Robust Redhorse Research Articles

Survival and Contaminants in Imperiled and Common Riverine Fishes Assessed with an In Situ Bioassay Approach

An in situ bioassay approach was used to determine whether aquatic contaminant stressors in a large Atlantic river ecosystem affect the survival of 3 fish species: the largemouth bass (Micropterus salmoides, juveniles), the fathead minnow (Pimephales promelas, adults), and the robust redhorse (Moxostoma robustum, juveniles). Hatchery-propagated fish were placed into cages to assess site-specific survival in the Yadkin-Pee Dee River of North Carolina and South Carolina, USA. Contaminants were measured in caged fish and sediment and surface water at each site. No apparent longitudinal trends in fish survival were detected, and contaminant concentrations varied among sites. Juvenile largemouth bass and robust redhorse did not survive past 13 and 23 d, with corresponding Kaplan-Meier median survival estimates of 9.7 and 12.1 d, respectively. Survival of adult fathead minnows deployed in cages alongside the juvenile fish averaged 43% at the end of the 28-d exposure, with a 22-d median survival estimate. The intersex condition, an indicator of endocrine disruption, was not observed in any adult fathead minnow. Contaminant accumulation in surviving fathead minnows was apparent, with highest accumulated concentrations of polychlorinated biphenyls (34.6-93.4 ng/g dry wt), organochlorine pesticides (19.9-66.1 ng/g dry wt), and mercury (0.17-0.63 μg/g dry wt). Contaminants and other water quality stressors in this river system appear to detrimentally impact juvenile fish survival, with presumed effects at the fish assemblage and community levels. Environ Toxicol Chem 2021;40:2206-2219. © 2021 SETAC.

Trophodynamics of Per- and Polyfluoroalkyl Substances in the Food Web of a Large Atlantic Slope River.

Per- and polyfluoroalkyl substances (PFASs) have attracted scientific and regulatory attention due to their persistence, bioaccumulative potential, toxicity, and global distribution. We determined the accumulation and trophic transfer of 14 PFASs (5 short-chain and 9 long-chain) within the food web of the Yadkin-Pee Dee River of North Carolina and South Carolina, US. Food web components and pathways were determined by stable isotope analyses of producers, consumers, and organic matter. Analyses of water, sediment, organic matter, and aquatic biota revealed that PFASs were prevalent in all food web compartments. Biofilm, an aggregation of bacteria, fungi, algae, and protozoans and a basal resource for the aquatic food web, showed high PFAS accumulation (in 10 of 14 compounds), particularly for perfluorooctanoic acid, with the greatest mean concentration of 463.73 ng/g. The food web compartment with the most detections and greatest concentrations of PFASs was aquatic insects; all 14 PFASs were detected in individual aquatic insect samples (range of <limit of detection [<LOD] to 1670.10 ng/g of wet weight [WW]). These findings may suggest a trophic link between biofilm PFASs and aquatic insect PFASs. Individual fish tissue samples ranged from <LOD to 797.00 ng/g of WW, where perfluorooctanesulfonate (PFOS) was the dominant PFAS among all samples (64%). The ova of an imperiled fish, the robust redhorse (Moxostoma robustum), had concentrations of 10 PFASs (range of <LOD to 482.88 ng/g of WW) and the highest PFOS concentration (482.88 ng/g of WW), indicating a likely maternal transfer. The trophic magnification factors (TMFs) calculated in this study showed that various taxa accumulated PFAS compounds differently. PFBS, a short-chain PFAS compound that would presumably exhibit lesser TMFs, had nine values among our compartments and organisms >1.0 (range of 0.57 to 2.33); it is possible that an unmeasured PFBS precursor may be accumulating in biota and metabolizing to PFBS, leading to a higher than expected TMFs for this compound. Our findings demonstrate the prevalence of PFASs in a freshwater food web with potential implications for ecological and human health.

