Smallmouth Bass Micropterus Dolomieu Research Articles

Smallmouth Bass and Walleye predation on stocked age‐0 Walleye in Lake Oahe, South Dakota

AbstractObjectiveWalleye Sander vitreus are important sport fish that are commonly stocked to supplement populations. Increases in Smallmouth Bass Micropterus dolomieu abundance have prompted concerns regarding potential predation by these and other piscivores on stocked Walleye. Our objectives were to assess the timing and duration of predation on stocked Walleye, the frequency of occurrence and percent composition of Walleye in predator diets, and the percentage of stocked Walleye consumed.MethodsWe collected Smallmouth Bass, adult Walleye, Largemouth Bass M. nigricans, and Northern Pike Esox lucius diets in May (prestocking) and June–September (poststocking) 2019 and 2021 from three bays in Lake Oahe, South Dakota. We stocked two bays with Walleye (30–32 mm; 255–1649 Walleye/ha), whereas one bay was unstocked and served as a reference. We estimated Smallmouth Bass population abundance using Schnabel capture–recapture models, and we used bioenergetics to estimate the percentage of stocked age‐0 Walleye consumed.ResultWe found age‐0 Walleye in up to 11.4% of Smallmouth Bass diets and 14.6% of adult Walleye diets during the poststocking period. A single Largemouth Bass consumed one Walleye at 3 days poststocking (DPS), whereas we did not identify Walleye in Northern Pike diets. Daily mean percent composition by weight (±95% confidence interval) of age‐0 Walleye in diets peaked at 43.2 ± 35.1% at 3 DPS for Smallmouth Bass and 49.8 ± 97.7% at 14 DPS for adult Walleye. Following the peaks, age‐0 Walleye percent composition by weight rapidly declined and was generally 0% after 25 DPS. Smallmouth Bass abundance was 0.4–5.6 fish/ha, whereas recaptures of other predator species were insufficient for reliable population estimates. We estimated that Smallmouth Bass consumed 29,930 age‐0 Walleye in 2019 and 12,535 age‐0 Walleye in 2021 (up to 14.7 ± 4.7% of stocked fish), potentially representing an important source of stocking mortality.ConclusionOur research provides insights into the effects of poststocking predation on age‐0 Walleye by Smallmouth Bass and, to a lesser extent, Walleye, Largemouth Bass, and Northern Pike. Managers should consider predation on stocked fingerling Walleye from resident predators and should contemplate alternative stocking locations or timing to reduce potential predation.

Sport fish movement responses to a littoral zone coarse woody habitat addition

AbstractObjectiveFish movements and distributions throughout an ecosystem are important for understanding ecological interactions, conservation, and management. Coarse woody habitat (CWH) additions are a popular habitat enhancement tool that can influence movements and distributions of fishes; however, behavioral responses in relation to CWH additions are understudied. The objectives of our study were to test for changes in habitat use and behavioral responses of Muskellunge Esox masquinongy, Smallmouth Bass Micropterus dolomieu, and Walleye Sander vitreus to CWH additions in a small inland northern lake over 3 years and to evaluate two common forms of fish tracking to estimate daily movement of these fishes.MethodsWe used passive integrated transponder tag data collected continuously at 10 littoral sites and radiotelemetry data collected biweekly during the summer–fall months prior (2017) and following (2018–2019) CWH addition to examine movement behaviors and estimate daily probability of movement for the three species among lake habitats using multistate models.ResultWalleye were the most likely to remain near CWH, followed by Smallmouth Bass and Muskellunge. All species were more likely to move away from the modified and unmodified littoral zones and were more likely to remain in the offshore zone. Increased movement of fish may be in response to CWH creating a refuge for forage fish and subsequent increases in prey search times.ConclusionOur results suggest that CWH additions may alter established species‐specific annual movements, distributions, and habitat use to differing degrees in ecosystems, as our results differ from other CWH studies. Methodologically, radio‐tagging was most effective for offshore tracking but most labor intensive. Novel passive integrated transponder arrays (less labor intensive once installed) worked well to monitor movement between habitat types in shallow littoral areas. Long‐term monitoring of behavioral changes will be essential to assessing the stability changes caused by these habitat alterations.

