widest range of depths of all fishes found in the Laurentian Great Lakes basin (i.e., from small streams to at least 300 m in Lake Superior; Boyer et al. 1989). Worldwide, many Burbot populations are threatened or endangered or have been extirpated (reviewed by Stapanian et al. 2010). Due in part to its unpopularity as a sport and commercial fish in much of its range, the species is often ignored in fish management and conservation programs (McPhail and Paragamian 2000; Stapanian et al. 2008, 2010). Even basic information on Burbot ecology, particularly its early life history and spawning habitats and sites, is lacking. This lack of information is particularly troubling because Burbot are an indicator of the health of coldwater systems (Stapanian et al. 2010). Efforts to rehabilitate or restore imperiled populations include culturing early life stages. Burbot larvae are difficult to culture for a variety of reasons, including their delicate body structure, small size at hatch, and live-feed requirement for at least 5 weeks following alimentary tract development.

Transactions of the American Fisheries Society↗
USGS2013

Beaver dams maintain fish biodiversity by increasing habitat heterogeneity throughout a low-gradient stream network

Understanding the relationship between heterogeneity and biodiversity is an active focus of ecological research. Although habitat heterogeneity is conceptually linked to biodiversity, the amount and configuration of heterogeneity that maintains biodiversity within ecosystems is not well understood, especially for an entire stream network. Here, we tested alternative outcomes about how habitat alterations caused by beaver dams affected native fish biodiversity. Specifically, we quantified in-stream habitat and fish assemblages above and below all beaver dams ( n = 15) and selected control sites ( n = 9), adjacent to beaver dams, within an entire, low-gradient stream network (Fish Brook, MA, U.S.A.). Beaver dams altered habitat within streams in four ways based on upstream versus downstream differences in stream width, depth, velocity and substratum. In general, habitat heterogeneity, measured using two indices, was greater at beaver dams than control sites. The diversity and abundance of fish around beaver dams were positively related to habitat heterogeneity. Faster water and the coarser substratum below beaver dams increased the amount of fluvial habitat available to native fish. This alteration can be critical for fish with life histories that depend on flowing water and hard substrata. In summary, within a stream network, beaver dams maintained fish biodiversity by altering in-stream habitat and increasing habitat heterogeneity. Understanding the relationship between habitat heterogeneity and biodiversity can advance basic freshwater ecology and provide science-based support for applied aquatic conservation

Massachusetts↗
USGS2026

Small creatures, big challenge: A review of current knowledge and assessment of research needs to inform water withdrawal management for the Duck River's freshwater mussel fauna

