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At least 343 records · Page 19Linked to original sources
USGS2025

The effect of turbidity on foraging by prerostrum juvenile Paddlefish

Objective A previous study evaluating restoration success of Paddlefish Polyodon spathula suggested that excessive turbidity in lakes and rivers may inhibit foraging by juveniles prior to the development of the rostrum. Although a Paddlefish's rostrum, which contains electroreceptors, helps the fish to locate zooplankton prey, the prerostrum stage lacks many of these electroreceptors, potentially affecting foraging in highly turbid waters. To evaluate this hypothesis, we conducted a series of laboratory experiments in small aquaria by varying the level of turbidity measured as Secchi tube depth: >95 (clear tap water), 40, 20, 10, or 5 cm. Methods For each foraging trial, approximately 300 zooplankton were added to the aquaria, followed by three postlarval Paddlefish, which were allowed to feed on the zooplankton for approximately 18 h. After the 18-h period, Paddlefish were removed and dissected and the zooplankton in the gut were counted to quantify foraging success. Results From three experimental trials, we observed statistically significant nonlinear relationships for two trials, which included the largest fish tested. The smallest Paddlefish size-class showed no significant trend in foraging among turbidity treatments. However, the subsequent trials, which contained larger Paddlefish, both showed unimodal responses, with the highest foraging observed at moderate (30–50-cm Secchi tube depth) turbidity levels. Conclusions High turbidity and excessively clear water both appear to affect foraging by juvenile Paddlefish before the rostrum is fully developed, depending on fish size. Understanding this relationship can further influence management and restoration projects directed at this species.

Transaction of the American Fisheries Society↗
USGS2025

Behavioral responses of Silver Carp to underwater acoustic deterrent sounds

Objective Invasive carps continue to spread across the Mississippi River basin, posing significant ecological risk. Identifying technologies to slow their dispersal is critical. The use of sound has been proposed as a method to modify the behavior of Silver Carp Hypophthalmichthys molitrix , offering a nonstructural deterrent strategy. Methods Silver Carp implanted with acoustic transmitters were released into earthen ponds equipped with telemetry arrays. The fish were exposed to a 30-min playback of three underwater sounds (chirp saw, chirp square, and 100-hp boat motor). Movement trajectories were analyzed using a two-state hidden Markov model to estimate the effects of environmental and experimental variables on fish behavior. Results The results of the hidden Markov model supported two behavioral states. State 1 was characterized by longer step lengths (distance between positions) and greater directional persistence in turning angle (change in direction between two intervals), indicative of heighted activity. State 2 was defined by shorter step lengths and less directional persistence, suggesting reduced activity. Silver Carp that were exposed to the chirp square sound had an increased likelihood of entering state 1, whereas the 100-hp boat motor sound promoted transitions to state 2. Conclusions Underwater sounds distinctly influenced the movement of Silver Carp in earthen ponds. The chirp square sound elicited heightened activity levels, demonstrating potential for use in acoustic deterrent applications. However, the response of Silver Carp to these sounds may be influenced by the size of the study environment or the absence of natural drivers of fish behavior, such as food or reproduction. This study contributes to the development of nonstructural, species-specific deterrent systems by identifying sounds that influence the behavior of invasive carps. The application of sound-based methods may play a critical role in integrated pest management strategies for invasive carps, potentially limiting their spread while minimizing effects on native species.

Transactions of the American Fisheries Society↗
USGS2025

Seasonal movements and demographics of the endangered White River Spinedace to inform restoration and translocation

Objective Translocation is a tool being explored to restart extirpated populations or facilitate new populations of endangered spring-­dependent fish populations. Our objective was to provide information on habitat requirements for endangered White River Spinedace Lepidomeda albivallis during all seasons of the year and the population demographics that are necessary to plan conservation translocations of this species Methods We tagged and released White River Spinedace with passive integrated transponders during four twice-a-year events. Fish were subsequently recaptured or detected on six passive antennas placed throughout the Flag Springs Complex, Nevada. We evaluated movement data to understand seasonal habitat use patterns, used a Barker model to estimate monthly survival rates, adjusted counts to account for capture probability and estimate abundance, and applied reverse-time mark–recapture models to estimate recruitment to 70 mm total length. Results White River Spinedace were more active but used similar habitats during spawning seasons than during nonspawning seasons. Median life expectancy was about 5 months after tagging, and only 1% of adult White River Spinedace survived 3–4 years posttagging. The estimated population size in the Flag Springs Complex during our sampling period (November 2020 to June 2022) was fewer than a thousand White River Spinedace, and this estimate has been steady or slightly increasing. Conclusions Complex spring habitats with water temperatures ranging about 13°C to 21°C that are free from piscivorous fish are appropriate for White River Spinedace. The White River Spinedace population at Flag Springs is small but stable or increasing in size.