Effects of poor recruitment on riverine Smallmouth Bass population dynamics

AbstractObjectiveAltered flow regimes pose significant risks to the stability of populations of riverine Smallmouth Bass Micropterus dolomieu. Periods of poor recruitment, due to early life stage mortality resulting from high‐flow events, can cause size‐structure and density alterations of populations. The aim of this study was to opportunistically test for changes in dynamic rates of a riverine Smallmouth Bass population using a long‐term data set that spanned a period of poor recruitment.MethodsOur study evaluated size‐specific CPUE (fish/h), mortality, growth, and condition and tested for recruitment determinants of Smallmouth Bass through three consecutive years of poor age‐0 recruitment in the South Branch Potomac River, West Virginia. We used fall nighttime boat electrofishing surveys during 2009–2022 to monitor this population before and after the poor‐recruitment time frame (2016–2018).ResultAge‐0 CPUE was greater during the time frame prior to the poor‐recruitment time frame. However, there was no difference in the CPUE of quality‐length Smallmouth Bass between the two time frames and CPUE of preferred‐length fish was greater during the poor‐recruitment time frame. Growth and relative weight increased during the poor‐recruitment time frame. There was no significant difference detected in mortality between the recruitment time frames. Streamflow during the spawning period was a significant factor influencing fall recruitment of age‐0 Smallmouth Bass. A Ricker density‐dependent model with an added streamflow term performed as well as a basic, log‐linear streamflow model and a density‐independent model that also incorporated a streamflow term.ConclusionOur results provide evidence of density‐dependent structuring in this population. Decreases in population density increased population dynamic rates that maintained or improved size structure. High adult biomasses did not increase age‐0 recruitment. Many riverine Smallmouth Bass populations may display favorable density‐dependent responses to declines in juvenile recruitment. Thus, management agencies should better understand the resiliency of these populations prior to establishing expensive programs or regulations, which may be ineffective, to combat alterations in juvenile recruitment.

Mark–recapture surveys affect nest site fidelity but not reproductive timing of male Smallmouth Bass

AbstractObjectiveFish population surveys in north‐temperate lakes are often conducted in the fall or spring when individuals are easy to capture with traditional fisheries techniques. Because some fishes are preparing to spawn or are spawning during these seasons, there is a critical need to better understand the potential influences of these surveys on decisions that are related to fish reproduction.MethodsWe tested whether spring mark–recapture surveys using fyke nets followed by electrofishing affect the reproductive behaviors of male Smallmouth Bass Micropterus dolomieu in a northern Wisconsin lake. Fyke netting, electrofishing, and whole‐lake nest snorkeling surveys were conducted during 2001–2008, and Floy‐tagged males were tracked across years to test whether capture in the fyke nets only or capture in the electrofishing survey influenced interyear nest site fidelity and reproductive timing.ResultThe mark–recapture surveys were conducted preceding the spawning of Smallmouth Bass, and returning males that were caught in the electrofishing survey nested ~50 m farther from their prior year's nest than both males that were captured only in fyke nets and males that were captured by neither method. Average interyear nest distances were ~200 m, and median interyear nest distances were ~90 m for males that were not captured in the electrofishing survey. Electrofishing and fyke netting did not influence the timing of reproduction.ConclusionSpring electrofishing surveys for Smallmouth Bass have the potential to displace breeding males from preferred nesting habitats. If displacement negatively influences fitness (i.e., age‐0 survivorship to maturation), spring electrofishing surveys would not be recommended for assessing Smallmouth Bass populations. However, spring population surveys often occur soon after ice off, and surveys that are conducted at these colder temperatures are typically less stressful and less likely to result in mortality. Future research should test for fitness implications of reduced nest site fidelity following electrofishing in Smallmouth Bass while considering potential fitness trade‐offs if surveys are moved later in the year.

