Smallmouth Bass Research Articles

Genomic divergence, local adaptation, and complex demographic history may inform management of a popular sportfish species complex.

The Neosho Bass (Micropterus velox), a former subspecies of the keystone top‐predator and globally popular Smallmouth Bass (M. dolomieu), is endemic and narrowly restricted to small, clear streams of the Arkansas River Basin in the Central Interior Highlands (CIH) ecoregion, USA. Previous studies have detected some morphological, genetic, and genomic differentiation between the Neosho and Smallmouth Basses; however, the extent of neutral and adaptive divergence and patterns of intraspecific diversity are poorly understood. Furthermore, lineage diversification has likely been impacted by gene flow in some Neosho populations, which may be due to a combination of natural biogeographic processes and anthropogenic introductions. We assessed: (1) lineage divergence, (2) local directional selection (adaptive divergence), and (3) demographic history among Smallmouth Bass populations in the CIH using population genomic analyses of 50,828 single‐nucleotide polymorphisms (SNPs) obtained through ddRAD‐seq. Neosho and Smallmouth Bass formed monophyletic clades with 100% bootstrap support. We identified two major lineages within each species. We discovered six Neosho Bass populations (two nonadmixed and four admixed) and three nonadmixed Smallmouth Bass populations. We detected 29 SNPs putatively under directional selection in the Neosho range, suggesting populations may be locally adapted. Two populations were admixed via recent asymmetric secondary contact, perhaps after anthropogenic introduction. Two other populations were likely admixed via combinations of ancient and recent processes. These species comprise independently evolving lineages, some having experienced historical and natural admixture. These results may be critical for management of Neosho Bass as a distinct species and may aid in the conservation of other species with complex biogeographic histories.

Decision support for aquatic restoration based on species-specific responses to disturbance.

Disturbances to aquatic habitats are not uniformly distributed within the Great Lakes and acute effects can be strongest in nearshore areas where both landscape and within lake effects can have strong influence. Furthermore, different fish species respond to disturbances in different ways. A means to identify and evaluate locations and extent of disturbances that affect fish is needed throughout the Great Lakes. We used partial Canonical Correspondence Analysis to separate “natural” effects on nearshore assemblages from disturbance effects. Species‐specific quadratic models of fish abundance as functions of in‐lake disturbance or watershed‐derived disturbance were developed separately for each of 35 species and lakewide predictions mapped for Lake Erie. Most responses were unimodal and more species decreased in abundance with increasing watershed disturbance than increased. However, eight species increased in abundance with current in‐lake disturbance conditions. Optimum Yellow Perch (Perca flavescens) abundance occurred at in‐lake disturbance values less than the gradient mean, but decreased continuously from minimum watershed disturbance to higher values. Bands of optimum in‐lake conditions occurred throughout the eastern and western portions of the Lake Erie nearshore zone; some areas were less disturbed than desirable. However, watershed‐derived disturbance conditions were generally poor for Yellow Perch throughout the lake. In contrast, optimum Smallmouth Bass (Micropterus dolomieu) abundance occurred at in‐lake disturbance values greater than the gradient mean and continuously increased with increasing watershed disturbance. Smallmouth Bass responses to disturbance indicated that most of the nearshore zone was less disturbed than is desirable and were most abundant in areas that the Yellow Perch response indicated were highly disturbed. Mapping counts of species response models that agreed on the disturbance level in each spatial unit of the nearshore zone showed a fine‐scale mosaic of areas in which habitat restoration may benefit many or few species. This tool may assist managers in prioritizing conservation and restoration efforts and evaluating environmental conditions that may be improved.

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.

Indicators of fish population responses to avian predation with focus on double-crested cormorants

