Mottled Sculpin Research Articles

Seasonal trophic niche width and overlap of mottled sculpin and brown trout in a regulated high‐elevation river

AbstractIn temperate ecosystems, resource availability fluctuates seasonally due to changes in environmental conditions and productivity. Intra‐ and inter‐specific trophic niche overlap under resource limitation is a measure of competitive interactions and influences species coexistence and community dynamics, but patterns of this overlap are influenced by anthropogenic activities. To investigate seasonal trophic niche dynamics of coexisting fish species in a flow‐altered river, we analysed prey resources, stomach content samples and stable isotope signatures of mottled sculpin Cottus bairdii and juvenile brown trout Salmo trutta in the Blue River, Colorado, USA, a high‐elevation oligotrophic river. Prey biomass (i.e. benthic macroinvertebrates) peaked in spring and declined through summer and autumn. Stomach content and stable isotope analysis results showed that diet composition of mottled sculpin and brown trout varied seasonally in response to changes in prey availability. Stomach content analysis results revealed that in autumn, both species exhibited the highest frequency of empty stomachs and expanded population trophic niches due to increased inter‐individual diet variation despite decreased individual trophic niche breadth. Inter‐specific trophic niche overlap was relatively high across all seasons, but the lowest degree of overlap occurred in autumn of both years when prey availability was lowest. Isotopic analysis revealed similar trends to stomach content analysis, of wider isotopic niches and reduced overlap in autumn compared to spring. Our data indicated that seasonal variation affected individual‐ and population‐level trophic niche dynamics and inter‐specific niche overlap between mottled sculpin and brown trout. This trophic segregation under resource limitation may serve as a mechanism that facilitates species coexistence in a flow‐regulated, oligotrophic river.

A multisensory perspective on near-field detection and localization of hydroacoustic sources

This paper gives a brief synopsis of the research career of S.C. in fish bioacoustics with an emphasis on dipole near fields. The hydroacoustic nature of the dipole near field and the effective stimuli to lateral line and auditory systems combine to produce a multisensory, range-fractionated region that is critically important to many fish behaviors. The mottled sculpin and goldfish lateral lines encode the spatial complexities of the near field as spatial excitation patterns along the body surface to provide instantaneous snapshots of various source features such as distance, orientation, and direction of movement. In contrast, the pressure-sensitive channel of the goldfish auditory system [the anterior swim bladder (SB)-saccule complex] encodes the spatial complexities in a temporal fashion whenever the position or orientation of the source changes with respect to the anterior SB. A full appreciation for how these somatotopic and egocentric representations guide fish behavior requires an understanding of how multisensory information, including vision, is combined in sensorimotor regions of the brain to effect behavior. A brief overview of vertebrate brain organization indicates that behaviors directed to or away from hydroacoustic sources likely involve a variety of mechanisms, behavioral strategies, and brain regions.

Sub‐seasonal correlation between growth and survival in three sympatric aquatic ectotherms

Animals experience seasonally changing conditions in temperate regions, thus population vital rates change seasonally. However, knowledge is lacking on patterns of seasonal correlation between growth and survival in sympatric ectotherms, and this knowledge gap limits our understanding of environmental change impacts on animal populations and communities. Here, we investigated sub‐seasonal (two‐month intervals) correlation between growth and survival in three stream fishes (bluehead chubNocomis leptocephalus, creek chubSemotilus atromaculatusand mottled sculpinCottus bairdii) in South Carolina, USA, via a mark–recapture survey over 28 months. We found that patterns of temporal correlation between the population vital rates differed among the sympatric species. Growth increased and survival decreased with water temperature in two eurythermal species, resulting in negative correlation between growth and survival. Growth peaked in sub‐seasons with an intermediate water temperature range in a third stenothermal species, while survival decreased with water temperature for this species too. Consequently, there was not significant negative or positive correlation between sub‐seasonal growth and survival in the stenothermal species. Body condition (weight at given length) decreased from May through November in all three species, providing a potential physiological explanation for why survival rates were lower during this period. Negative correlation among population vital rates stabilizes population size over time and buffers animal populations from environmental change because the vital rates are not affected simultaneously in the same direction, indicating some degree of resiliency in the face of climate changes in the two eurythermal species. However, such a demographic mechanism of resiliency could be maintained so long as climate warming does not exceed optimal growth temperature, above which negative correlation between growth and survival may no longer be maintained.