Male guarding behavior and brood predators of invasive Bluegill in a Japanese lake

AbstractObjectiveThe Bluegill Lepomis macrochirus, which utilizes colony spawning, has been introduced globally, and in Japan it is considered one of the worst invasive species. However, a detailed examination of the factors driving male guarding behavior and brood predation in the invaded habitat is lacking. The removal of guarding males, a common management technique in Japan, is thought to be effective in controlling Bluegill. However, the colony spawning strategy may influence the effectiveness of selective male removal through brood protection from neighbor males.MethodsBluegill spawning was studied in Lake Nojiri, Nagano, Japan, using underwater video recording and experimental removal of guarding males.ResultBluegill were found spawning in shallow habitat during June–July, and nests were constructed in loosely aggregated colonies, with many solitary nests. Males utilized a variety of guarding behaviors, such as rim circling and predator chases, as well as paternal investment behaviors, such as tail fanning. Males that preyed upon their own eggs defended their nests less aggressively and invested less time in nourishing behaviors. Removal of guarding males revealed that brood predators were primarily conspecific Bluegill, but other fishes, such as invasive Smallmouth Bass Micropterus dolomieu and Largemouth Bass M. nigricans as well as native Japanese Dace Pseudaspius hakonensis, preyed on broods.ConclusionIn concurrence with the colony spawning theory, nests that were located closer to other nests with active guarding males experienced decreased brood predation and increased predator arrival time after male removal. In addition, nests where males had been guarding more aggressively prior to removal experienced reduced brood predation after male removal. These results provide insights into the factors driving male guarding behavior and brood predation of colony‐spawning Bluegill in an invasive habitat and indicate that the removal of guarding males—a common management strategy in Japan—may have reduced effectiveness due to colony spawning.

Long‐term patterns of fish community structure and decline in native species in a Colorado River reservoir, Arizona and Nevada

AbstractObjectiveThe Colorado River has undergone substantial anthropogenic modifications, and a suite of nonnative species have been introduced since the 1800s; consequently, native fish communities are severely imperiled. We examined temporal patterns in fish community structure in Lake Mohave (i.e., lower Colorado River basin) over 40 years from 1980 to 2020.MethodsWe examined long‐term abundance and richness trends and the trajectory of fish community structure in multivariate space to assess stability and turnover using results from biannual (spring and autumn) trammel‐net monitoring over 40 years from 1980 to 2020.ResultNonnative fishes were established prior to sampling, precluding the ability to determine historical fish community structure. Bonytail Gila elegans and Razorback Sucker Xyrauchen texanus were the only two remaining native fishes, and both declined precipitously in abundance through time. However, a repatriation program initiated in 1991 prevented Razorback Sucker from extirpation, while reintroduction efforts for Bonytail have failed. Both wild populations are gone. Total catch per unit effort showed a negative relationship from 1980 to 2020, whereas total species richness showed no relationship. Long‐term abundance trends at the species level indicated three nonnative species (i.e., Gizzard Shad Dorosoma cepedianum, Yellow Bullhead Ameiurus natalis, and Smallmouth Bass Micropterus dolomieu) increased, nine decreased, and three showed no relationship. Fish community composition exhibited low stability and moderate turnover and shifted directionally through time in multivariate space, with the formation of three clusters, possibly indicating alternative states.ConclusionThe contemporary fish community shows little resemblance to the endemic ichthyofauna that has historically occupied the Colorado River, and the Razorback Sucker is the only remaining native species due to recovery efforts. Continued adaptive management will be required to preserve the most genetically diverse Razorback Sucker population in the Colorado River system, especially while coexisting with an unstable nonnative fish community.