Intraspecific differences in morphology correspond to differential spawning habitat use in two riverine catostomid species

Maintaining intraspecific diversity is an important goal for fisheries conservation and recovery actions. While ecomorphological studies have demonstrated intraspecific diversity related to feeding or flow regime, there has been little assessment of such variation in regard to spawning habitat. We evaluated the relationship between individual morphology of Robust Redhorse and Notchlip Redhorse and variables describing the spawning habitat from which they were captured, such as current velocity, depth, and substrate particle size. Robust Redhorse (n = 58) and Notchlip Redhorse (n = 43) were captured from spawning aggregations in the lower Savannah River, South Carolina-Georgia using prepositioned grid electrofishers. They were then measured and photographed before being released. We constructed a truss network using digitized landmarks on each of the photographs. Relationships between the morphological and environmental datasets were assessed using canonical correlation analysis. In both species, these morphological predictors were correlated primarily to depth, though current velocity also contributed to the environmental canonical score for Robust Redhorse. Robust Redhorse captured from the deeper locations with higher current velocities had heads with lower aspect ratio compared to individuals captured from shallower areas. Notchlip Redhorse from shallower areas were deeper-bodied and had shorter trunks than counterparts from deeper areas. These differences suggest that ensuring spawning habitat heterogeneity may be an important component to conserving intraspecific diversity, particularly in systems where such habitat is limiting.

Food web contaminant dynamics of a large Atlantic Slope river: Implications for common and imperiled species

Persistent and bioaccumulative contaminants often reach concentrations that threaten aquatic life by causing alterations in organism behavior and development, disruption of biological processes, reproductive abnormalities, and mortality. The objectives of this research were to determine the aquatic food web structure and trophic transfer and accumulation of contaminants within a riverine ecosystem and identify potential stressors to the health of an imperiled fish, the robust redhorse (Moxostoma robustum) and other species of conservation concern in a large Atlantic Slope (USA) river. Trophic position was determined for food web taxa by stable isotope analyses of representative producers, consumers, and organic matter of the Yadkin-Pee Dee River of North Carolina and South Carolina. Contaminant analyses were performed on water, sediment, organic matter, and aquatic biota to assess the prevalence and accumulation of polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), current use pesticides (CUPs), polycyclic aromatic hydrocarbons (PAHs), and selected metals. Contaminants were prevalent in the environment and food web components of the river. PCBs were detected in 32% of biotic samples (mean 0.24μg/g dry weight [DW], range 0.01–3.33μg/g DW), and DDTs (legacy OCPs and metabolites) were detected in 90% (mean 0.014μg/g DW, range 0.0004–0.29μg/g DW). The trace metals manganese and cadmium exceeded published threshold effect concentrations in sediment (460 and 0.99μg/g DW, respectively). Mercury was detected in all food web samples exhibiting a mean of 0.61μg/g DW and range 0.006–2.35μg/g DW (mean 0.13μg/g wet weight [WW], range 0.001–0.6μg/g WW). Concentrations exceeded the 0.2μg/g WW aquatic life criterion for mercury in 38% of fish samples. Fish trophic magnification factors (TMFs; range 0.33–3.75) indicated that contaminant accumulation occurred from both water and dietary sources. The combination of analytical approaches applied here provides new insight into contaminant dynamics with conservation implications.