Rapid colonisation post‐displacement contributes to native fish resilience

AbstractNative freshwater fish are experiencing global declines. Determining what drives native fish resilience to disturbance is crucial to understanding their persistence in the face of multiple stressors. Fish colonisation ability may be one factor affecting population resilience after disturbance. We conducted displacement experiments in headwater streams in Wyoming, USA, to evaluate mottled sculpin (Cottus bairdii) and mountain sucker (Catostomus platyrhynchus) colonisation ability. Specifically, we (1) determined whether fish could colonise sites rapidly after displacement, (2) evaluated site‐level factors affecting colonisation, and (3) compared species‐level differences in movement and colonisation capabilities. Mountain sucker recovered to pre‐displacement abundances within 6–11 weeks, but mottled sculpin were still at slightly reduced abundances. For both species, the majority of colonists were unmarked new individuals and size–structure was similar to pre‐displacement size–structure. Fish colonisation was best predicted by pre‐displacement abundance and an interaction between per cent riparian cover and species identity. The slower colonisation rate of mottled sculpin may relate to movement ability as average daily movement rate and movement extent were significantly greater for mountain sucker. Our results demonstrate that colonisation is one mechanism allowing fish populations to be resilient in the face of disturbance and that species' traits provide insight into fish colonisation capabilities. Experimental approaches provide mechanistic insight into colonisation dynamics, enhancing our understanding of native fish resilience in degraded stream ecosystems and their response to restoration actions.

Comparison of Multipiscivore Foraging Success on Native and Invasive Prey Fish under Variable Light Intensities

AbstractPiscivorous fishes attack and consume a variety of prey; however, few studies have examined interactions of multiple predators with multiple prey species. The situational complexity of foraging at different times of day was explored by examining the interactions of paired native predators (Burbot Lota lota or Smallmouth Bass Micropterus dolomieu) with either native (Mottled Sculpin Cottus bairdii) or invasive (Round Goby Neogobius melanostomus) benthic prey. The study allowed the comparison of a pursuit predator (Smallmouth Bass) and an ambush predator (Burbot). Trials were performed under natural relevant lighting conditions with downwelling light intensity and emission spectrum matched to the irradiance at a 10‐m depth in the St. Louis River estuary during the summer at night, civil twilight, sunrise, and midmorning. Smallmouth Bass were more active and initiated 1,510 reactions that resulted in the successful capture of 61 Round Goby and 103 Mottled Sculpin, whereas Burbot initiated 475 reactions resulting in 24 successful retentions, including 9 Round Goby and 15 Mottled Sculpin. The percentage of successful retentions was greater for Smallmouth Bass (10.9%) than for Burbot (5%). Reaction probabilities to each prey differed significantly, which resulted in a two‐fold increase in attacks on Mottled Sculpin compared with Round Goby within the same time period. Reaction distances for both predators did not differ regarding prey species, but Smallmouth Bass reacted from farther away than did Burbot (maximum reaction distances of 159 and 98 cm, respectively). Greater success of native predators on native prey has likely caused higher mortality on native prey populations due to greater predator success, while capturing invasive prey decreases the net energy intake.