Annual recruitment is correlated with reproductive success in a smallmouth bass population

Annual recruitment in fish is undoubtedly impacted by a vast number of biotic and abiotic factors. That is especially the case for fish species such as the black bass (species in the genus Micropterus), where there is extended parental care. Although much focus has been given in the past on determining the roles that many of these factors (e.g., temperatures, wind, flow rates, and habitat change) play in determining recruitment among the back basses, little attention has been given to assessing what role reproductive success plays in that determination. To address this question, we conducted a long-term study on two adjacent smallmouth bass (SMB) Micropterus dolomieu Lacepède, 1802 populations in eastern ON to assess the relationship between annual fry cohort size (FCS) (i.e., population-wide reproductive success) and annual recruitment. To measure population-wide annual FCS, we used snorkel surveys to conduct a complete census of nesting SMB males during the spawn from 1990 to 2015. During those surveys, we quantified mating success, determined which nests were successful or not, and calculated the number of independent fry produced each year by summing those numbers across all successful nests. Summer snorkel surveys from 1991 to 2016 assessed annual recruitment through visual counts of age 1+ juveniles. Results demonstrated a highly significant, positive, linear relationship between annual FCS and annual recruitment.

Assembling the Right Pieces: Developing an Interdisciplinary Team to Study Disease, Decline, and Recovery of a World‐Class Smallmouth Bass Fishery

Managing and understanding fisheries dynamics are becoming more complex as new and seemingly more complicated environmental factors are identified. Often management requires resources beyond that of any one entity and calls for collaboration among partners with differing priorities and backgrounds to account for the complexity of factors influencing fisheries. We present a collaborative case study from the Susquehanna River basin, Pennsylvania, where Smallmouth Bass Micropterus dolomieu have faced population declines, mortality events, and notable signs of disease in recent years. Collaboration was required to study many facets of the fishery and the environment simultaneously to better understand risk factors and underlying relationships influencing Smallmouth Bass health. The outcomes from this interdisciplinary collaboration allowed for identification of contributing risk factors, led to the development of products and analytical techniques that were mutually beneficial to all partners involved, and provided knowledge that was integrated into fish health and fisheries management.

A multi-level assessment of biological effects associated with mercury concentrations in smallmouth bass, Micropterus dolomieu

Total mercury (THg) was measured in muscle (fillet) and liver tissue of adult smallmouth bass Micropterus dolomieu collected at multiple sites in the Potomac and Susquehanna River drainages within the Chesapeake Bay watershed. Smallmouth bass in these drainages have experienced episodic mortality events, a high prevalence of skin lesions and reproductive endocrine disruption (intersex or testicular oocytes and plasma vitellogenin in males). A multi-level assessment of general and reproductive health including indicators at the organismal, organ, cellular and molecular levels was conducted on adult smallmouth bass during the spring (prespawn) season. Concentrations of THg were correlated with increased visible abnormalities, increased macrophage aggregates and tissue parasite burdens. In male bass positive correlations of THg were observed with plasma vitellogenin and hepatic transcript abundance of estrogen receptor β1 and androgen receptor α, while there was a negative association with estrogen receptors α and β2 and androgen receptors β. In female bass there was a negative correlation between THg and plasma vitellogenin as well as hepatic transcript abundance of vitellogenin, choriogenin, estrogen receptor β2 and 17β hydroxysteroid dehydrogenase. Associations of THg concentrations with various biological indicators suggest mercury may be an important environmental stressor contributing to the observed adverse effects in smallmouth bass populations.

A comprehensive multi-state conditional occupancy model for evaluating interactions of non-native and native species