The Duck River is a remarkable national resource, boasting outstanding biodiversity (Ahlstedt et al. 2017). It contains 151 fish species, over 60 mussel species, and 22 snail species, many of which are federally listed (Etnier and Starnes 1993; Johnson et al. 2013; Ahlstedt et al. 2017; Womble and Rosenberger 2025a). The Duck River watershed is at a pivotal time in its management and ecological history due to significant growth in human population and economic activity. The consequent increase in surface water demand presents challenges for sustainable water resource management. The Tennessee Department of Environment and Conservation (TDEC) has permitted or proposed to permit eight water utilities to withdraw over 77 million gallons per day (mgd) from the Duck River, representing > 40% increase from previously permitted amounts (USFWS 2025). On November 20, 2024, Tennessee Governor Bill Lee signed Executive Order No 108 to ensure long-term stability of the Duck River watershed through balancing economic growth, water resource management, and environmental conservation. Some primary components of this plan are the creation of a Comprehensive Regional Drought Management Plan, the development of a Habitat Conservation Plan, and the establishment of the Duck River Watershed Planning Partnership (DRWPP). Although the planning partnership is not focused on a sole aspect of the Duck River, but the watershed as a whole, the mussel assemblages of the Duck River have been a particular focus due to their importance in providing ecosystem services, sensitivity to water quality, conservation status, and sensitivity to periodic drought conditions in this system. With multiple state and federal agencies involved in managing the Duck River’s unique water resources, a focused review on how future water management could affect the freshwater mussel communities in the Duck River will contribute to this process. Our objectives of this review are to: 1. Review the effects of changing flow regimes on mussels, with emphasis on the effect of droughts/low flows, highlighting key processes/factors affecting mussels. 2. Highlight critical data gaps that could allow future, evidence-based water management decisions in this system. 3. Propose research topics to address critical data gaps and enable evidence-based water management decisions that consider the needs of freshwater mussels. Freshwater mussels are a critical component of riverine ecosystems, providing ecosystem services including water filtration, nutrient cycling, and habitat provision (Vaughn et al. 2004; Haag 2012) that benefit human communities. Environmental flows, also referred to as ecological or e-flows, refer to the quantity, timing, and quality of water flows necessary to maintain the ecological health of rivers, wetlands, and other aquatic ecosystems (Acreman and Dunbar 2004; Acreman 2016). For freshwater mussels, environmental flows include maintaining a flow regime and associated water quality regimes that are favorable for both juveniles and adults while also seasonally supporting host fish and the survival of settling glochidia (i.e., larval mussels) in suitable environments (Gates et al. 2015). Freshwater mussels are adapted to the natural flow regime of their native streams, including seasonal variability in flows. As sedentary filter feeders, mussels require adequate water flow to provide oxygen and food (Allen and Vaughn 2009); however, they also require periods of low flow to increase access to fish hosts and to ensure juveniles are not displaced (Gates et al 2015). Mussels are sensitive to water quality conditions, including pollutants, sedimentation, and artificial alterations of temperature and pH (Strayer and Malcom 2012). Mussel community characteristics, including presence, abundance, and species richness, generally increase with stream size (e.g., stream order); however, responses to changes in flow conditions are often species-specific, and the magnitude and timing of extreme flow conditions have more predictive power for mussel community response than general changes in flow (Lopez and Vaughn 2021). Complex hydraulic variables, such as relative shear stress and Reynolds number, can be strong predictors of mussel community responses because they combine simple hydraulic variables (e.g., velocity, depth) with stream channel characteristics, such as substrate composition and dynamics. Droughts directly and indirectly affect mussels by influencing their physiology, behavior, reproduction, and ecosystem roles. Mass mussel die-offs during droughts and low water conditions are widely documented (Vaughn et al. 2015; Sousa et al. 2018; Dubose et al. 2019). Droughts can also lead to a shift in mussel community composition, with drought-tolerant species becoming more dominant while more sensitive species experience declines (Galbraith et al, 2010; Lopez et al. 2022; Vaughn and Atkinson 2025). Droughts affect mussels through direct mortality from stranding as well as physiological stress from altered water temperature and quality, reduced habitat and food availability and quality, increased predation and competition, disruption of reproductive cycles, and increased susceptibility to disease and pathogens. Although the effects of droughts, water withdrawals, and low flow conditions on mussels are an increasing area of study, there is a general paucity of data-driven consensus regarding optimal mitigation approaches and strategies (Cushway et al. 2024). Long-term management decisions regarding water withdrawals, particularly during extended or multi-year drought conditions, may consider factors beyond direct mortality such as the sublethal effects of drought and low flow conditions on freshwater mussels for a comprehensive understanding of the effects of prolonged low flows on freshwater mussels and aquatic communities.

Tennessee↗
USGS2019

Consistent compensatory growth offsets poor condition in trout populations

1. Compensatory growth – when individuals in poor condition grow rapidly to “catch up” to conspecifics – may be a mechanism that allows individuals to tolerate stressful environmental conditions, both abiotic and biotic. This phenomenon has been documented fairly widely in laboratory and field experiments, but evidence for compensatory growth in the wild is scarce. 2. Cutthroat trout (Oncorhynchus clarkii subsp) are cold-water specialists that inhabit streams in montane ecosystems where seasonal conditions can be harsh and growth rates vary greatly among seasons. Understanding if individuals compensate for periods of reduced growth and body condition will improve understanding of the requirements of fish throughout their life-cycle and across freshwater habitats. 3. We quantified compensatory growth of juvenile cutthroat trout using extensive mark-recapture data from 11 stream populations (1,125 individuals) and two subspecies inhabiting a wide range of ecological settings in the northern Rocky Mountains, USA. Our objectives were to determine how growth was linked across seasons and determine if individuals behaviorally compensated for depressed body condition via emigration. 4. Fish in relatively poor condition consistently demonstrated compensatory growth in mass during subsequent seasons. In contrast, fish in relatively better condition responded with positive growth in length during the summer signaling these fish may be better suited to headwater environments; no compensatory growth in length was found during the winter. Furthermore, we found no evidence that individual condition mediated migration tendencies of fish to seek more favorable habitat. 5. Across a wide range of environmental conditions, we found consistent empirical support for compensatory growth in mass in the wild. A critical next step is to quantify how changing abiotic and biotic conditions influence the ability of stream fishes to compensate for locally or seasonally challenging conditions, thereby affecting long-term resiliency, viability, and adaptation in the face of changing environmental conditions.