Spatial and seasonal occurrence of semi-volatile organic compounds (SVOCs) in fish influenced by snowmelt and municipal effluent discharge

In the present study we examined spatial and seasonal trends in the levels of a wide suite of semi-volatile organic compounds (SVOCs) in brown trout (Salmo trutta) and mottled sculpin (Cottus bairdii) in East Canyon Creek, Utah, USA, an effluent-dominated stream during summer months. Fish samples were collected from four sampling sites, including one reference site upstream, and three sites at incremental distances downstream of the effluent discharge over multiple seasons. The samples were analyzed for 218 lipophilic contaminants, including pesticides and their metabolites, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and polybrominated diphenyl ethers (PBDEs) and other flame retardants. Some PAHs, pesticides and their metabolites, PCBs, PBDEs and other flame retardants were measured in mottled sculpin (11 analytes) and brown trout (17 analytes). Hexachlorobenzene (HCB), p,p′-DDE, BDE-47 and triphenyl phosphate (TPHP) were the most frequently detected contaminants in mottled sculpin and brown trout, while BDE-47 and p,p′-DDE were measured at the highest concentrations, reaching up to 73 and 19 ng/g wet weight, respectively. Our results indicated that snowmelt did not alter accumulation of the examined lipophilic contaminants, and no consistent seasonal differences were observed in their accumulation. A spatial pattern was observed for PBDE congeners, where lowest levels were measured in fish tissues from a reference site, and highest concentrations were measured in fish collected downstream of the effluent discharge, indicating that municipal effluent discharge contributes to the elevated PBDE levels in fish residing in this effluent-dominated stream. We further calculated screening level consumption risks following United States Environmental Protection Agency (EPA) methods, and identified the importance of considering discharge gradients in effluent-dominated systems during bioaccumulation assessments.

Sensitivity of Warm-Water Fishes and Rainbow Trout to Selected Contaminants

Guidelines for developing water quality standards allow U.S. states to exclude toxicity data for the family Salmonidae (trout and salmon) when deriving guidelines for warm-water habitats. This practice reflects the belief that standards based on salmonid data may be overprotective of toxic effects on other fish taxa. In acute tests with six chemicals and eight fish species, the salmonid, Rainbow Trout (Oncorhynchus mykiss), was the most sensitive species tested with copper, zinc, and sulfate, but warm-water species were most sensitive to nickel, chloride, and ammonia. Overall, warm-water fishes, including sculpins (Cottidae) and sturgeons (Acipenseridae), were about as sensitive as salmonids in acute tests and in limited chronic testing with Lake Sturgeon (Acipenser fulvescens) and Mottled Sculpin (Cottus bairdi). In rankings of published acute values, invertebrate taxa were most sensitive for all six chemicals tested and there was no trend for greater sensitivity of salmonids compared to warm-water fish.

Warmer temperatures interact with salinity to weaken physiological facilitation to stress in freshwater fishes.

Management of stressors requires an understanding of how multiple stressors interact, how different species respond to those interactions and the underlying mechanisms driving observed patterns in species’ responses. Salinization and rising temperatures are two pertinent stressors predicted to intensify in freshwater ecosystems, posing concern for how susceptible organisms achieve and maintain homeostasis (i.e. allostasis). Here, glucocorticoid hormones (e.g. cortisol), responsible for mobilizing energy (e.g. glucose) to relevant physiological processes for the duration of stressors, are liable to vary in response to the duration and severity of salinization and temperature rises. With field and laboratory studies, we evaluated how both salinity and temperature influence basal and stress-reactive cortisol and glucose levels in age 1+ mottled sculpin (Cottus bairdii), mountain sucker (Catostomus platyrhynchus) and Colorado River cutthroat trout (Oncorhynchus clarki pleuriticus). We found that temperature generally had the greatest effect on cortisol and glucose concentrations and the effect of salinity was often temperature dependent. We also found that when individuals were chronically exposed to higher salinities, baseline concentrations of cortisol and glucose usually declined as salinity increased. Reductions in baseline concentrations facilitated stronger stress reactivity for cortisol and glucose when exposed to additional stressors, which weakened as temperatures increased. Controlled temperatures near the species’ thermal maxima became the overriding factor regulating fish physiology, resulting in inhibitory responses. With projected increases in freshwater salinization and temperatures, efforts to reduce the negative effects of increasing temperatures (i.e. increased refuge habitats and riparian cover) could moderate the inhibitory effects of temperature-dependent effects of salinization for freshwater fishes.