A major challenge in ecology is disentangling interactions of non-native, potentially invasive species on native species. Conditional two-species occupancy models examine the effects of dominant species (e.g., non-native) on subordinate species (e.g., native) while considering the possibility that occupancy of one species may affect occupancy and/ or detection of the other. Although conditional two-species models are useful for evaluating the influence of one species on presence of another, it is possible that species interactions are density dependent. Therefore, we developed a novel two-species occupancy model that incorporates multiple abundance states (i.e., absent, present, abundant) of the native species. We showcase the utility of this model with a case study that incorporates random effects and covariates on both occupancy and detection to help disentangle species interactions given varying occupancy and detection in different abundance states. We use snorkel survey data from the Umpqua basin, Oregon, where it is hypothesized that smallmouth bass Micropterus dolomieu, a non-native piscivore, exclude Umpqua chub Oregonichthys kalawatseti, a small endemic minnow. From our two-species multi-state (2SMS) model, we concluded that average occupancy was low for both fishes, and that when non-native bass were present, overall native chub occupancy in the present (0.18 ± 0.05 SD) and abundant (0.19 ± 0.03) states was higher than when non-natives were absent (0.14 ± 0.02/ 0.08 ± 0.02), indicating the non-native was not excluding the native species. By incorporating a species interaction factor, we found a positive association (6.75 ± 5.54 SD) between native chub and non-native bass. The covariates strongly related to occupancy were elevation, algae, and land cover type (urban and shrub). Detection probability for both species (0.21–0.82) was most strongly related to the covariates day of year, water temperature, gravel substrate, and stream order/ magnitude. Incorporation of detection probability and covariates enabled interpretation of interactions between the two species that may have been missed without their inclusion in the modeling process. Our new 2SMS occupancy model can be used by scientists and managers with a broad range of survey and covariate data to disentangle species interactions problems to help them inform management decisions.

Are smallmouth bass more mobile in large lakes than once thought?

Smallmouth bass Micropterus dolomieu are generally considered to be a sedentary species. Previous tagging studies in lentic systems have found low annual movements based on fishery-dependent tag returns or limited detections from electronic transmitters, though occasional long-distance movements have been observed (i.e., >30 km). In this study, we implanted 23 smallmouth bass sampled from a recreational tournament in Lake Erie with acoustic transmitters and monitored their movements for two years (September 2018–September 2020) using a large-scale array of passive acoustic receivers. We documented 42 percent (8/19) of the at-large fish making long-distance movements throughout Lake Erie; these fish moved an average distance of 109.9 ± 26.6 km (mean ± SE; ranging 3.5–355.1 km) per year. Importantly, six of eight fish crossed jurisdictional boundaries (five into Ontario waters and one into Michigan waters). One individual moved a total of 505.3 km over the two years, the furthest distance an individual smallmouth bass has been documented moving across the literature. While observed movements may have been initially biased due to tournament displacement and capture method, tagged fish continued to make long-distance movements in the second-year post-release. Previous movement studies may have underestimated smallmouth bass movement scope in large, lentic systems due to low spatial and temporal coverage of recapture effort (including receiver coverage) relative to system size. Our results suggest that some smallmouth bass can make consistent long-distance movements in large systems like the Laurentian Great Lakes, indicating this species’ spatial ecology remains understudied in large lentic systems.

COVID-19 reduced recreational fishing effort during the black bass spawning season, resulting in increases in black bass reproductive success and annual recruitment

In Opinicon Lake, Ontario during two non-pandemic years (2019 and 2022) the hook-wounding rates from recreational angling observed among nesting male largemouth bass Micropterus salmoides (LMB), and nesting male smallmouth bass Micropterus dolomieu (SMB), were quite high, but typical of those observed in the lake over the last 20 years of monitoring. That level of illegal, preseason angling resulted in very low percentages of both LMB and SMB nesting males being successful at raising their broods to independence, rates comparable to those observed for this lake in previous years. In 2020 and 2021, amid the COVID-19 pandemic, however, access to fishing in Ontario was severely limited during the bass spawning season, which serendipitously provided a natural “whole-lake bass spawning sanctuary” to study. Not surprisingly, the hook-wounding rates for nesting male LMB and SMB in Opinicon Lake were the lowest rates ever observed over the last 30 + years. Concomitantly, the percentage of nesting male LMB and SMB that were successful at raising their broods to independence was approximately 3–4 times greater than that in the non-COVID years. Not unexpectedly, those increases in nesting success translated to similar increases in LMB and SMB reproductive success (production of post parental care, independent fry). More importantly, those increases further resulted in large increases in the annual recruitment of both LMB and SMB. This unanticipated COVID-driven experiment revealed that using bass spawning sanctuaries would be more efficient than closed seasons as a management strategy to conserve levels of black bass annual recruitment.