Effects of Regulated River Flows on Habitat Suitability for the Robust Redhorse

AbstractThe Robust Redhorse Moxostoma robustum is a rare and imperiled fish, with wild populations occurring in three drainages from North Carolina to Georgia. Hydroelectric dams have altered the species' habitat and restricted its range. An augmented minimum‐flow regime that will affect Robust Redhorse habitat was recently prescribed for Blewett Falls Dam, a hydroelectric facility on the Pee Dee River, North Carolina. Our objective was to quantify suitable spawning and nonspawning habitat under current and proposed minimum‐flow regimes. We implanted radio transmitters into 27 adult Robust Redhorses and relocated the fish from spring 2008 to summer 2009, and we described habitat at 15 spawning capture locations. Nonspawning habitat consisted of deep, slow‐moving pools (mean depth = 2.3 m; mean velocity = 0.23 m/s), bedrock and sand substrates, and boulders or coarse woody debris as cover. Spawning habitat was characterized as shallower, faster‐moving water (mean depth = 0.84 m; mean velocity = 0.61 m/s) with gravel and cobble as substrates and boulders as cover associated with shoals. Telemetry relocations revealed two behavioral subgroups: a resident subgroup (linear range [mean ± SE] = 7.9 ± 3.7 river kilometers [rkm]) that remained near spawning areas in the Piedmont region throughout the year; and a migratory subgroup (linear range = 64.3 ± 8.4 rkm) that migrated extensively downstream into the Coastal Plain region. Spawning and nonspawning habitat suitability indices were developed based on field microhabitat measurements and were applied to model suitable available habitat (weighted usable area) for current and proposed augmented minimum flows. Suitable habitat (both spawning and nonspawning) increased for each proposed seasonal minimum flow relative to former minimum flows, with substantial increases for spawning sites. Our results contribute to an understanding of how regulated flows affect available habitats for imperiled species. Flow managers can use these findings to regulate discharge more effectively and to create and maintain important habitats during critical periods for priority species.

Diel Patterns and Temporal Trends in Spawning Activities of Robust Redhorse and River Redhorse in Georgia, Assessed Using Passive Acoustic Monitoring

AbstractThe conservation of imperiled species depends upon understanding threats to the species at each stage of its life history. In the case of many imperiled migratory fishes, understanding how timing and environmental influences affect reproductive behavior could provide managers with information critical for species conservation. We used passive acoustic recorders to document spawning activities for two large‐bodied catostomids (Robust Redhorse Moxostoma robustum in the Savannah and Broad rivers, Georgia, and River Redhorse M. carinatum in the Coosawattee River, Georgia) in relation to time of day, water temperature, discharge variation, moonlight, and weather. Robust Redhorse spawning activities in the Savannah and Broad rivers were more frequent at night or in the early morning (0100–0400 hours and 0800–1000 hours, respectively) and less frequent near midday (1300 hours). Spawning attempts in the Savannah and Broad rivers increased over a 3–4‐d period and then declined. River Redhorse spawning activities in the Coosawattee River peaked on the first day of recording and declined over four subsequent days; diel patterns were less discernible, although moon illumination was positively associated with spawning rates, which was also observed for Robust Redhorses in the Savannah River. Spawning activity in the Savannah and Broad rivers was negatively associated with water temperature, and spawning activity increased in association with cloud cover in the Savannah River. A large variation in discharge was only measured in the flow‐regulated Savannah River and was not associated with spawning attempts. To our knowledge, this is the first study to show diel and multiday patterns in spawning activities for any Moxostoma species. These patterns and relationships between the environment and spawning activities could provide important information for the management of these species downstream of hydropower facilities.

Passive Acoustic Monitoring to Detect Spawning in Large‐Bodied Catostomids

AbstractDocumenting timing, locations, and intensity of spawning can provide valuable information for conservation and management of imperiled fishes. However, deep, turbid or turbulent water, or occurrence of spawning at night, can severely limit direct observations. We have developed and tested the use of passive acoustics to detect distinctive acoustic signatures associated with spawning events of two large‐bodied catostomid species (River Redhorse Moxostoma carinatum and Robust Redhorse Moxostoma robustum) in river systems in north Georgia. We deployed a hydrophone with a recording unit at four different locations on four different dates when we could both record and observe spawning activity. Recordings captured 494 spawning events that we acoustically characterized using dominant frequency, 95% frequency, relative power, and duration. We similarly characterized 46 randomly selected ambient river noises. Dominant frequency did not differ between redhorse species and ranged from 172.3 to 14,987.1Hz. Duration of spawning events ranged from 0.65 to 11.07s, River Redhorse having longer durations than Robust Redhorse. Observed spawning events had significantly higher dominant and 95% frequencies than ambient river noises. We additionally tested software designed to automate acoustic detection. The automated detection configurations correctly identified 80–82% of known spawning events, and falsely indentified spawns 6–7% of the time when none occurred. These rates were combined over all recordings; rates were more variable among individual recordings. Longer spawning events were more likely to be detected. Combined with sufficient visual observations to ascertain species identities and to estimate detection error rates, passive acoustic recording provides a useful tool to study spawning frequency of large‐bodied fishes that displace gravel during egg deposition, including several species of imperiled catostomids.