Anthropogenic land‐use change intensifies the effect of low flows on stream fishes

Abstract As ecosystems experience simultaneous disturbances, it is critical to understand how multiple stressors interact to affect ecological change. Land‐use change and extreme flow events are two important stressors that could interact to affect fish populations. We evaluated the individual and interactive effects of discharge and land‐use change associated with oil and natural gas development on populations of two stream fishes over a 7‐year period. We used repeated‐state (i.e. abundance trends) and rate (i.e. colonization and persistence) responses to advance our understanding of flow‐ecology relationships in a multiple‐stressor framework. Overall, fish abundance, colonization and persistence declined as discharge decreased. The effect of land‐use change associated with oil and natural gas development differed between species, with the abundance of Mottled Sculpin declining and Mountain Sucker increasing as land‐use change increased. We found both synergistic and antagonistic interactions between discharge and land‐use change. Land‐use change intensified the effect of low flows for Mottled Sculpin and lead to greater variability in responses to flow for Mountain Sucker. These differences between species' responses are likely due to differences in their physiological tolerances and behavioural adaptations to disturbance. Synthesis and applications. Our research provides empirical evidence for the complex interactions that can arise between discharge and anthropogenic land‐use change. Management efforts to reduce inputs of sediments and chemical contaminants associated with land‐use change (e.g. silt fences, vegetative buffers) and promote quality refuge habitats (i.e. in‐stream habitat restoration) could help mitigate the negative effects of low‐flow extremes on stream fishes. Further development of flow‐ecology relationships in a multiple‐stressor framework will help guide management of stream fishes, and provide a better understanding of the mechanisms underlying responses of different species.

A mechanistic understanding of ecological responses to land‐use change in headwater streams

AbstractAnthropogenic activities, such as oil and natural gas development (ONGD), have significantly altered the landscape. It is often challenging to identify the mechanistic processes underlying ecological responses to land‐use change (LUC). In aquatic ecosystems, alterations to habitat and food availability and water quality associated with increased LUC are key mechanistic pathways that deserve management consideration. We used structural equation modeling to evaluate how LUC associated with ONGD could influence macroinvertebrate and fish across 40 sites in six headwater streams in the Wyoming Range of the Upper Green River Basin, Wyoming. The most important mechanistic pathway varied, but responses were frequently driven by a direct effect of LUC or related to changes in food availability and water quality. Habitat complexity was the least important mechanistic pathway in our models. Our results also highlight that responses may reflect an organism's degree of habitat or resource specialization and/or sensitivity to changes in water quality. Habitat pathways were more important for habitat specialists (e.g., Mottled Sculpin, Cottus bairdii), food pathways were more important for food specialists (e.g., Colorado River Cutthroat Trout, Oncorhynchus clarki pleuriticus; Mountain Sucker, Catostomus platyrhynchus), and sensitivity to increased salinity was important for intolerant species (e.g., O. clarki, C. bairdii, and predatory macroinvertebrates). Continued identification of the specific mechanisms underlying species’ responses to increased LUC will aid in the conservation of ecologically and economically important species.

Karyotypes of Cottus cognatus, C. bairdi, and their hybrids in central Pennsylvania

Abstract Karyotypes of the slimy sculpin (Cottus cognatus), the mottled sculpin (C. bairdi), and hybrids of these two species were prepared from specimens collected from the west branch of the Susquehanna River in Lycoming and Clinton counties in Central Pennsylvania. Diploid numbers of 48 and arm numbers of 72 were determined for both species and the hybrids. No sexual dimorphism or chromosomal morphological differences were found in either species or the hybrids. Chromosomal evolution within Cottus is shown to have proceeded by pericentric inversions. A hybrid zone of approximately 10 km is indicated.