Estimating Recycling of Fish in Catch‐and‐Release Fisheries

The prevalence of catch‐and‐release angling for many species has increased over the past several decades. A potential benefit of catch‐and‐release fisheries is higher catches for anglers due to multiple captures of individual fish within a season. We term the measure of this benefit “recycling rate,” defined as the total catch in a fishing season divided by the number of individuals caught at least once. Multiple‐capture studies are common in the literature, but our recycling rate is a new metric that could be helpful in evaluating recreational fisheries. Estimates of recycling rate will be dependent on several factors, especially the distribution of angling selectivities among individual fish, which is generally unknown. We compared several models that estimated recycling rate based on different assumptions about angling selectivity. Application of the models to Smallmouth Bass Micropterus dolomieu data from Lake Mille Lacs, Minnesota, demonstrated that estimates of recycling rate were robust to assumptions about the distribution of angling selectivity.

Fish and Zooplankton Community Responses to the Cessation of Long-Term Invasive Eurasian Watermilfoil (Myriophyllum spicatum) Chemical Treatments in a North-Temperate, USA Lake

2,4-Dichlorophenoxyacetic acid (2,4-D) is commonly used to control invasive aquatic macrophytes, including Eurasian watermilfoil (Myriophyllum spicatum) (EWM). Potential influences of 2,4-D on non-target organisms are poorly understood; however, research has suggested the possibility of lethal effects on certain fish species. Lake Ellwood, Wisconsin was treated with 2,4-D to control EWM annually during 2003–2012. Fish surveys following treatment revealed natural recruitment failures of several regionally thriving species, including largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus). We hypothesized that these species had been negatively influenced by the chemical treatments. We monitored the post-chemical treatment fish community and aquatic ecosystem for responses during 2013–2019. Similar data were collected from Cosgrove (EWM absent) and Seidel lakes (EWM present, no chemical treatment) as reference systems. Limnological and submersed aquatic vegetation conditions did not change on Lake Ellwood post-chemical treatment. Total zooplankton density increased immediately post-chemical treatment on Lake Ellwood and then stabilized, whereas total zooplankton density did not change on the reference lakes over time. Analyses indicated immediate increases in recruitment post-chemical treatment for largemouth bass, smallmouth bass (Micropterus dolomieu), bluegill, and yellow perch (Perca flavescens). Back calculation of year class strength confirmed failures occurred during treatment for northern pike (Esox lucius), largemouth bass, bluegill, and black crappie (Pomoxis nigromaculatus). Our results provide evidence to suggest long-term 2,4-D treatments may negatively influence fish through lethal and sublethal mechanisms. Thus, there remains a critical need for directed research on whole-lake herbicide treatment side-effects.

The Importance of Phenology and Thermal Exposure to Early Life History Success of Nonnative Smallmouth Bass in the Yellowstone River

AbstractKnowledge of potential spread by introduced species is critical to effective management and conservation. The Smallmouth Bass Micropterus dolomieu is an example of a fish that has been introduced globally, often spreads after introduction, and has substantial predatory impacts on fish assemblages. Nonnative Smallmouth Bass in the free‐flowing Yellowstone River, Montana, have expanded from warmer, downstream sections of river into colder, upstream sections containing socio‐economically valuable trout fisheries. We sought insight into mechanisms controlling upstream spread by evaluating whether progressively colder upstream climates physiologically constrained successful recruitment by limiting age‐0 growth and preventing overwinter survival (i.e., population establishment). We documented the phenology, growth, and overwinter survival of age‐0 Smallmouth Bass across a temperature gradient leading to their upstream extent in the Yellowstone River. The upstream extent of population establishment did not appear limited by water temperature alone. Age‐0 body size at the onset of winter did not differ significantly between colder, upstream reaches and warmer, downstream reaches. Instead, the earlier hatch timing exhibited by some age‐0 individuals in upstream sections allowed them to experience longer growing seasons than many individuals in downstream sections. This counter‐intuitive hatching phenology mediated much of the expected decreases in growth in colder, upstream climates. Furthermore, evidence of successful overwinter survival and simulations of age‐0 starvation mortality indicated that age‐0 individuals at the upstream extent of their distribution successfully recruited to the age‐1 year‐class during four consecutive years. However, age‐0 individuals were rare or absent throughout the uppermost upstream distribution of adults, suggesting that something other than temperature limits or discourages reproduction farther upstream. Taken together, our results suggest that Smallmouth Bass have not yet reached the thermal limit of their upstream distribution in the Yellowstone River and that future spread may challenge fisheries managers tasked with management of coldwater trout fisheries in this river.