Genetic Characterization of the Savannah and Pee Dee River Populations of Robust Redhorse (Moxostoma robustum) with Conservation Implications

Robust Redhorse (Moxostoma robustum) is a deep-dwelling catostomid that lives in southeastern rivers of the United States. After being lost to science for about 100 years, M. robustum was rediscovered in the 1980s by the Georgia DNR and is a federal species of special concern. Our goal was to genetically characterize populations of M. robustum in the Savannah and Pee Dee rivers based on genetic diversity and population structure using a suite of ten microsatellites. Substantial levels of population structure were detected between rivers (RST = 0.308), with high genetic diversity (0.81–0.87) and low inbreeding in both systems. Long-term estimates of effective population sizes were very high for both systems, but contemporary estimates were substantially lower, with the Pee Dee River estimate being of concern from a conservation standpoint. Their long life span and overlapping generations result in a high potential for across-year-class spawning and are likely contributing to the maintenance of high genet...

Modelling riverine habitat for robust redhorse: assessment for reintroduction of an imperilled species

A critical component of a species reintroduction is assessment of contemporary habitat suitability. The robust redhorse, Moxostoma robustum (Cope), is an imperilled catostomid that occupies a restricted range in the south-eastern USA. A remnant population persists downstream of Blewett Falls Dam, the terminal dam in the Pee Dee River, North Carolina. Reintroduction upstream of Blewett Falls Dam may promote long-term survival of this population. Tillery Dam is the next hydroelectric facility upstream, which includes a 30 rkm lotic reach. Habitat suitability indices developed in the Pee Dee River were applied to model suitable habitat for proposed minimum flows downstream of Tillery Dam. Modelling results indicate that the Tillery reach provides suitable robust redhorse habitat, with spawning habitat more abundant than non-spawning habitat. Sensitivity analyses suggested that suitable water depth and substrate were limiting physical habitat variables. These results can inform decisions on flow regulation and guide planning for reintroduction of the robust redhorse and other species.

RELATIONSHIPS BETWEEN RIVER DISCHARGE AND ABUNDANCE OF AGE 0 REDHORSES (MOXOSTOMA SPP.) IN THE OCONEE RIVER, GEORGIA, USA, WITH IMPLICATIONS FOR ROBUST REDHORSE

ABSTRACTRobust redhorse (Moxostoma robustum) and notchlip redhorse (M. collapsum) are two species of redhorses that reside in the lower Oconee River, Georgia. Robust redhorse is listed as a state endangered species in Georgia and North Carolina, and attempts to investigate factors affecting its reproductive success have met with limited success. Therefore, catch of robust redhorse young were combined with catch of notchlip redhorse to increase sample size. These congeners with similar spawning repertoire were assumed to respond similarly to environmental conditions. River discharge during spawning and rearing seasons may affect abundance of both redhorses in the lower Oconee River. An information‐theoretic approach was used to evaluate the relative support of models relating abundance of age 0 redhorses to monthly discharge statistics that represented magnitude, timing, duration, variability and frequency of river discharge events for April through June 1995–2006. The best‐approximating model indicated a negative relationship between the abundance of redhorses and mean maximum river discharge and the number of high pulses during June as well as a positive relationship with intermediate duration of low flows during April–June. This model is 9.6 times more plausible than the next best‐fitting model, which revealed a negative relationship between the abundance of redhorses and mean maximum river discharge during May and the number of high pulses during June as well as a positive relationship between abundance and intermediate duration of low flows during April–June. Management implications from the results indicate low‐stable flows for at least a 2‐week period during spawning and rearing may increase reproductive success of robust and notchlip redhorses. Copyright © 2012 John Wiley &amp; Sons, Ltd.