Montana, Wyoming↗
USGS2010

Hydrological connectivity for riverine fish: measurement challenges and research opportunities

In this review, we first summarize how hydrologic connectivity has been studied for riverine fish capable of moving long distances, and then identify research opportunities that have clear conservation significance. Migratory species, such as anadromous salmonids, are good model organisms for understanding ecological connectivity in rivers because the spatial scale over which movements occur among freshwater habitats is large enough to be easily observed with available techniques; they are often economically or culturally valuable with habitats that can be easily fragmented by human activities; and they integrate landscape conditions from multiple surrounding catchment(s) with in‐river conditions. Studies have focussed on three themes: (i) relatively stable connections (connections controlled by processes that act over broad spatio‐temporal scales >1000 km 2 and >100 years); (ii) dynamic connections (connections controlled by processes acting over fine to moderate spatio‐temporal scales ∼1–1000 km 2 and <1–100 years); and (iii) anthropogenic influences on hydrologic connectivity, including actions that disrupt or enhance natural connections experienced by fish. We outline eight challenges to understanding the role of connectivity in riverine fish ecology, organized under three foci: (i) addressing the constraints of river structure; (ii) embracing temporal complexity in hydrologic connectivity; and (iii) managing connectivity for riverine fishes. Challenges include the spatial structure of stream networks, the force and direction of flow, scale‐dependence of connectivity, shifting boundaries, complexity of behaviour and life histories and quantifying anthropogenic influence on connectivity and aligning management goals. As we discuss each challenge, we summarize relevant approaches in the literature and provide additional suggestions for improving research and management of connectivity for riverine fishes. Specifically, we suggest that rapid advances are possible in the following arenas: (i) incorporating network structure and river discharge into analyses; (ii) increasing explicit consideration of temporal complexity and fish behaviour in the scope of analyses; and (iii) parsing degrees of human and natural influences on connectivity and defining acceptable alterations. Multiscale analyses are most likely to identify dominant patterns of connections and disconnections, and the appropriate scale at which to focus conservation activities.

Freshwater Biology↗
USGS2024

Peering into the eye of the sea lamprey: What can stable isotopes in lamprey eye lenses reveal about their life history?

The Atlantic sea lamprey ( Petromyzon marinus ) is an anadromous species which is a detritivore for years in freshwater, before metamorphosing into a juvenile and feeding parasitically at sea. However, their migratory patterns and marine ecology are poorly characterized. In other fishes, chemical analysis of calcified structures has aided in understanding their life history, but sea lamprey lacks these structures. Recent work using eye lenses suggests an alternate approach. Lenses are stable protein structures that accrue layers on their outer edge as they grow. We used stable isotope ratios (δ x Y) of hydrogen, carbon, nitrogen, and oxygen to explore lens layers and compare lenses to muscle. Returning adults were collected in May 2021 from the Penobscot (Maine), Connecticut (Massachusetts), and Susquehanna (Maryland) rivers. Lenses were dissected into three layers (surface, middle, core) and analyzed separately to investigate changes over time. We used mixed-effects models to assess differences in isotope ratios among lens layers. Isotope ratios changed from the core to the surface layer and δ 13 C were suggestive of a change from terrestrial to marine sources and δ 15 N showed an increase in trophic level as individuals grew, as would be expected when transitioning from detrital sources to marine prey. However, the isotope ratios of the outer lens layer generally did not correspond with the muscle, perhaps indicating a different temporal interval. These data suggest temporal accretion of lens proteins provide a record to explore sea lamprey ecology.