Movement and habitat use by smallmouth bass Micropterus dolomieu velox in a dynamic Ozark Highlands riverscape.

Stream fish movement in response to changing resource availability and habitat needs is important for fish growth, survival and reproduction. The authors used radio telemetry to evaluate individual movements, daily movement rates, home ranges and habitat-use characteristics of adult (278-464 mm LT ) Neosho smallmouth bass Micropterus dolomieu velox in three Ozark Highlands streams from June 2016 to February 2018. The authors quantified variation in movement and habitat use among seasons and streams and examined relations with select environmental cues (i.e., temperature and discharge), fish size and sex. Maximum movement distances were an order of magnitude greater in the larger Elk River (17.0 km) and Buffalo Creek (12.9 km) than in the smaller Sycamore Creek (1.71 km), were similar in both upstream and downstream directions and typically occurred during the spring. Most movement rates were ≤10 m day-1 in all streams and seasons, except for Elk River during spring. Ranking of linear mixed-effects models using AICc supported that movement rates were much greater in spring and increased with stream size. Spring movement rate increased with discharge and water temperature; only weak relationships were apparent during other seasons. Increased variation in water temperature had a small negative effect on movement rate. Home range size was highly variable among individuals, ranging 45-15,061 m (median: 773 m), and was not related to fish size, sex, season or stream. Although some fish moved between rivers, this study's tagged fish did not use reservoir or associated interface habitat. Water temperatures used by this study's tagged fish followed seasonal patterns but indicated the use of thermal refugia during summer and winter. Deeper-water habitats were used in Buffalo Creek and in winter across all study streams, whereas greater velocities used in the Elk River likely reflect the increased use of run habitats. Use of pool habitats predominated among tagged fish, particularly in smaller streams. The results of this study indicate considerable heterogeneity in movement and habitat use within and among lotic populations of Neosho smallmouth bass. These findings suggest that population-specific management may be appropriate and highlight the importance of natural flow conditions (i.e., spring high flows) and connected habitats for this endemic sport fish, particularly in smaller streams.

Temporal Trends in Macroscopic Indicators of Fish Health in the South Branch Potomac River

AbstractOver recent decades, the South Branch Potomac River, West Virginia, has experienced fish kills and episodes of suppressed health in adult fish that have spanned small stretches to nearly 120 km of contiguous habitat. Although factors such as endocrine disruption, chemical contaminants, and infectious agents have been detected, no single causal mechanism has been identified. To gain information about the temporal nature of abnormalities, differences in life stage impacts, and potential risk factors, investigations of rank scores of macroscopic fish health indicators were conducted utilizing seasonal and annual boat electrofishing surveys for Smallmouth Bass Micropterus dolomieu (SMB) and Golden Redhorse Moxostoma erythrurum (GDR). Gill and body abnormalities were assigned rank scores for each fish based on visual severity and were tested for correlation with seasonal climatic (flow and stream temperature) and environmental (stream pH, dissolved oxygen, and turbidity) factors. Comparisons between juveniles and adults for these species indicated that body lesions were more common for adult GDR and gill lesions were more common for adult SMB. Significantly higher rank sums of adult gill abnormalities corresponded with heavy annual mortality of SMB between ages 2 and 3 (86%), the period during which this species transitions from juvenile to adult length. Higher ranks were frequently assigned to fish of both species for gill and body/fin lesions in summer and fall samples. Low stream discharge and lower pH correlated with elevations of body raised lesions (GDR) and body erosions (GDR and SMB) as well as erosions of the gill lamellae (SMB). This study connects the disciplines of fisheries management, fish health, and environmental monitoring, providing information gained through tracking the macroscopic conditions of these two indicator species to focus future studies and better understand risks to fish health.