Double-crested cormorants (Nannopterum auritum) have been implicated as causes of fish population declines in many locations across their breeding range. Two challenges facing managers are identifying fisheries population metrics indicative of cormorant impacts and determining when this evidence becomes actionable. Building upon existing studies, we conducted a meta-analysis of eight data-rich systems across the Laurentian Great Lakes region of the United States for common fish population responses to changes in cormorant abundance. Specifically, we examined trends in mean total female length at age-3 (TL3), female mean length and age at 50 % maturity, and mean age evenness as indicated by Shannon’s Equitability Index. Annual observations for these metrics were independently regressed linearly against cormorant density by system for walleye (Sander vitreus), yellow perch (Perca flavescens), smallmouth bass (Micropterus dolomieu), and northern pike (Esox lucius) populations. TL3 was the most sensitive with 9 of the 14 datasets statistically significant (r2 range 0.29 to 0.86). Maturity metrics were moderately sensitive to trends in cormorant predation with mean total length at 50 % maturity significant in 4 out of 11 datasets (r2 range 0.27–0.41) and mean age at 50 % maturity significant in 3 out of 11 datasets (r2 range 0.12 – 0.51). Least sensitive was age evenness with the Shannon Index significant in 3 out of 12 datasets (r2 typically < 0.25). Of metrics tested, TL3 was the most reliable indicator of changes in cormorant effects despite varying system changes and management responses among locations.

Bioaccumulation and trophic magnification of emerging and legacy per- and polyfluoroalkyl substances (PFAS) in a St. Lawrence River food web

Research on per- and polyfluoroalkyl substances (PFAS) in freshwater ecosystems has focused primarily on legacy compounds and little is still known on the presence of emerging PFAS. Here, we investigated the occurrence of 60 anionic, zwitterionic, and cationic PFAS in a food web of the St. Lawrence River (Quebec, Canada) near a major metropolitan area. Water, sediments, aquatic vegetation, invertebrates, and 14 fish species were targeted for analysis. Levels of perfluorobutanoic acid (PFBA) in river water exceeded those of perfluorooctanoic acid (PFOA) or perfluorooctane sulfonate (PFOS), and a zwitterionic betaine was observed for the first time in the St. Lawrence River. The highest mean PFAS concentrations were observed for the benthopelagic top predator Smallmouth bass (Micropterus dolomieu, Σ60PFAS ∼ 92 ± 34 ng/g wet weight whole-body) and the lowest for aquatic plants (0.52–2.3 ng/g). Up to 33 PFAS were detected in biotic samples, with frequent occurrences of emerging PFAS such as perfluorobutane sulfonamide (FBSA) and perfluoroethyl cyclohexane sulfonate (PFECHS), while targeted ether-PFAS all remained undetected. PFOS and long-chain perfluorocarboxylates (C10–C13 PFCAs) dominated the contamination profiles in biota except for insects where PFBA was predominant. Gammarids, molluscs, and insects also had frequent detections of PFOA and fluorotelomer sulfonates, an important distinction with fish and presumably due to different metabolism. Based on bioaccumulation factors >5000 and trophic magnification factors >1, long-chain (C10–C13) PFCAs, PFOS, perfluorodecane sulfonate, and perfluorooctane sulfonamide qualified as very bioaccumulative and biomagnifying. Newly monitored PFAS such as FBSA and PFECHS were biomagnified but moderately bioaccumulative, while PFOA was biodiluted.

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.

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

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

Seventy years of food-web change in South Bay, Lake Huron

Though aquatic ecosystems (and the Laurentian Great Lakes in particular) have faced many stressors over the past century, including fisheries collapses and species invasions, rarely are data available to evaluate the long-term impacts of these stressors on food web structure. Stable isotopes of fish scales from the 1940s to the 2010s in South Bay, Lake Huron were used to quantify trophic position and resource utilization for fishes from offshore (alewife, cisco, lake trout, lake whitefish, rainbow smelt) and nearshore (rock bass, smallmouth bass, white sucker, yellow perch) habitats, providing one of the longest continuous characterizations of food webs in the Laurentian Great Lakes. Mean δ15N and δ13C values for each species were compared across twenty-year time periods. Using directional statistics, no significant community-wide changes were detected between time periods from 1947 to 1999. In contrast, a significant change was detected between 1980-1999 and 2000–2017, with all species showing increased reliance on nearshore resources. The increase in nearshore resource reliance for lake whitefish between these time periods was the greatest in magnitude compared with any other species between any two adjacent time periods. Besides lake whitefish, the increased reliance on nearshore resources was more pronounced for nearshore compared to offshore species. The timing of these shifts coincided with the invasion of dreissenid mussels and round goby, and declines in offshore productivity and prey densities. These results show the unprecedented magnitude of recent food-web change in Lake Huron after 50 years of relative stability.