Resurgence of Salmonid Herpesvirus-3 Infection (Epizootic Epitheliotropic Disease) in Hatchery-Propagated Lake Trout in Michigan.

Over the past century, populations of Lake Trout Salvelinus namaycush have declined throughout the Great Lakes basin due to overfishing, habitat destruction, introduction of invasive species, and associated recruitment issues from high thiaminase, as well as emerging infectious diseases. To combat these declines, state and federal fishery management agencies undertook substantial stock enhancement efforts, including more stringent regulation of sport and commercial catch limits and increasing hatchery propagation of Lake Trout stocked into Great Lakes basin waterways. One state fish hatchery involved in these rehabilitation efforts experienced mass mortality events in 2012 and 2017. In 2012, following a period of abnormally heavy rain, hatchery staff observed abnormal behavior followed by increased mortalities in two strains of Lake Trout fingerlings, reaching upwards of 20% mortality and totaling a loss of approximately 100,000 fish. In 2017, following another heavy-rain season, 6-8% of 2-year-old Lake Trout experienced morbidity and mortality similar to that observed in 2012. During the 2012 event, Brook Trout Salvelinus fontinalis and splake (Lake Trout×Brook Trout hybrid) reared in flow-through systems receiving water from diseased Lake Trout remained clinically unaffected. Molecular analyses revealed all lots of affected Lake Trout were infected with the salmonid herpesvirus-3 (epizootic epitheliotropic disease virus [EEDV]), a disease that caused complete depopulation of this hatchery in the late 1980s and until 2012 was never again detected in this hatchery or in Michigan. Further sampling detected EEDV in apparently healthy 5-year-old Lake Trout and in wild Mottled Sculpin Cottus bairdii collected in the hatchery source water. The ability of the virus to replicate in tissues of infected fish was verified by exposing naïve Lake Trout to the filtered tissue homogenates of infected fish resulting in similar disease signs. Despite the virus going undetected for many years, these two EEDV episodes clearly demonstrate the continued presence of this deadly herpesvirus in the Great Lakes basin.

Integrating Results of Field Biomonitoring and Mesocosm Experiments To Validate Postspill Impacts of Petroleum Hydrocarbons on Stream Benthic Communities.

We integrated the results of field surveys with a mesocosm experiment to quantify the ecological impacts of a gasoline and diesel spill on a third-order stream in western Colorado (United States). The spill caused a massive fish-kill of brown trout ( Salmo trutta) and mottled sculpin ( Cottus bairdii), which extended several kilometers downstream. Despite significant decreases in petroleum hydrocarbon concentrations, subsequent surveys indicated little recovery of fish populations 4 years after the spill. Benthic macroinvertebrate communities were also affected, yet some metrics commonly used to assess stream ecological integrity (e.g., total abundance and species richness) showed no difference between impacted and reference sites. The failure of some groups to recover 2.5 years after the spill was likely a result of their comparatively slow reproduction and recolonization rates. To support our hypothesis that effects observed in the field resulted from petroleum exposure, we conducted a mesocosm experiment in which benthic macroinvertebrate communities were exposed to a simulated diesel spill. We observed significant decreases in the abundance of most macroinvertebrate groups at the lowest exposure concentration (75 mg/L diesel) and a strong concentration-dependent drift response across all groups. Our study suggests that relatively small petroleum spills can significantly affect stream communities, and these effects may persist several years after sediment concentrations return to background levels.

Effectiveness of shallow water habitat remediation for improving fish habitat in a large temperate river