Maine↗
USGS2017

Assessing the global distribution of river fisheries harvest: A systematic map protocol

Background Although surface freshwater comprises < 0.01% of the total water volume of earth, freshwater inland capture fisheries and aquaculture represent 40% of the global reported finfish harvest. While the social, economic, and ecological importance of inland fish and fisheries is difficult to overstate, they are often undervalued and underappreciated. Accurate information about these highly dispersed fisheries is inherently difficult to acquire, often unreported, and not collected in a standardized format globally. A standardized river fishery database is needed for managing aquatic systems as well as for defining relevant development policies. Here, we describe our methodology to search, identify, and describe available river fisheries information to create a harmonized global database of river fisheries harvest. This database will provide the first global database of spatially and temporally explicit river fisheries data. The database can be used to identify locations, hotspots of data collection, and gaps in existing knowledge and will be especially important to inform studies and management at larger spatial scales (i.e., watershed, regional, or global scales). This database will also be critical for developing fish biomass models for rivers, which can provide managers with information critical for decision-making, such as improved valuation methods for river fish and fisheries. Methods This systematic map protocol describes the methodology to search, identify, and describe available information on river fish and fisheries across the globe. We define river fisheries as “both capture and aquaculture of river finfish species for food, income, or recreation”. River fish species are those finfish that live part, or all of their lives in rivers. The searches will be conducted for the period from 1950 to present using bibliographic databases and grey literature sources. To identify relevant evidence, pre-defined inclusion and exclusion criteria will be used to screen articles at title, abstract, and full text. A searchable database containing extracted meta-data from relevant included studies will be developed and presented as a geodatabase. The final systematic map will consist of a descriptive narrative report of the distribution and content of river fish literature including a geodatabase of available information.

Environmental Evidence↗
USGS2004

History and effects of hatchery salmon in the Pacific

There has been a long history of production of hatchery salmon along the Pacific coast - from California’s first efforts in the 1870s using eggs from chinook and rainbow trout to the recent large-scale production hatcheries for pink salmon in Japan and the Russian Far East. The rationale for this production has also varied from replacement of fish lost in commercial ocean harvests to mitigation and restoration of salmon in areas where extensive habitat alteration has reduced salmonid viability and abundance. Over the years, we have become very successful in producing a certain type of product from salmon hatcheries, but until recently we seldom questioned the impacts the production and release of hatchery fish may have on freshwater and marine aquatic ecosystems and on the sustainability of sympatric wild salmon populations. This paper addresses the history of hatcheries around the Pacific Rim and considers potential negative implications of hatchery-produced salmon through discussions of biological impacts and biodiversity, ecological impacts and competitive displacement, fish and ecosystem health, and genetic impacts of hatchery fish as threats to wild populations of Pacific salmon.

Speaking for the Salmon↗
USGS2011

Verification of a ‘freshwater-type’ life history variant of juvenile American shad in the Columbia River

American shad are native to the Atlantic coast of North America and were successfully introduced to the Pacific coast in the 1870s. They are now more abundant in the Columbia River than are its native salmon. As in their native range, Columbia River American shad are anadromous and have been assumed to solely exhibit an ‘ocean-type’ life history, characterized by a short period of juvenile rearing in freshwater, followed by seaward migration and saltwater entry before age-1, with sexually mature individuals returning to freshwater to spawn beginning at age-3. During October 2007, emigrating juvenile American shad were captured in the juvenile fish monitoring facility at Bonneville Dam (river kilometer 235) on the Columbia River. Their length frequencies revealed the presence of two modes; the lower mode averaged 77 mm fork length (FL) and the upper mode averaged 184 mm FL. A subsample of fish from each mode was aged using otoliths. Otoliths from the lower mode (n=10) had no annuli, indicating that they were all age-0, while otoliths from the upper mode (n=25) had one or two annuli, indicating that they were either age-1 or age-2, respectively. Spawning adults collected in June 2007 averaged 393 mm FL (range 305-460 mm; n=21) and were estimated to range in age from 3-6. Elemental analyses of juvenile and adult otoliths provide evidence for deviations from the typical migration pattern expected for this species, including extensive freshwater rearing of up to two years. This evidence shows that a ‘freshwater-type’ of juvenile American shad exists as year-round or transient residents in the Columbia River basin. The ecological role of this life history variant within the fish community is unknown.