Effect of wind speed and light intensity on reflex impairment of angled Smallmouth Bass (Micropterus dolomieu)

AbstractWe quantified effects of wind speed and sunlight on Smallmouth Bass (Micropterus dolomieu), a popular gamefish in North America, after catch‐and‐release (C&amp;R) (n = 90) during August for various periods (0, 10, 30 and 90 s) in direct sunlight or shaded from direct sunlight. We evaluated change in skin temperature and reflex action mortality predictor (RAMP) scores. Changes in skin temperature were larger with increasing wind speeds and air exposure duration. Light intensity had no effect on skin temperature or RAMP. Generally, skin temperature decreased (i.e. colder) when wind speed exceeded ~5 km/h and increased (i.e. warmer) when wind speed was below ~5 km/h. Significantly, lower RAMP scores were associated with longer air exposure. Generally, Smallmouth Bass exposed to air for longer than 10 s were significantly more impaired prior to release. We recommend anglers reduce the time that large fish are exposed to air to reduce immediate reflex impairment.

Water Storage Decisions and Consumptive Use May Constrain Ecosystem Management under Severe Sustained Drought

AbstractDrought has impacted the Colorado River basin for the past 20 years and is predicted to continue. In response, decisions about how much water should be stored in large reservoirs and how much water can be consumptively used will be necessary. These decisions have the potential to limit riverine ecosystem management options through the effect water‐supply decisions have on reservoir elevations. We used projected hydrology and river temperatures to compare the outcome of combinations of water storage scenarios and consumptive use limits on metrics associated with ecosystem management of the Colorado River in Grand Canyon. Ecosystem management metrics included the ability to implement designer flows, temperature suitability for fishes, and fragmentation. We compared current water management operations to prioritizing storage in either Lake Mead or Lake Powell combined with three levels of consumptive use. Projected reservoir levels limited environmental flow delivery and increased fragmentation regardless of where water was stored if consumptive use was not limited. Warmer river temperatures associated with low reservoir levels are likely, creating suitable conditions for non‐native species of concern, such as smallmouth bass. Water storage decisions provided variability and management flexibility, but water storage was less important when less water was available, highlighting the importance of keeping water in the system to provide flexibility for achieving ecosystem goals.

Phylogenomics and species delimitation of the economically important Black Basses (Micropterus)

Informed management and conservation efforts are vital to sustainable recreational fishing and biodiversity conservation. Because the taxonomic rank of species is important in conservation and management strategies, success of these efforts depends on accurate species delimitation. The Black Basses (Micropterus) are an iconic lineage of freshwater fishes that include some of the world’s most popular species for recreational fishing and world's most invasive species. Despite their popularity, previous studies to delimit species and lineages in Micropterus suffer from insufficient geographic coverage and uninformative molecular markers. Our phylogenomic analyses of ddRAD data result in the delimitation of 19 species of Micropterus, which includes 14 described species, the undescribed but well-known Altamaha, Bartram’s, and Choctaw basses, and two additional undescribed species currently classified as Smallmouth Bass (M. dolomieu). We provide a revised delimitation of species in the Largemouth Bass complex that necessitates a change in scientific nomenclature: Micropterus salmoides is retained for the Florida Bass and Micropterus nigricans is elevated from synonymy for the Largemouth Bass. The new understanding of diversity, distribution, and systematics of Black Basses will serve as important basis for the management and conservation of this charismatic and economically important clade of fishes.

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.

Short-term behavioural impacts of air-exposure in three species of recreationally angled freshwater fish

Fish captured and released by recreational anglers are often exposed to air to enable hook removal and for admiration (e.g., photography). It is necessary to identify thresholds for air exposure that minimize sublethal alterations to inform best practice guidelines yet doing so in ecological-relevant field settings is challenging. We developed a novel attachment method for tri-axial accelerometer and depth biologgers to quantify short-term post-release behaviour in recreationally angled northern pike (Esox lucius), smallmouth bass (Micropterus dolomieu), and walleye (Sander vitreus) following a range of air exposure treatments (i.e., 0, 15, 30, 60, and 180 s). The biologgers were attached to the fish using a quick-release Velcro® harnesses that facilitated easy retrieval of the device from free-swimming fish without the need to recapture the individual. For this study, biologgers were retrieved after a 10 min observational period. Overall dynamic body acceleration (ODBA) was calculated from accelerometric data to estimate post-release swimming activity. Clustering of ODBA via k-means was used to classify distinct movement patterns: resting, steady-state swimming, and high intensity swimming occurrences. In northern pike, ODBA in the first minute after release was significantly higher in the 0 s air exposure treatment compared to the 15 s, 30 s, 60 s, and 180 s treatments, however the same patterns were not observed for smallmouth bass or walleye. We did not observe differences in the time spent resting, time spent steady-state swimming, or the number of high intensity swimming occurrences among air exposure treatments across all study species. This proof-of-concept study demonstrated the utility of this non-invasive bio-logger approach for the short-term study of catch-and-release and also revealed that for the species and context (e.g., water temperatures of 17–25 º C) studied here, air exposure had relatively little negative short-term impact on behaviour or reflex impairment. Nonetheless, we encourage air exposure to be minimized as longer fight times or higher water temperatures may interact with air exposure to increase behaviour impairments and negatively impact survival.

