Creek Chub Semotilus Atromaculatus Research Articles

Retention of p‐Chip microtransponders and posttagging survival of small‐bodied stream fishes

AbstractObjectiveObtaining demographic rates often requires complex open‐population capture–mark–recapture (CMR) study designs. Conducting such studies for small‐bodied fishes has been limited in part by excessive mortality after tagging procedures and poor tag retention. As new tag types emerge, information regarding fish survival and tag retention over varying time scales may benefit resource managers to effectively plan future CMR studies. The p‐Chip microtransponder is a 500‐ × 500‐ × 100‐μm tag that is inserted subcutaneously and is read with a handheld laser. Each tag contains a nine‐digit unique identification number. P‐Chip microtransponder tags have been used on a limited number of small‐bodied fishes, with relatively high rates observed for fish survival and tag retention. Information on posttagging survival and retention of p‐Chip microtransponder tags across a range of small‐bodied fish species and tagging locations is needed to inform their effectiveness in future CMR studies.MethodsWe quantified survival and tag retention after p‐Chip microtransponder implantation in Creek Chub Semotilus atromaculatus and Northern Pearl Dace Margariscus nachtriebi in a laboratory environment, and retention of p‐Chip microtransponder tags in Northern Pearl Dace was also quantified over a year‐long field study. We marked 56 Creek Chub and 9 Northern Pearl Dace in the laboratory with p‐Chip microtransponder tags and compared them to an equal number of unmarked individuals over 90 days. We marked 1990 Northern Pearl Dace and conducted recapture events through four seasons (June, September, and October 2022 and June 2023) in four headwater streams of Nebraska.ResultSurvival for Creek Chub was 85% (standard error [SE] = 5.9) and did not differ from control fish survival (95%; SE = 3.2) in the 90‐day laboratory experiment. Survival for Northern Pearl Dace was 89% (SE = 11.0) and did not differ from that of control fish (100%) in the laboratory experiment. Tag retention was 89% (SE = 4.6) for Creek Chub and 100% for Northern Pearl Dace in the laboratory. The p‐Chip microtransponder performed well during the CMR field study, with tag retention for Northern Pearl Dace at 94% across 374 days.ConclusionOur results suggest that the p‐Chip microtransponder minimally affected small‐bodied fish survival and had high tag retention in both the laboratory and field studies. Thus, the p‐Chip microtransponder tag may be appropriate for use in small‐bodied fishes when individual identification is needed in a CMR study.

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.

Non‐random dispersal in sympatric stream fishes: Influences of natural disturbance and body size

AbstractAlthough the prevailing paradigms in spatial ecology have treated dispersal as a stochastic process, there is an increasing awareness that spatial processes are non‐random such that individual characteristics and ecological contexts influence dispersal. Natural disturbance, such as river flooding, is known to stimulate dispersal behaviour, but its interactive effects with individual‐level characteristics (e.g. body size) of potential dispersers remain elusive. It is critical to fill this knowledge gap because anthropogenic impacts (including climate change) alter both disturbance regimes and population structures.Here, we examined how extreme high flows and individual body size combined to influence dispersal of three fishes (creek chubSemotilus atromaculatus, bluehead chubNocomis leptocephalus, and striped jumprockMoxostoma rupicartes) in two streams (740 and 520 m long) in South Carolina, U.S.A. We focused on extreme high flows as a natural disturbance, whereas body size was used as an individual‐level characteristic of dispersers. A total of 5,604 individuals were uniquely marked in the two streams over a >2‐year study period, during which sampling occurred every 2 months.The intensive capture–recapture study revealed differential effects of disturbance and body size among sympatric stream fishes. Extreme high flows increased dispersal of striped jumprock and creek chub, whereas body size influenced dispersal of striped jumprock with larger individuals traveling longer distances. Bluehead chub showed a complex dispersal response. That is, size‐dependence in dispersal emerged only during high‐flow periods.The results of this study build upon previous efforts by providing field‐based evidence of how disturbance and individual characteristics (body size) combine to drive non‐random dispersal and how it varies among sympatric species. This finding is important because metapopulations that are maintained by different non‐random dispersal (i.e. externally or internally driven) may show varied sensitivities to human‐induced environmental changes.

Effects of Interspecific Interactions on Microhabitat Use of Three Helminths Parasitizing Creek Chub (Semotilus atromaculatus) in Southeastern Nebraska

Natural infections of Paulisentis missouriensis (Acanthocephala), Rhabdochona canadensis (Nematoda), and Allocreadium lobatum (Trematoda) in the intestine of creek chub (Semotilus atromaculatus) were studied to determine whether microhabitat use of these helminths was affected by interspecific interactions. Comparison of mean relative positions and intestinal segment use of all 3 helminths revealed no negative interactions among the 3 species. Paulisentis missouriensis appeared entirely unaffected by the presence of either R. canadensis or A. lobatum. Each of the latter 2 species, however, appeared to exhibit some shift toward, rather than away from, the location of P. missouriensis in co-infected hosts. However, the effect size in both cases was small and therefore could be spurious. At higher intensities of co-infecting P. missouriensis, worms of A. lobatum were either distributed far to the anterior or far to the posterior of the intestinal locations occupied by P. missouriensis. This constituted the only evidence in the present investigation for negative interspecific interactions among these 3 frequently co-occurring helminths in this system.