Loss of shallow water riparian zones in the St. Clair River has reduced availability of nursery areas and refuge for fishes. To remediate habitat losses and provide fish nursery areas, five remediation projects were carried out along the river’s United States bank from 2012 to 2014, replacing seawalls with sloping banks and adding in-stream structure (e.g., root wads and boulders). Project evaluation is necessary to determine success, however there is no standard sampling protocol for shallow habitat in large rivers, especially when both adults and juvenile fishes should be targeted. Therefore, to assess remediation effectiveness and suggest appropriate sampling techniques for large river shorelines, we employed a multi-gear sampling strategy targeting multiple fish species and life history stages at five shoreline remediation and four control sites. We collected juvenile fishes with minnow traps and backpack electrofishing and adult fishes with gillnets. Poisson models were used to evaluate catch per unit effort (CPUE) differences between remediation and control sites for species of management priority (e.g., game fishes and rare species) and taxonomic groups. Model estimates were then used to calculate proportional abundances and compare species composition between site types. Results indicated that electrofishing CPUEs of Darters, mottled sculpin Cottus bairdi, rare threatened and endangered species, and juvenile and adult Centrarchidae were higher at remediation sites than at control sites. Additionally, juvenile Centrarchidae and mottled sculpin had a higher proportional abundance in electrofishing collections at remediation sites than at control sites. In contrast, CPUEs and proportional abundances were similar for all taxonomic and management priority groups of fish collected in minnow traps and gillnets. Electrofishing captured more species and more individuals and is therefore a valuable sampling technique for large river shorelines. Nevertheless, addition of minnow traps and gillnets allowed for a more comprehensive assessment of fish assemblages. Overall, this multi-faceted survey approach demonstrates that shoreline remediation projects were beneficial to recreational and ecologically important species in the St. Clair River.

Evaluating relationships between native fishes and habitat in streams affected by oil and natural gas development

Oil and natural gas (ONG) development can affect aquatic ecosystems through water contamination, water withdrawals and disturbance of soil and vegetation (surface disturbance) from infrastructure development. Research on how these potential sources of watershed and aquatic ecosystem impairment can affect fish assemblages is limited. Fish–habitat relationships were evaluated across stream sites experiencing differing levels of ONG development. Colorado River cutthroat trout, Oncorhynchus clarkii pleuriticus (Cope), and mottled sculpin, Cottus bairdii Girard, presence and abundance were associated with habitat conditions predominantly found in the less disturbed streams, such as higher proportion of shrub cover, greater stream depths and gravel substrate. Mountain sucker, Catostomus platyrhynchus (Cope), appeared to be a habitat generalist and was able to persist in a wide range of conditions, including degraded sites. Natural resource managers can use habitat preferences of these fish species to establish the development plans that mitigate negative effects of ONG development by protecting the aquatic habitats they rely upon.

Which species, how many, and from where: Integrating habitat suitability, population genomics, and abundance estimates into species reintroduction planning.

Extirpated organisms are reintroduced into their former ranges worldwide to combat species declines and biodiversity losses. The growing field of reintroduction biology provides guiding principles for reestablishing populations, though criticisms remain regarding limited integration of initial planning, modeling frameworks, interdisciplinary collaborations, and multispecies approaches. We used an interdisciplinary, multispecies, quantitative framework to plan reintroductions of three fish species into Abrams Creek, Great Smoky Mountains National Park, USA. We first assessed the appropriateness of habitat at reintroduction sites for banded sculpin (Cottus carolinae), greenside darter (Etheostoma blennioides), and mottled sculpin (Cottus bairdii) using species distribution modeling. Next, we evaluated the relative suitability of nine potential source stock sites using population genomics, abundance estimates, and multiple-criteria decision analysis (MCDA) based on known correlates of reintroduction success. Species distribution modeling identified mottled sculpin as a poor candidate, but banded sculpin and greenside darter as suitable candidates for reintroduction based on species-habitat relationships and habitats available in Abrams Creek. Genotyping by sequencing revealed acceptable levels of genetic diversity at all candidate source stock sites, identified population clusters, and allowed for estimating the number of fish that should be included in translocations. Finally, MCDA highlighted priorities among candidate source stock sites that were most likely to yield successful reintroductions based on differential weightings of habitat assessment, population genomics, and the number of fish available for translocation. Our integrative approach represents a unification of multiple recent advancements in the field of reintroduction biology and highlights the benefit of shifting away from simply choosing nearby populations for translocation to an information-based science with strong a priori planning coupled with several suggested posteriori monitoring objectives. Our framework can be applied to optimize reintroduction successes for a multitude of organisms and advances in the science of reintroduction biology by simultaneously addressing a variety of past criticisms of the field.