REDD DEWATERING EFFECTS ON HATCHING AND LARVAL SURVIVAL OF THE ROBUST REDHORSE

ABSTRACTRiverine habitats have been altered and fragmented from hydroelectric dams and change spatially and temporally with hydropower flow releases. Hydropeaking flow regimes for electrical power production inundate areas that create temporary suitable habitat for fish that may be rapidly drained. Robust redhorse Moxostoma robustum, an imperiled, rare fish species, uses such temporary habitats to spawn, but when power generation ceases, these areas are dewatered until the next pulse of water is released. We experimentally simulated the effects of dewatering periods on the survival of robust redhorse eggs and larvae in the laboratory. Robust redhorse eggs were placed in gravel in eyeing‐hatching jars (three jars per treatment) and subjected to one of four dewatering periods (6, 12, 24 and 48 h), followed by 12 h of inundation for each treatment, and a control treatment was never dewatered. Egg desiccation was observed in some eggs in the 24‐ and 48‐h treatments after one dewatering period. For all treatments except the control, the subsequent dewatering period after eggs hatched was lethal. Larval emergence for the control treatment was observed on day 5 post‐hatching and continued until the end of the experiment (day 21). Larval survival was significantly different between the control and all dewatering treatments for individuals in the gravel. These findings support the need for hydropower facilities to set minimum flows to maintain inundation of spawning areas for robust redhorse and other species to reduce dewatering mortality. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Fine sediment affects on survival to emergence of robust redhorse

Robust redhorse (Moxostoma robustum) is a rare riverine sucker for which life history information is scarce. Spawning occurs over loose gravel substrate and eggs and larvae may be adversely affected by fine sediments among the gravel. A 2-year study was conducted to determine the threshold at which fine sediments are detrimental to successful egg incubation and larval emergence. Year 1 gravel treatments contained 0, 25, 50, and 75% fine sediments. Mean survival during Year 1 ranged from 63.5% in the 0% fine sediment treatment to 0% in the 75% fine sediment treatment. The results also indicated an adverse affect threshold between 0 and 25% fine sediment. Year 2 gravel treatments contained 0, 5, 10, 15, 20, and 25% fine sediments. Mean survival during Year 2 ranged from 69.8% in the 0% treatment to 9.1% in the 25% treatment. Year 2 results also identified the 15% fine sediment treatment as the threshold at which survival began to decline. Substrates at one known spawning area used by robust redhorse typically contain 25 to 50% fine sediment, but the spawning act cleans some fines from the egg pocket. Whether the “cleaning” that results from the spawning act reduces the fines sufficiently to avoid adverse effects is unknown. According to our results, survival rates of robust redhorse eggs and larvae are predicted to be about 8.0% or less when fine sediment is >25%.

Capture Probability and Behavioral Response of the Robust Redhorse, a Cryptic Riverine Fish, to Electrofishing

AbstractConservation and management of riverine species, such as the robust redhorse Moxostoma robustum, can be hindered by incomplete understanding of their population status. Behavioral responses to sampling methods and susceptibility to capture by a particular gear type have implications for the reliability of population assessments yet are rarely evaluated. Consequently, we used radio‐tagged robust redhorses in the Ocmulgee River, Georgia, to estimate capture probability when sampled with standard boat electrofishing techniques and to assess behavioral responses of individuals to single and repeated exposures to electrofishing, the recommended sampling method for this species. Transects containing one to eight radio‐tagged individuals were sampled. The positions of radio‐tagged individuals were recorded before electrofishing and at 1‐h, 24‐h, and 3–5‐d intervals after sampling. We estimated robust redhorse abundance and capture probability by treating each transect as analogous to a repeated sample in time. Only one radio‐tagged individual and six untagged individuals were captured after 7.46 h of effort. The radio‐tagged fish did not exhibit an immediate response to boat electrofishing, but some did move from their original position after electrofishing. Mean movement was 0.15 km after 1 h, 0.19 km after 24 h, and 0.23 km after 3–5 d. However, this movement was similar to that exhibited by fish located at similar intervals during a related telemetry study without exposure to electrofishing. A mean capture probability of 0.031 with a 95% Bayesian credibility interval of 0.002–0.111 was estimated from the best‐approximating model. Electrofishing is not a particularly effective method for capturing this species; therefore, inferences about population size and distribution of this or other cryptic species need to account for low detection probabilities associated with electrofishing. Alternative approaches or multiple strategies should be considered when assessing the status of such species.