Transactions of the American Fisheries Society↗
USGS2025

Field and laboratory evaluations of visible light as a cue for guiding downstream-migrating juvenile Sea Lamprey

Objective We evaluated white light as a potential guidance cue for juvenile Sea Lamprey Petromyzon marinus in a natural setting as well as the effect of water velocity (0.25-, 0.50-, 0.75-, and 1.0-m/s test velocities) on light guidance behavior in a controlled laboratory flume, and characterized emigration timing and movement rates in a small stream (∼10 m wide and 0.7 m deep). Methods Behaviors and rates of downstream movement were monitored using PIT telemetry in both studies. Results In the field study, downstream movement by juveniles released during October 30–November 27 appeared to be cued by precipitation-induced flow events when water temperatures ranged between 4°C and 8°C. Juveniles expressed lateral attraction to a short, bank-mounted linear light array, but the guidance effect was not strong or consistent between bank light locations. Downstream movement rates decreased slightly when juveniles were exposed to the light cue. In the laboratory flume experiment, at water velocities of 0.25 and 0.75 m/s, lamprey were 2.8 and 3.3 times more likely to be detected at antennas along a wall with a linear light array compared with other antennas across the width of the flume. Significant changes in distribution were detected farther upstream in the flume during 0.25- and 0.50-m/s water velocity trials compared with 0.75-m/s trials. Further, the rate of downstream movement through the length of the flume decreased under artificial lighting compared with dark controls under the 0.25- and 0.75-m/s velocity conditions. Conclusions The results suggest lamprey exhibit a behavioral response to the light cue in both lab and field, but water velocity influences how effectively juveniles can respond to light cues.

Massachusetts↗
USGS2025

Tourists or residents? Life history strategies of Rainbow Smelt in Lake Champlain

Objective Rainbow Smelt Osmerus mordax are the most important native prey fish in the coldwater food web of Lake Champlain, but their history in the lake is not well understood. Writers in the 1800s described a nonresident population of smelt that reached sizes greater than 315 mm that was sympatric with a population of individuals that matured at smaller sizes. No studies, however, have investigated mechanisms that cause the dimorphic size structure of Rainbow Smelt in Lake Champlain. Based on our results, larger fish appear to have life history strategy differences from most of the population, which allow them to grow to larger sizes, faster. We proposed three alternative hypotheses to explain the presence of these large Rainbow Smelt in Lake Champlain: (1) anadromous and landlocked Rainbow Smelt may both be present in the lake, (2) all Rainbow Smelt may be landlocked with the two morphotypes resulting from different diet preferences and/or differences in environmental niche occupancy, or (3) the largest Rainbow Smelt are long-lived and therefore had longer time for growth. Methods We tested these hypotheses using otolith microchemistry, diet (stomach content and stable isotope), and age analyses. Our length-at-age analyses showed that age structure was not bimodal, but there are fish present in the lake as large as those in the 1800s. Results Microelemental analysis indicated that Rainbow Smelt in Lake Champlain were landlocked, with no marine signature. Stomach contents of average-sized Rainbow Smelt were exclusively zooplankton and macroinvertebrates, while the larger Rainbow Smelt were primarily piscivorous and had greater δ 15 N values, which suggests a higher trophic position. A combination of hypotheses 2 and 3 most likely explains current population structure. Elevated manganese : magnesium ratios in larger Rainbow Smelt suggest that they may utilize a hypoxic environmental niche, a potential key life history strategy allowing for faster growth, suggesting that there may be intraspecific variation in how Rainbow Smelt use the basins of Lake Champlain. Conclusions Based on our results, larger fish appear to have life history strategy differences from most of the population that allow them to grow to larger sizes, faster. Future studies are needed to uncover the nuances of the mechanisms for growth.