Same habitat, different species: otolith microchemistry relationships between migratory and resident species support interspecific natal source classification

We tested the hypothesis that otolith trace elemental signatures (microchemistries) of mottled sculpin Cottus bairdi, slimy sculpin C. cognatus, and juvenile coho salmon Oncorhynchus kisutch were predictive of those of juvenile steelhead O. mykiss across many sites within the Lake Michigan basin. Laser ablation inductively coupled plasma mass spectrometry was used to generate otolith microchemistry signatures for each individual fish. For each species pair, statistical correlations of mean otolith concentrations of Mg, Mn, Cu, Zn, Sr, Ba, and Pb for each site were estimated. Linear equations describing these relationships were used to transform juvenile steelhead otolith microchemistry data to those of each of the other species. Transformed otolith microchemistry data were subjected to random forest classifications developed for mottled sculpin, slimy sculpin, and juvenile coho salmon to assess interspecific natal source assignment accuracies. Steelhead otolith concentrations of Sr were significantly correlated with those of each of the other species, whereas otolith concentrations of Ba and Mn were significantly correlated among some species pairs, but not others. Natal source assignment accuracies of juvenile steelhead to site and watershed generally decreased when otolith microchemistry data were transformed to those of mottled sculpin, slimy sculpin, and coho salmon. Miss-assigned fish often classified into nearby watersheds within larger hydrologic units, leading to higher assignment accuracies at coarser geographical resolutions (75–97% correct assignment to hydrologic unit for each species). These findings suggest that applications of otolith microchemistry data may extend beyond the species from which they are collected.

Detection Efficiency of a Portable PIT Antenna for Two Small‐Bodied Fishes in a Piedmont Stream

AbstractPassive integrated transponder (PIT) tags have been used to infer demography and behavior of lotic fishes, but their application has mostly been limited to salmonids. We studied the efficiency of a portable PIT antenna in a small Piedmont stream (mean width = 2.4 m) in South Carolina by comparing two tag sizes (8‐ and 12‐mm full‐duplex tags) applied to two nongame species (Mottled Sculpin Cottus bairdii and Creek Chub Semotilus atromaculatus). A 285‐m stream reach was blocked off under base flow conditions in September 2016, and 8‐ or 12‐mm PIT tags were implanted in 67 Creek Chub (62–138 mm TL) and 65 Mottled Sculpin (60–88 mm TL). Starting at 1 d after tagging, the study reach was sampled with the portable PIT antenna twice daily for five consecutive days, during which apparent survival of tagged fish was assumed. Generalized linear mixed‐effects models with a logistic link identified that detection efficiency depended on species, tag size, body length, and the species × body length interaction. Mottled Sculpin had detection rates of 56% (8‐mm tags) and 79% (12‐mm tags), with 67% of detections occurring in riffle‐dominated sections, whereas Creek Chub had 3% (8‐mm tags) and 16% (12‐mm tags) detection rates, with 62% of detections occurring in pool‐dominated sections. Detection efficiency decreased with body size in Creek Chub but not in Mottled Sculpin; the observed decrease for Creek Chub was most likely attributable to an ontogenetic habitat shift. The reasonably high detection efficiency of Mottled Sculpin, even with 8‐mm tags, suggested that the portable PIT antenna can be a viable option for some species in small streams, allowing individual‐based approaches to studying small‐bodied species or earlier life stages without the need for repeated physical capture and handling.Received May 13, 2017; accepted October 2, 2017Published online November 10, 2017

Survival of Upper Piedmont Stream Fishes Implanted with 8‐mm Passive Integrated Transponder Tags