Post‐release movements and habitat use of robust redhorse transplanted to the Ocmulgee River, Georgia

Abstract Robust redhorse Moxostoma robustum is an imperiled, potadromous fish in the south‐eastern USA. Initial recovery efforts have focused on supplementing existing populations and establishing refugial populations through extensive stocking programmes. However, assessment of the success of these programmes has not yet been conducted, and there are few reports evaluating the effectiveness of such programmes with other potadromous species. Radio telemetry was employed to assess the effectiveness of a stocking programme aimed at addressing whether stocked individuals would remain in an area free of introduced predators and ascertaining the ability of stocked fish to integrate into a resident population. Hatchery‐reared robust redhorse were captured from refugial populations established in other river systems and were transferred to the Ocmulgee River, Georgia where a population of hatchery‐reared individuals and an unknown number of wild fish reside. These transferred robust redhorse exhibited an exploratory phase for the first 3 months before adopting behaviour patterns, including spawning migrations, that were consistent with those reported for wild fish in other systems. However, some individuals seemed unable to locate suitable spawning habitat. Approximately half of the radio‐tagged fish remained within the area free of introduced predators. At least some radio‐tagged robust redhorse fully integrated into the resident population as evidenced by their presence in spawning aggregations with resident individuals. The effectiveness of a stocking programme is dependent upon the ability of stocked individuals to integrate into an existing population or replicate the behaviour and functionality of a resident population. Evaluations of stocking programmes should incorporate assessments of behaviour in addition to surveys to estimate abundance and survivorship and genetic assessments of augmentation of effective population sizes. Published in 2008 by John Wiley &amp; Sons, Ltd.

Size of Spawning Population, Residence Time, and Territory Shifts of Individuals in the Spawning Aggregation of a Riverine Catostomid

Little is known about the behavior of individual fish in a spawning aggregation, specifically how long an individual remains in an aggregation. We monitored Moxostoma robustum (Cope) (Robust Redhorse) in a Savannah River spawning aggregation during spring 2004 and 2005 to provide an estimate of the total number of adults and the number of males comprising the aggregation and to determine male residence time and movements within a spawning aggregation. Robust Redhorse were captured using prepostioned grid electrofishers, identified to sex, weighed, measured, and implanted with a passive integrated transponder. Spawning aggregation size was estimated using a multiple census mark-and-re- capture procedure. The spawning aggregation seemed to consist of approximately the same number of individuals (82-85) and males (50-56) during both years of this study. Individual males were present for a mean of 3.6 ± 0.24 days (± SE) during the 12-day spawning period. The mean distance between successive re- captures of individual males was 15.9 ± 1.29 m (± SE). We conclude that males establish spawning territories on a daily basis and are present within the spawning aggregation for at least 3-4 days. The relatively short duration of the aggregation may be the result of an extremely small population of adults. However, the behav- ior of individuals has the potential to influence population estimates made while fish are aggregated for spawning.