New York, Vermont↗
USGS2025

Cardiac and behavioral responses to chemical and electrical immobilization in Lake Trout

Objective Immobilizing or anesthetizing fish is important for promoting fish welfare in numerous routine activities that involve handling. Electroanesthesia, an alternative to traditional chemical anesthetics, uses weak electrical current to immobilize fish while current is applied, resulting in near-immediate induction and recovery. The physiological effects of electroanesthesia appear to be minimal or comparable to those of chemical anesthetics, but knowledge gaps exist on cardiac responses during treatment and behavioral responses in a controlled setting. Methods Lake Trout Salvelinus namaycush were immobilized by one of four treatments: control (physical restraint); eugenol (AQUI-S 20E); and continuously applied, low-voltage electroanesthesia with either constant DC or transcutaneous electrical nerve stimulation (TENS). We evaluated the heart rate while fish were immobilized, reflexes at 1 h posttreatment, and survival and movements in a laboratory setting over a 6-d posttreatment period. Results The heart rates of fish immobilized with either electroanesthesia treatment (constant DC: mean ± SE = 12.6 ± 1.1 beats/min; TENS: 13.1 ± 1.2 beats/min) were not significantly different from those of control fish (10.0 ± 1.2 beats/min) while immobilized. However, fish immobilized with eugenol exhibited heart rates that were more than three times higher (32.1 ± 1.2 beats/min) than those of control fish while immobilized. Treatments had no effect on reflex scores at 1 h posttreatment, the 6-d survival rate of fish (100%), or movement behavior during the hours (1–24 h) or days (6 d) after treatment. Conclusions This study adds to a growing body of research finding a lack of negative physiological or behavioral responses resulting from continuously applied electroanesthesia, suggesting that it is at least as safe as many chemical anesthetics in this respect. The significant cardiac response of Lake Trout while immobilized with eugenol warrants further investigation. While the body of research on immobilizing agents in fish grows, species-specific data remain sparse, and users would benefit from pilot testing before wider application.

Transactions of the American Fisheries Society↗
USGS2025

Genetic analysis of Missouri’s Topeka Shiners with implications for the propagation of understudied small-bodied freshwater fishes

Objective Best practices for conservation hatcheries to conserve genetic diversity and minimize adaptation to captivity have been established for decades, but how to apply them is not clear in every circumstance. As a growing number of aquatic species are propagated in captive settings, addressing the fit of these practices to each system will help managers operate optimally while conserving hatchery resources. Small-bodied freshwater fish present a unique set of traits compared with species that are typically considered for propagation (i.e., salmonids), including a patchy distribution within a watercourse. We examine the propagation and reintroduction program that supports the Topeka Shiner Miniellus topeka , an endangered minnow in the Midwestern USA. Methods We genotyped shiners from groups with different histories (two reintroduced, three captive, and two remnant populations) at 11 microsatellite loci and compared genetic diversity, genetic structure, effective population size, and evidence of population bottlenecks. We also looked at the breeding structure by genetically assigning hatchery-reared young ( n = 148) to candidate parents. Results We documented high levels of genetic structure among the two natural populations in our study. We also noted lower diversity and evidence of bottlenecks in hatchery-reared groups. However, hatcheries may support sufficient (>50) effective population sizes with minimal space. Conclusions Hatcheries may avoid bottlenecks in other small-bodied freshwater fish by collecting wild fish from a broad area and frequently incorporating them into the captive population. Within the hatchery, we emphasize the need to reduce generational overlap by stocking all production fish and/or subdividing the captive populations.

Missouri↗
USGS2025

Modeling lamprey distribution using flow, geomorphology, and elevation in a terminal lake system