Critical Thermal Maximum Values for Stream Fishes, Including Distinct Populations of Smallmouth Bass

AbstractUnderstanding the thermal tolerances of stream fishes, including sport fishes, is important for assessing thermal stressors that are common across the landscape. Our study objectives were to determine the thermal tolerances of 17 stream fishes (15 species and 2 genetically distinct populations of juvenile Smallmouth Bass Micropterus dolomieu: the Neosho subspecies M. dolomieu velox and the Ouachita strain M. sp. cf. dolomieu velox). Fish were collected from the field and acclimated to laboratory conditions at 20°C or 25°C, with dissolved oxygen maintained above 6 mg/L. We determined the critical thermal maximum (CTM) using an incomplete block design with 9–11 replications for each species. During trials, we increased the water temperature at a rate of 2°C per hour until fish experienced loss of equilibrium. The estimated CTM ranged from 32.43°C to 38.26°C among species. The CTM values differed significantly between taxonomic groups and species, including the genetically distinct populations of Smallmouth Bass. The Neosho subspecies of Smallmouth Bass had a significantly lower thermal tolerance than the Ouachita strain at both acclimation temperatures; however, the magnitude of the difference was about 0.5°C greater at the higher acclimation temperature. Closely related species, including the Bigeye Shiner Notropis boops and Kiamichi Shiner N. ortenburgeri, had significantly different thermal tolerances despite occupying similar riverine locations. Our results suggest that our perceptions of a species’ thermal tolerance based on that of closely related species or that of species using similar habitat may be incorrect. Moreover, the differences in thermal tolerances among populations may be an important consideration for conservation and management actions, such as stocking decisions. Laboratory data such as those provided in this study can be integrated with field data to better assess thermal responses of fishes in a changing environment.

Rapid population decline in one of the last recruiting populations of the endangered Clanwilliam sandfish (Labeo seeberi): The roles of climate change and non‐native fish

Abstract Freshwater fish are in decline worldwide as a result of introduced non‐native species, impoundment, water quality changes, over‐abstraction, and climate change. The Clanwilliam sandfish Labeo seeberi is an endangered migratory cyprinid endemic to a single river system in South Africa's Cape Fold Ecoregion. It has declined across its range and persists as fragmented populations in the Doring River system. One of the last recruiting populations occurs in the Oorlogskloof River, where three non‐native fish species are present: smallmouth bass Micropterus dolomieu, bluegill sunfish Lepomis macrochirus (both alien and invasive), and banded tilapia Tilapia sparrmanii (extralimital). Impacts of these non‐natives, together with climate change, may pose a serious threat to this important sandfish population and to other cohabiting native fish species. A 6 year data set, collected over 9 years and spanning 25 km of the Oorlogskloof River, was analysed to characterize spatio‐temporal variation in sandfish abundance and size structure and to evaluate the relative impacts of biotic and abiotic factors on population trends. Sandfish experienced a 92.6% decline in relative abundance from 2013 to 2018, driven by a 99.6% decline in young‐of‐the‐year individuals. A combination of extreme rainfall events and drought appear to have played a key role in the decline and subsequently prevented recovery. Small sandfish (≤200 mm) were almost entirely absent from the centrarchid‐invaded section of the Oorlogskloof but were relatively abundant where these centrarchids were absent, suggesting a strong adverse impact of these non‐native species. Banded tilapia co‐occurred with sandfish without any apparent adverse impacts on the relative abundance or size structure of sandfish. Improved water resource management and preventing the further spread of non‐natives must be conservation priorities. Localized eradication of non‐native species must also be considered to reclaim habitat and restore connectivity. Translocations may be required to prevent species extinctions.

The determining factor of radiocesium contamination levels in smallmouth bass Micropterus dolomieu in Lake Hayama after the Fukushima fallout

The determining factor of radiocesium contamination levels in smallmouth bass Micropterus dolomieu in Lake Hayama after the Fukushima fallout