Demographics of the spawning aggregations of four catostomid species in the Savannah River, South Carolina and Georgia, USA

Abstract – Differences in the life history strategies employed by otherwise ecologically similar species of a fish assemblage may be an important factor in the coexistence of these species and is an essential consideration in the conservation and management of these assemblages. We collected scales to determine age and growth of four species of the catostomid assemblage (northern hogsucker Hypentelium nigricans, spotted sucker Minytrema melanops, notchlip redhorse Moxostoma collapsum and robust redhorse Moxostoma robustum) of the Savannah River, Georgia–South Carolina in spring 2004 and 2005. Robust redhorse was the largest species; reaching sexual maturity at an older age and growing faster as a juvenile than the other species. Spotted sucker did not achieve the same size as robust redhorse, but reached sexual maturity at younger ages. Notchlip redhorse was intermediate between the abovementioned two species in age at maturity and size. Northern hogsucker was the smallest species of the assemblage and reached the sexual maturity at the age of three. Both robust redhorse and spotted sucker were sexually dimorphic in size‐at‐age. The range of life history strategies employed by Savannah River catostomids encompasses the range of life history strategies exhibited within the family as a whole.

Flow Preferences for Juvenile Robust Redhorses in an Experimental Mesocosm: Implications for Developing Sampling Protocols

AbstractThe robust redhorse Moxostoma robustum, originally described by Edward Cope in 1870 from specimens collected from the Yadkin River, North Carolina, apparently went unnoticed until 1991 when it was rediscovered in the lower Oconee River, Georgia. Despite extensive surveys and an ongoing, decade‐long restoration program, wild‐spawned juveniles 30–410 mm in total length have not been collected. This project experimentally evaluated one hypothesis (flow class use) that seeks to explain the absence of juvenile robust redhorses from the catch. Two experimental mesocosms were used to determine whether juvenile robust redhorses use flow classes in proportion to their availability. Pond‐reared juveniles were exposed to four flow‐based habitat types (eddies = −0.12 to −0.01 m/s, slow flow = 0.00–0.15 m/s, moderate flow = 0.16–0.32 m/s, and backwaters) in four 10‐d trials, in which 16 pond‐reared test fish were used per trial, with replacement. Location data were recorded hourly during daytime hours for each fish in all trials and evaluated with a log‐linear, chi‐square model. In winter, test fish showed a preference for eddies and backwaters and avoided slow to moderate flows. In early spring, test fish showed a preference for eddies and avoided the moderate flows. Current field sampling for juvenile robust redhorses has not targeted the flow classes used by fish in this experiment; however, collection of wild‐caught juveniles may be improved by sampling in eddies and their associated transitional areas.

Catostomid Fishes of the Wateree River, South Carolina

Fish surveys throughout the Wateree River in 2004–2005 documented the presence of 8 catostomid species—Carpiodes sp. cf. Cyprinus (quillback), Erimyzon oblongus (creek chubsucker), Ictiobus bubalus (smallmouth buffalo), Minytrema melanops (spotted sucker), Moxostoma collapsum (notchlip redhorse), M. macrolepidotum (shorthead redhorse), Scartomyzon rupiscartes (striped jumprock), and Scartomyzon sp. undescribed species (brassy jumprock)—but failed to document C. sp. cf. velifer (highfin carpsucker), Moxostoma sp. cf. Erythrurum (Carolina redhorse), or M. robustum (robust redhorse). Four native (quillback, spotted sucker, notchlip redhorse, and shorthead redhorse) and the nonnative small-mouth buffalo were collected in sufficient numbers to allow observations of unique aggregations. Based on time of year, expression of milt, presence of tubercles, and published thermal preferenda during spawning, we believe these aggregations were associated with spawning, although direct observations of spawning behavior were not made. Spotted suckers used Piedmont and transitional-zone habitats early in the year and also aggregated in larger numbers in the mouths of blackwater Coastal Plain tributaries. Low catches of spotted sucker in riffle habitat in the Wateree River at temperatures exceeding 14 °C appears anomalous and merits further investigation. All other suckers were collected predominantly in areas of gravel, cobble, and bedrock in the Piedmont and transitional zone; aggregations of quillback, shorthead redhorse, and then notchlip redhorse successively followed high spotted sucker catches. The nonnative smallmouth buffalo appeared to use these same habitats during the entire time when quillback, shorthead redhorse, and notchlip redhorse were present, although smallmouth buffalo were collected at low catch rates. The elevated temperatures at which notchlip redhorse aggregated appeared anomalous and merits further investigation.