Objective Lampreys are an ecologically important group of fishes. Several species are imperiled and lack key distribution and habitat data. The terminal Goose Lake Basin, U.S.A. is home to two such species, the Goose Lake Lamprey, Entosphenus sp. (formally undescribed), and the Pit-Klamath Brook Lamprey, E. lethophagus . Species distribution models (SDMs) are useful for identifying key habitats; however, SDMs are subject to accuracy impairments caused by scale mismatches and spatial autocorrelation—both exacerbated by the hierarchical structure of dendritic stream networks. Our goal was to relate lamprey presence–absence to ecological drivers and predict the distribution of lampreys across the Goose Lake Basin. Methods Using a dataset pooling approach, we integrated count and presence–absence data from five surveys and relevant habitat variables from publicly available, geospatial datasets to build logistic regression models. To account for potential mismatches of scale, we compared three sample grains for slope and sinuosity (i.e., stream segment lengths: 250, 500, and 1,000 m), and two scales of elevation (site and watershed). We accounted for spatial autocorrelation by incorporating network-based and Euclidean spatial dependencies using a spatial stream network (SSN) modeling approach. Using the best-fit spatial and non-spatial models, we predicted basin-wide lamprey distribution. Result Flow, sinuosity at our largest sample grain (1,000 m), and watershed-scale elevation were positively associated with lamprey presence, whereas slope was negatively associated. The non-spatial model predicted lamprey presence among sinuous, low-gradient streams, whereas the spatial model, which identified Euclidean and flow-connected spatial relationships, predicted contiguous patches with a high probability of occurrence near areas with previously observed presences. Conclusions Our study revealed ecological relationships and produced an accurate basinwide SDM. Prediction and inference improved after accounting for spatial relationships across multiple scales. Developing accurate and efficient modeling strategies that incorporate the hierarchical structure inherent to stream ecosystems aids in the management and conservation of native fishes such as lampreys.

Transactions of the American Fisheries Society↗
USGS2025

Protected from Pterygoplichthys? Predicting thermal habitat suitability for nonnative armored catfish in the Suwannee River

Objective Nonnative fishes can modify ecosystems and harm economies when they are introduced to new environments. Climate change is likely to assist the spread and establishment of some nonnative fishes (e.g., warmwater species), but spatiotemporal gaps in water temperature monitoring and modeling may prevent ecologists and managers from forecasting thermal habitat suitability for these taxa. The purpose of this study was to develop a predictive model of winter water temperatures and thermal habitat suitability for two priority nonnative armored catfish, Vermiculated Sailfin Catfish Pterygoplichthys disjunctivus and Orinoco Sailfin Catfish P. multiradiatus , in the Suwannee River, Florida and Georgia. Methods Precipitation- and groundwater-corrected air–water temperature models were developed and evaluated using a model selection procedure to predict water temperatures at four sites in the Suwannee River. These models were chosen because they blend the simplicity of air–water temperature models with the accuracy of hydrometeorological models to create an efficient, economical, management-relevant approach for analyzing and forecasting water temperature. Results Most of the top-performing water temperature models (92%) had precipitation or groundwater corrections to air–water temperature formulations. Projected mean and maximum water temperatures increased as simulated climate change intensified. All four Suwannee River sites studied were projected to be thermally hospitable to the survival of Vermiculated Sailfin Catfish. Lower river sites, noticeably warmer than upper river sites, were conducive to the survival of Orinoco Sailfin Catfish throughout the winter months. The upper river sites were too cold for Orinoco Sailfin Catfish survival in some climate-change scenarios, but the Suwannee River has an abundance of constant-temperature springs that are likely hospitable to Vermiculated Sailfin Catfish and Orinoco Sailfin Catfish throughout the year. Conclusions The findings suggest that winter water temperatures will likely not be a barrier to the survival of Pterygoplichthys catfish in the Suwannee River, amplifying the importance of conservation and management approaches to inhibit their spread and establishment. If the Pterygoplichthys population remains small and isolated and decision makers are able to devote required staff time and resources to managing these species, removal and eradication at local if not broader scales may be reasonable goals. This study provides a water temperature modeling approach that can aid ecologists and managers in prioritizing sites to prevent the introduction, slow the dispersal, eradicate, and control Pterygoplichthys catfish and other nonnative fishes in the Suwannee River and beyond.

Florida, Georgia↗
USGS2025

Long-term surgery survival, body condition effects, and incision healing of Silver Carp and buffalo species comparing sedation methods across seasons