Gonadal Development in Smallmouth Bass (Micropterus Dolomieu) Reared in the Absence and Presence of 17-α-Ethinylestradiol.

Testicular oocytes in wild adult bass (Micropterus spp.) are considered a potential indication of exposure to estrogenic compounds in municipal, agricultural, or industrial wastewater. However, our ability to interpret links between testicular oocyte occurrence in wild fish species and environmental pollutants is limited by our understanding of normal and abnormal gonadal development. We previously reported low-to-moderate testicular oocyte prevalence (7%-38%) among adult male bass collected from Minnesota waters with no known sources of estrogenic compounds. In the present study, two experiments were conducted in which smallmouth bass (Micropterus dolomieu) fry were exposed to control water or 17-α-ethinylestradiol (EE2) during gonadal differentiation, then reared in clean water for an additional period. Histological samples were evaluated at several time points during the exposure and grow-out periods, and the sequence and timing of gonadal development in the presence of estrogen were compared with that of control fish. Testicular oocytes were not observed in any control or EE2-exposed fish. Among groups exposed to 1.2 or 5.1 ng/L EE2 in Experiment 1 or 3.0 ng/L EE2 in Experiment 2, ovaries were observed in 100% of fish up to 90 days after exposure ceased, and approximately half of those ovaries had abnormal characteristics, suggesting that they likely developed in sex-reversed males. Groups exposed to 0.1, 0.4, or 1.0 ng/L in Experiment 2 developed histologically normal ovaries and testes in proportions not significantly different from 1:1. These findings suggest that, while presumably able to cause sex reversal, juvenile exposure to EE2 may not be a unique cause of testicular oocytes in wild bass, although the long-term outcomes of exposure are unknown. Environ Toxicol Chem 2022;41:1416-1428. © 2022 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Spawning season and nest guarding behavior of invasive smallmouth bass (Micropterus dolomieu) in a Japanese Lake

AbstractSpawning of invasive smallmouth bass (Micropterus dolomieu) was studied in 2020 and 2021, in Lake Nojiri, Nagano, Japan. Male smallmouth bass began nest construction once water temperatures reached 14°C, and eggs progressed to fry dispersal in approximately 2 weeks. The main spawning season was in late May through early June, with a smaller second peak of nests in late June through early July. Nests were constructed primarily under dock cover, and nest size and depth were positively correlated with male body size. Of the nests that received eggs, nearly all progressed successfully to fry dispersal. Time lapse videos of male guarding behavior revealed that as nests progressed, males rotated less and were suspended off the bottom substrate. Similarly, the presence of egg predators was determined by experimental removal of guarding males. Freshwater gobies (Rhinogobius kurodai) were the only egg predators observed and arrived on all nests in the egg stage. However, only a handful of gobies visited each nest, the total number of eggs predated was low, and eggs or alevins in the progressed stage were rarely predated. These results indicate that in Lake Nojiri, smallmouth bass spawning is highly successful and egg predators appear to have minimal effect on egg survival. The stable smallmouth bass fishery without stocking at this lake is likely a product of these favorable spawning conditions. The lack of native egg predators may also be a driving factor in the continued spread of smallmouth bass throughout Japan.