AbstractWe studied weekly and bimonthly survival of select nongame fishes that were implanted with 8‐mm PIT tags in upper Piedmont streams of South Carolina, USA. Weekly survival in stream enclosures was assessed for a total of 350 tagged individuals and 311 control (untagged) fish (39–101 mm TL; median = 65 mm TL) belonging to six species (Bluehead Chub Nocomis leptocephalus, Creek Chub Semotilus atromaculatus, Yellowfin Shiner Notropis lutipinnis, Mottled Sculpin Cottus bairdii, Northern Hog Sucker Hypentelium nigricans, and Striped Jumprock Moxostoma rupiscartes). Weekly survival rates ranged from 93.3% to 100% among species, with Yellowfin Shiners experiencing the lowest survival rate. Only 2 of the 337 surviving tagged individuals lost their tags (0.6% tag loss). Logistic regression indicated that species and body length were statistically significant predictors of survival and tag retention. Odds ratios indicated that tagged fish were 1.718 times less likely to survive than control fish, but the tagging effect was not statistically significant. Bimonthly survival was estimated by conducting a mark–recapture study from September 2015 to May 2016, which involved tagging 1,413 unique individuals of Bluehead Chub (45–75 mm TL) in a 520‐m stream section and 431 individuals of Mottled Sculpin (45–75 mm) in another 740‐m section. Bayesian state–space analysis of Cormack–Jolly–Seber models indicated that apparent survival did not differ between newly tagged and previously tagged (i.e., recaptured) individuals in any sampling interval, suggesting that the acute and chronic effects of tagging did not differ. Mean bimonthly apparent survival rate was 0.76 (95% credible interval = 0.64–0.86) for Bluehead Chub and 0.74 (95% credible interval = 0.59–0.88) for Mottled Sculpin. Our results indicate that PIT tags can be successfully applied to study the ecology and life history of small‐bodied, nongame fish species, although caution should be exercised when selecting the species and body sizes to be tagged.

Geographic variation in host fish use and larval metamorphosis for the endangered dwarf wedgemussel

Abstract Host fishes play a crucial role in survival and dispersal of freshwater mussels (Unionoida), particularly rare unionids at conservation risk. Intraspecific variation in host use is not well understood for many mussels, including the endangered dwarf wedgemussel (Alasmidonta heterodon) in the USA. Host suitability of 33 fish species for dwarf wedgemussel glochidia (larvae) from the Delaware and Connecticut river basins was tested in laboratory experiments over 9 years. Relative suitability of three different populations of a single host fish, the tessellated darter (Etheostoma olmstedi), from locations in the Connecticut, Delaware, and Susquehanna river basins, was also tested. Connecticut River basin A. heterodon metamorphosed into juvenile mussels on tessellated darter, slimy sculpin (Cottus cognatus), and Atlantic salmon (Salmo salar) parr. Delaware River basin mussels metamorphosed using these three species, as well as brown trout (Salmo trutta), banded killifish (Fundulus diaphanus), mottled sculpin (Cottus bairdii), striped bass (Morone saxatilis), and shield darter (Percina peltata). Atlantic salmon, striped bass, and sculpins were highly effective hosts, frequently generating 5+ juveniles per fish (JPF) and metamorphosis success (MS; proportion of attaching larvae that successfully metamorphose) ≥ 0.4, and producing juveniles in repeated trials. In experiments on tessellated darters, mean JPF and MS values decreased as isolation between the mussel source (Connecticut River) and each fish source increased; mean JPF = 10.45, 6.85, 4.14, and mean MS = 0.50, 0.41, and 0.34 in Connecticut, Delaware, and Susquehanna river darters, respectively. Host suitability of individual darters was highly variable (JPF = 2–11; MS = 0.20–1.0). The results show that mussel–host fish compatibility in A. heterodon differs among Atlantic coastal rivers, and suggest that hosts including anadromous Atlantic salmon and striped bass may help sustain A. heterodon in parts of its range. Continued examination of host use variation, migratory host roles, and mussel–fish interactions in the wild is critical in conservation of A. heterodon and other vulnerable mussel species.