Objective Internal tagging for telemetry studies requires invasive surgery procedures, necessitating sufficient sedation to support animal welfare. Challenges with existing chemical sedatives have resulted in technological alternatives, including electrosedation, with these newer methods less extensively studied. Our primary objective was to understand long-term survival, body-condition effects, and incision healing after surgical implantation of an imitation telemetry transmitter under three different sedation techniques. Methods We collected Silver Carp Hypophthalmichthys molitrix and buffalo Ictiobus spp. from the Missouri River watershed in 2022 and 2023, during each of the four seasons. One of three sedation techniques was applied: electric fish handling gloves, tricaine methanesulfonate (MS-222), and eugenol. Additionally, we observed a group of fish that were unsedated but subjected to handling similar to that experienced during surgery. Fish were monitored to determine the effects of treatment, individual characteristics, surgery characteristics, and time-varying environmental factors on survival, body condition, and incision healing over 69- to 85-d holding periods. Results Long-term survival was higher for buffalo (86%) than Silver Carp (57%), with the fewest mortalities during the winter trial and most in summer, but sedation treatment did not affect survival. Smaller fish had a greater risk of mortality but better incision healing. Incision healing scores improved in warmer temperatures. Conclusions Difference in seasonal effects on survival and healing indicate a need to consider trade-offs when scheduling tagging for projects. However, a lack of difference in survival among treatments, including the group that was handled but did not undergo surgery, suggests no advantage of one sedative over another, but handling impacts may require more consideration.

Transactions of the American Fishery Society↗
USGS2025

Reevaluation of an adaptive management framework for invasive Grass Carp within Lake Erie

Objective Response efforts to control invasive species frequently require making decisions in the face of substantial uncertainty. Adaptive management, which emphasizes learning during the process of managing, can be useful in cases where uncertainty impedes the decision-making process. Here, we describe how technical and institutional learning led to reformulating decision-making elements, known as double-loop learning, and how uncertainty stemming from a lack of knowledge influenced the selection of alternative strategies in an ongoing adaptive management process for invasive Grass Carp Ctenopharyngodon idella in Lake Erie. Methods When response efforts began, little was known about the population dynamics, ecology, and biology of Grass Carp within the lake. The availability of funding for sustained response efforts was also unknown. A network population model was constructed that relied heavily on values and estimates from limited data to project adult Grass Carp abundance in Lake Erie and evaluate the ability of various response strategies to achieve the desired objectives. After this initial assessment, the collection of new information was emphasized as response efforts increased to aid future assessments. With this expanded knowledge and including additional input from stakeholders, we modified the population model, evaluated new response scenarios, refined objectives, and examined the influence of uncertainty (parameter and expert opinion) on Grass Carp response efforts. Results Under uncertainty of population model parameters and expert opinion, the value-of-information analysis revealed that uncertainties in spawning deterrent efficacy, survival, and the underlying stock–recruitment relationship were important and could change the preferred decision. The efficiency of spawning deterrents influenced the preferred decision outcome among alternative strategies, particularly when >80% of fish were allowed to pass and spawn, indicating that a deterrent may not be worth implementing if passing rates are above this threshold. Conclusions We thereby demonstrate the benefits for invasive species management programs of implementing learning and resolving uncertainties within an adaptive management framework to improve decision making.

Lake Erie↗
USGS2025

Multi-scale habitat characteristics influence Paleback Darter occupancy and detection probability

Objective The limited distribution of the Paleback Darter Etheostoma pallididorsum , which is often associated with dynamic headwater streams, makes the species vulnerable to changes in its environment in west-central Arkansas. A detailed understanding of habitat characteristics that support the species at multiple spatial scales is limited. This project assessed the relative influences of local- and broadscale habitat characteristics on Paleback Darter occupancy and detection probability. Methods Backpack electrofishing was performed, and a mix of in situ and remote habitat characteristics was linked to the Paleback Darter data. A single-season occupancy model was used to examine factors influencing Paleback Darter occupancy. Candidate models were ranked using Akaike's information criterion corrected for small sample sizes. Results A total of 158 Paleback Darters were collected at 13 sites during 35 of the 150 surveys. Paleback Darter occupancy and detection probability were estimated to be 0.26 (95% CI = 0.16–0.40) and 0.90 (95% CI = 0.75–0.96), respectively. Distance from springs was negatively related to Paleback Darter occupancy. Conclusions Springs appear to be a key in the Paleback Darter's life history strategy, and spring preservation is likely vital to the species’ conservation.