Idaho, Oregon, Washington↗
USGS2020

Fish growth rates and lake sulphate explain variation in mercury levels in ninespine stickleback (Pungitius pungitius) on the Arctic Coastal Plain of Alaska

Mercury concentrations in freshwater food webs are governed by complex biogeochemical and ecological interactions that spatially vary and are often mediated by climate. The Arctic Coastal Plain of Alaska (ACP) is a heterogeneous, lake-rich landscape where variability in mercury accumulation is poorly understood. Earlier research indicated that the level of catchment influence on lakes varied spatially on the ACP, and affected mercury accumulation in lake sediments. This work sought to determine drivers of spatial variation in mercury accumulation in lake food webs on the ACP. Three lakes that were a priori identified as “high catchment influence” (Reindeer Camp region) and three lakes that were a priori identified as “low catchment influence” (Atqasuk region) were sampled, and variability in water chemistry, food web ecology, and mercury accumulation was investigated. Among-lake differences in ninespine stickleback ( Pungitius pungitius ) length-adjusted methylmercury concentrations were significantly explained by sulphate concentration in lake water, a tracer of catchment runoff input. This effect was mediated by fish growth, which had no pattern between regions. Together, lake water sulphate concentration and fish age-at-size (proxy for growth) accounted for nearly all of the among-lake variability in length-adjusted methylmercury concentrations in stickleback (R 2 adj = 0.94, p < 0.01). The percentage of total mercury as methylmercury (a proxy for net Hg methylation) was higher in sediments of more autochthonous, “low catchment influence” lakes ( p < 0.05), and in the periphyton of more allochthonous, “high catchment influence” lakes (p < 0.05). The results indicate that dominant sources of primary production (littoral macrophyte/biofilm vs. pelagic phytoplankton) and food web structure (detrital vs. grazing) are regulated by catchment characteristics on the ACP, and that this ultimately influences the amount of methylmercury in the aquatic food web. These results have important implications for predicting future mercury concentrations in fish in lakes where fish growth rates and catchment inputs may change in response to a changing climate.

Alaska↗
USGS1993

Energy budget for yearling lake trout, Salvelinus namaycush

Components of the energy budget of yearling lake trout ( Salvelinus namacush ) were derived from data gathered in laboratory growth and metabolism studies; values for energy lost as waste were estimated with previously published equations. Because the total caloric value of food consumed by experimental lake trout was significantly different during the two years in which the studies were done, separate annual energy budgets were formulated. The gross conversion efficiency in yearling lake trout fed ad libitum rations of alewives at 10°C was 26.6% to 41%. The distribution of energy with temperature was similar for each component of the energy budget. Highest conversion efficiencies were observed in fish fed less than ad libitum rations; fish fed an amount of food equivalent to about 4% of their body weight at 10°C had a conversion efficiency of 33% to 45.1%. Physiologically useful energy was 76.1–80.1% of the total energy consumed. Estimated growth for age-I and -II lake fish was near that observed for laboratory fish held at lake temperatures and fed reduced rations.

Journal of Freshwater Ecology↗
USGS2025

Relationships between larval fish drift, time of day and discharge in an Ozark stream

We examined the relationship between larval fish numbers and discharge during a high flow event in Bear Creek, Arkansas, a small Ozark stream. Additionally, we examined the relationship between fish numbers and time of day, and the spatial distribution of families and size classes. A total of 3,083 fish from five families were collected. Leuciscidae was the dominant family collected, followed by Percidae, and Catostomidae. Larval fish in Bear Creek were not susceptible to increased discharge from the flood event, as all three families exhibited strong significant negative relationships to discharge at night when discharge began to decline. Larval fish in Bear Creek drifted significantly more at night than during the day, with the exception of large percids, which exhibited no diel pattern. Leuciscidae and small Percidae showed a spatial pattern of distribution across the stream at night, with higher drift densities in near shore nets. The results from our study indicate that fish drift in Bear Creek was an active process, with most larval fish drifting in response to decreased light intensity. We suggest future studies consider the effects of flood intensity on larval fish drift relative to diel periodicity.

Arkansas↗