Stage‐specific abiotic and biotic associations of the imperilled Silver ShinerNotropis photogenisin an urban drainage

AbstractStage‐specific abiotic and biotic associations are often poorly described for imperilled freshwater fishes, including Silver Shiner (Notropis photogenis; Threatened), which may limit species protection and recovery efforts. Here, we used fish and habitat sampling data from an urban drainage in southern Ontario, Canada to quantify abiotic and biotic associations for juvenile and adult Silver Shiner, while considering the potential effects of imperfect detection on sampled fishes. Detection probability of Silver Shiner was high (&gt;0.80) across life‐stages, but occupancy models for adults and juveniles included different covariates. The top‐selected occupancy model (lowest Akaike's Information Criterion [AICc]) for adults included a positive effect of site depth, whereas sampling year was included in the top‐selected occupancy model for juveniles. A redundancy analysis suggested unique stage‐specific biotic associations; a positive association was observed between the abundance of adult Silver Shiner and Rosyface Shiner (Notropis rubellus), whereas positive associations were observed between juvenile Silver Shiner and the abundance of Fathead Minnow (Pimephales promelas) and Smallmouth Bass (Micropterus dolomieu). Overall, the results of this study advance the knowledge of stage‐specific abiotic and biotic associations of Silver Shiner, and the probability of species detection, which will inform future monitoring and protection of the species in Canada. More broadly, continued efforts are needed to quantify early life‐stage habitat requirements for informing the recovery of imperilled freshwater species.

Influence of hook barbs on the “through-the-gill” hook removal method for deeply hooked Smallmouth Bass

Sustainable catch-and-release fisheries are based on the assumption that most fish survive an angling event. The adoption of best practices has become important to help mitigate post-release injury, behavioral impairment and mortality. However, in any catch-and-release fishery, a proportion of fish will become inadvertently deeply hooked (e.g., in the gullet) and numerous studies have shown this to be a major driver of mortality. Although available science suggests that cutting the line tends to yield better outcomes than removing hooks in the gullet, there has been interest within the angling community with removing hooks using the “through-the-gill” method where the hook shaft is turned outwards into the gill region and then the hook is removed by pulling anteriorly by gripping the outside bend of the hook. Here, we tested the efficacy of removing barbed and barbless hooks though the gill opening from experimentally deep-hooked Smallmouth Bass (Micropterus dolomieu) relative to leaving the hooks in place. Using a control group and four experimental treatment groups (barbed and removed through the gills; barbless and removed through gills; barbed and left in; barbless and left in), we evaluated handling time, presence of bleeding, incidence of gill or esophageal injury, reflex impairment, incidence of hook shedding (for the left in treatment groups), and survival across a 24-hour monitoring period. Collectively, our results suggested that when hooks were barbed and removed through the gills, fish condition and survival were lower. In addition, barbed hooks were more likely to cause bleeding, gill damage, esophageal tearing, and impair reflexes. When hook removal was done through the gills, the chances of all sublethal outcomes across all categories were more likely to occur. While short-term mortality was not statistically linked with any treatment group, the greatest percentage of mortality (24%) occurred for fish that had barbed hooks removed using the through-the-gill method. These data suggest that when anglers use barbed hooks and encounter a deeply hooked fish, cutting the line poses the least risk to the fish.

Factors Related to Crappie Indices of Abundance in a Large, Fluctuating Canyon Reservoir in Idaho

Crappie (Pomoxis spp.) populations are challenging to manage due to highly variable year-class strength; however, such variability has rarely been investigated in western North America, where crappie often occupy large, steep-sided reservoirs prone to severe drawdown. We investigated the influence that various factors had on crappie abundance, as indexed by long-term trawling for larval fish and long-term electrofishing for older fish. Our primary findings were that: 1) autumn age-0 crappie abundance was higher in years when larval abundance and reservoir flow were higher in the summer; 2) spring age-1 crappie abundance was higher in years when fish were larger and more abundant entering their first winter, when hydraulic residence time was reduced and the reservoir volume was higher during the winter, and when predatory-sized smallmouth bass (Micropterus dolomieu) were more abundant in the spring (though the latter relationship was likely not causative but rather a parallel response to mutually advantageous environmental conditions in the reservoir); and 3) age-0 crappie entering their first winter were larger in years with lower summer larval crappie abundance and warmer summer water temperature. We recommend autumn electrofishing to monitor crappie populations in large canyon reservoirs, where shorelines are often too steep to sample fish with trap nets, because it provides an index of age-0 crappie abundance and size at the onset of their first winter as well as data on older crappie year classes and sympatric species; it also requires less sampling effort than summer trawling.

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.