Transactions of the American Fisheries Society↗
USGS2025

Impacts of lake elevation decline on spawning habitat of a critical, native forage species

Objective Lake elevation decline is a global phenomenon with pronounced effects in arid regions that changes the characteristics of nearshore habitat area available to lacustrine spawners, potentially impacting recruitment and whole-lake food web dynamics. Our objective was to understand the potential effects of lake elevation decline on spawning habitat for the Tui Chub Siphateles bicolor , a lacustrine spawner and critical component of the native food web in Pyramid Lake, Nevada. Methods We explored the distribution of ripe Tui Chub in nearshore habitat by associating habitat characteristics to ripe Tui Chub CPUE from a custom gill-net configuration, with data analyzed using generalized linear mixed-effects models. We then explored potential spawning habitat availability at all potential lake elevations using an elevation-explicit model of the basin that we developed based on several bathymetric and geospatial data sets and the knowledge of spawner distribution gained in the first component of the study. Results Ripe Tui Chub catch was primarily predicted by temperature, reaching a maximum between 14.2°C and 24.8°C found at less than 15 m of depth in Pyramid Lake throughout the summer spawning period. We estimated that with a contemporary decline in lake elevation of 8 m, Pyramid Lake will host the minimum area of spawning habitat based on morphometry alone at a 40% decrease from a theoretical maximum. Conclusions A decrease in lake elevation or an increase in lake temperatures—both of which are probable events based on future climate scenarios and estimates of water extraction upstream of Pyramid Lake—is likely to further restrict Tui Chub spawning habitat area. Our results have important implications for ecological water demand in Pyramid Lake and provide managers with information facilitating a science-based approach to managing the fish community.

Nevada↗
USGS2025

Fish composition in a complex freshwater estuary: Environmental DNA metabarcoding versus capture surveys

Objective The potential for environmental DNA (eDNA) to disperse widely from source organisms enables high detection efficiency but raises questions about eDNA's ability to differentiate fine-scale spatial patterns relative to conventional fish capture data. Methods We evaluate these questions in the St. Louis River estuary—a hydrologically and spatially complex coastal system within Lake Superior that supports a diverse assemblage of resident and migratory fish species—via comparison of eDNA metabarcoding (12S and 16S loci) to multigear capture survey data from 2 years and two seasons. Results The eDNA and capture surveys collectively yielded 68 fish species: 2 species detected only by capture, 27 detected only by eDNA, and 39 shared across both survey types but having generally higher occurrence frequencies with eDNA than capture. Six species detected only by eDNA were unexpected, having no prior records in the Lake Superior basin. Data from paired eDNA and capture stations showed little relationship between the two survey types, with capture yielding species at stations that eDNA did not, eDNA detecting species in different habitats and distant locations from any captures, and assemblage patterns homogenized in eDNA surveys relative to capture surveys. Conclusions Our study finds that eDNA is a sensitive tool for assessing species presence at the system scale but that capture surveys may better yield the fine-scale spatial distribution information of interest to fisheries and habitat managers, especially in spatially and hydrologically complex systems.

Transactions of the American Fisheries Society↗
USGS2025

Electric field-induced detachment and vibration analysis for Sea Lamprey

Objective: Sea lamprey Petromyzon marinus , a known ecological threat to native fish populations in the Great Lakes, use their oral suction disc to navigate challenging environments when moving upstream to spawn. This study investigated the physiological response of adult sea lamprey to detach under pulsed direct current electric fields. Methods: Adult sea lampreys in an attaching position were exposed to pulsed direct current electric fields at four different field strengths (0.7, 1.1, 1.3, and 1.9 V/cm). Behavioral responses, including detachment and vibration, were observed and analyzed. Fast Fourier Transform analysis was applied to vibration data to quantify the frequency of vibration exhibited by non-detached sea lamprey. Statistical correlations between detachment rates and vibration responses to sea lamprey sex, weight, and length were evaluated to determine influencing factors. Results: The highest detachment rate (91%) was observed at 1.1 V/cm, with the detachment rate above 70% for other field strengths. Fast Fourier Transform analysis revealed that the vibration frequencies closely matched the signal while stronger fields elicited a more pronounced vibration amplitude without significantly increasing detachment. Non-detached sea lampreys exhibited “twitching” behavior synchronized with the electric field frequency. Sex, weight, and length had minimal influence on detachment rates and vibration responses. Conclusion: This study provided insights into the behavioral responses of sea lamprey under electric fields, highlighting the potential for optimizing electric deterrents for selective control. While not all sea lampreys detach during electroshocking, understanding their behavior can be crucial in maximizing detachment rates and contributing to improved management strategies for this invasive species.