The genetic variation and biogeography of catostomid fishes based on mitochondrial and nucleic DNA sequences

The genetic variation, phylogeny and biogeography of catostomid fishes were investigated based on mitochondrial cytochrome b and nuclear 18S‐ITS1‐5.8S DNA sequences. The pair‐wise genetic distance of cytochrome b for 17 catostomids varied considerably, from 1·00% (Chasmistes brevirostris and Deltistes luxatus) to 23·3% (Cycleptus elongatus and Moxostoma anisurum). The size of the 18S‐ITS1‐5.8S sequence ranged from 315 bp (Moxostoma robustum) to 575 bp (Ictiobus cyprinellus). The 18S‐5.8S region was conservative and the length of ITS1 regions was found to vary considerably among the seven catostomids. It is interesting that the primitive I. cyprinellus and Myxocyprinus asiaticus had longer ITS1 regions than suckers from the Catostominae. Based on the nucleotide substitution model, the nuclear 18S‐5.8S gene had a faster evolution rate than the mitochondrial cytochrome b gene. In a phylogenetic analysis, 17 catostomids from 14 genera representing three subfamilies were not distinctly divergent. Nevertheless, three major genetically divergent clades were identified. Clade I (95% bootstrap) included general Catostomus, Thoburnia, Xyrauchen, Chasmistes and Deltistes. Clade II (94% bootstrap) included Hypentelium, Moxostoma and Scartomyzon. Clade III (77% bootstrap) was a monophyletic Ictiobinae containing I. cyprinellus and Carpiodes carpio. The biogeography of old world catostomids followed a disperse event, and the speciation of the extant catostomids was a vicariance event. The earliest catostomid evolved in Asia from one branch of ostariophysans in the early Tertiary. Before the Eocene, catostomids belonging to the genus Amyzon had a wide, trans‐Pacific distribution over Asia and North America. Later, oceanic ingression and the Tertiary glacial event forced catostomids to evolve on both mainlands, respectively. The present disjunct distribution pattern of catostomids was presumably due to competitive pressure from cyprinids, geographical events, their Late Cenozoic radiation in North America and glacial events. The divergence time based on the mitochondrial and nuclear DNA sequences suggests that catostomids began to diverge in the early or mid‐Miocene, which agrees with the fossil evidence.

Spatial and temporal segregation of spawning habitat by catostomids in the Savannah River, Georgia and South Carolina, U.S.A.

Spawning aggregations of five species of catostomids were observed on the two mid‐channel gravel bars of the Savannah River, Georgia and South Carolina, in 2004 and 2005 to assess the degree of spatial and temporal overlap in the use of this habitat and determine the habitat preferences leading to segregation. Spawning catostomids showed a considerable amount of temporal overlap in their use of these mid‐channel gravel bars. The observed temporal overlap was consistent between 2004 and 2005 and corresponded to temperatures at which species were present. The distribution of catostomids was not uniform at the upstream gravel bar. Carpsuckers Carpiodes sp., spotted sucker Minytrema melanops and robust redhorse Moxostoma robustum both demonstrated some spatial overlap with notchlip redhorse Moxostoma collapsum; however, their overall distributions were different from one another. Northern hogsucker Hypentelium nigricans was present across the gravel bars, apparently as an egg predator. Spawning catostomids segregated based on flow, depth, slope and substratum size. Whether due to limited habitat availability or changes in the timing of reproduction due to altered cues, temporal and spatial overlap occurs between spawning catostomids despite the apparent partitioning of available spawning habitat. It is unclear, however, if this overlap results in excessive mortality in the early life‐history stages of these species. Results suggest spatial overlap among catostomid species was minimized due to species spawning in areas within a narrow range of conditions. Intraspecific interactions such as nest site superimposition or disturbance may be a concern.