Transactions of the American Fisheries Society↗
USGS2025

Riverscape genetics of nonnative Brook Trout to inform native cutthroat trout conservation

Objective Understanding how riverscape features influence gene flow is critical for managing population connectivity in freshwater species. We examined how landscape and stream characteristics shape the spatial genetic structure of nonnative Brook Trout Salvelinus fontinalis in a headwater stream network proposed for reintroduction of federally threatened Greenback Cutthroat Trout Oncorhynchus virginalis stomias . Brook Trout were studied to evaluate the suitability of this habitat for supporting a native trout metapopulation. Methods We genotyped 757 Brook Trout from 22 sites across a 60-km stream network using 12 microsatellite loci. Spatial genetic structure was assessed using clustering analysis (program STRUCTURE) and pairwise differentiation metrics ( F ST and Jost’s D ). A spatial network modeling approach was used to quantify the effects of riverscape features (e.g., stream gradient, stream order, waterfalls, and flow direction) on trout gene flow. Results Genetic clustering identified four distinct tributary groups, while estimates of pairwise genetic differentiation indicated some genetic connectivity across the network (mean F ST = 0.04; mean Jost’s D = 0.06). Trout gene flow was impeded by waterfalls, steep stream gradients, and increased hydrologic distance. Higher stream order and downstream flow direction were associated with stronger gene flow, and stream segments containing waterfalls and steeper gradients showed greater asymmetries between upstream and downstream gene flow. Conclusions Brook Trout populations in this stream network are spatially structured, but gene flow persists and is mediated by physical riverscape features and hydrologic distance. The observed patterns of genetic connectivity suggest that this habitat can support connectivity among populations of reintroduced Greenback Cutthroat Trout. In future native trout reintroduction efforts, prioritizing habitats with gradual stream gradients and fewer waterfalls would promote population connectivity.

Transactions of the American Fisheries Society↗
USGS2026

Longitudinal variability of demographics and life history in an anadromous spawning population within a large, unimpeded East Coast, USA, watershed

Objective The goal of this study was to characterize the variability in age, growth, and life history of sea-run fish throughout a large, East Coast, USA, watershed to improve the parameterization of longitudinal variation in demographics and spawning histories in an undammed river. Methods Both live and dead American Shad Alosa sapidissima were collected during spring 2020 and 2021. Sex, length, age, and repeat spawning information were recorded for all individuals ( n = 512). Growth curves were created to test hypotheses about the variables that were related to the growth rates of American Shad for this relatively unsampled portion of the spawning population in the Delaware River. Results We observed variation in size, age, repeat spawning probability and propensity, and sex ratios from downstream to upstream as well as during the spawning season. Individual traits also varied among the fish that died during migration and those that were collected alive. Conclusions This study expands the current knowledge about variability in the life history traits that are commonly used in assessing and managing an anadromous fish that spawns upstream in a large, undammed watershed. Our results have broad implications for the assessment and management of anadromous fish populations globally and contribute to understanding parity along a continuum. Some potential priorities for future work include using telemetry to understand the final disposition of live fish, investigating fine-scale genetic control for correlated life-history traits, and investigating the correlations between natal origin (i.e., genetic stock mixing) and longitudinal variation within spawning populations.

New York, Pennsylvania↗
USGS2026

A multi-species, multi-season evaluation of body condition effects on fish survival in a coolwater stream

Objective Body condition is often used as a surrogate of individual fitness in fisheries ecology and management, but empirical data demonstrating this linkage are few. Here, we investigated whether weight at length (i.e., body condition) explained individual variation in survival. Methods We conducted a mark–recapture survey of three native fishes subseasonally (every 2 months) over 28 months in a coolwater Piedmont stream in South Carolina, United States. We used a Cormack–Jolly–Seber model in the Bayesian state–space framework to characterize whether survival was explained by body condition. Results Body condition changed subseasonally, with its peak in spring (May) and trough in fall (November) in all three species (Bluehead Chub Nocomis leptocephalus , Creek Chub Semotilus atromaculatus , and Mottled Sculpin Cottus bairdii ). Survival decreased in warmer subseasons for all species. Additionally, individuals with higher body condition survived better than those with lower condition only in these warmer subseasons and only in the Mottled Sculpin, a species that is territorial and the most intolerant of warmer temperatures among the study species. Conclusions Our findings show that body condition is a predictor of survival only when populations undergo high mortalities in some but not all species, which are likely caused by a combination of factors, such as physiological stress, diminished food resources, and increased competition for resources.

South Carolina↗