Microhabitat Use of Allocreadium lobatum (Trematoda) in Creek Chub (Semotilus atromaculatus) in Southeastern Nebraska

Microhabitat use of Allocreadium lobatum (Trematoda) in the intestine of creek chub (Semotilus atromaculatus) was studied using natural infections. Seventy-six creek chub harboring only A. lobatum in their intestine provided data on the position of 212 worms along the length of the intestine. Positions of worms within the intestine co-varied strongly with host size and therefore intestinal length; worm positions standardized by intestinal length eliminated this relationship. Analyses of standardized worm positions (worm location) revealed that microhabitat use did not vary with worm size, maturity, or number of eggs in the uterus. Individuals of A. lobatum occurred throughout the intestine, but were concentrated in the posterior 30% of the intestine, regardless of demographic properties of the worms themselves. Standardized niche breadths of parasite infrapopulations suggested strict microhabitat specificity, but nearest-neighbor analyses revealed very little aggregation of worms in infrapopulations beyond what is expected by chance. Overall, trematodes of this species appear to exhibit some microhabitat specificity when examined with snapshot, field-collected data, but there is no clear indication of what mechanism might produce the observed pattern. Use of the intestine by individuals of A. lobatum might be more dynamic than can be revealed by the present investigation or studies similar to it.

Multiscale Habitat Factors Explain Variability in Stream Fish Occurrence in the Ozark Highlands Ecoregion, USA

The dynamic, multiscale nature of stream systems makes it challenging to establish basic ecological principles to guide stream fish conservation and management. For example, finer-scale instream habitat is often constrained by coarser-scale characteristics driving observed species distributions. Additionally, instream environmental variability can result in patchy species distributions within general upstream–downstream occurrence patterns (i.e., variation around a common theme). Groundwater contribution, an often-overlooked habitat characteristic in warmwater systems, has numerous influences on the instream environment and can play a role in fish habitat-use patterns and assemblage structure. We identified multiscale instream habitat characteristics associated with the occurrence probability of 20 Ozark Highland stream fishes. Fishes were surveyed using tow-barge electrofishing in 76 channel unit complexes (i.e., riffle-to-riffle habitat sequences) nested in 20 reaches of northwest Oklahoma and southwest Missouri. We used a multiscale, multispecies generalized linear mixed model to identify relationships between fish occurrence and both channel unit complex- and reach-scale variables. Stream fishes were more likely to occur in larger or deeper channel unit complexes. Fish occurrence was also associated with different levels of reach-scale groundwater contribution, bankfull width-to-depth ratio, and percent instream cover. Ten fishes, typically associated with warmer water temperatures, had lower occurrence probabilities in reaches with higher groundwater contribution, whereas Banded Sculpin Cottus carolinae and Creek Chub Semotilus atromaculatus occurrence probabilities were higher. There was no relationship between occurrence probabilities and instream cover for 11 fishes. The occurrence probabilities in relation to varying amounts of instream cover for the other nine stream fishes was dependent on bankfull width-to-depth ratio, where the direction and magnitude of the relationships varied among stream fishes. The variation in occurrence relationships can be attributed to thermal preferences, environmental interactions, and the use of multiple habitat types. Our findings demonstrate the multiscale nature of fish occurrence relationships and how conservation and management may benefit from considering this complexity when developing holistic instream habitat enhancement strategies.

Fine-scale movement and habitat use of a prairie stream fish assemblage.

Measuring an organism's movement and habitat use is highly dependent on the spatial and temporal scale of the study, with most studies measuring distributions once a day or at less frequent intervals. Yet, to fully understand the rates of intra- and interspecific encounters among individuals, observations at finer spatial and temporal scales might be necessary. We used passive integrated transponder tags and antenna arrays to continuously monitor habitat use and vagility of three stream minnows; southern redbelly dace Chrosomus erythrogaster, central stoneroller Campostoma anomalum, and creek chub Semotilus atromaculatus, among and within pools of an intermittent stream. Most fish remained in the pool where they were caught and released, or returned after emigrating from the pool. Despite largely remaining within the release pool, distribution among four microhabitats differed significantly over six, 4-h time periods for all three species. Vagility, the summed distance moved among antennas, differed significantly among species. Individual vagility (mday-1) increased significantly with body length for stoneroller and chub, but not dace. Some individuals moved as much as 110mday-1 within the pool, showcasing extensive movement at fine scales. Finally, we found no evidence that feeding activity changed as a result of differential habitat use over a 24-h period. Our findings indicate considerable variation in habitat use and movement occurs among species over a 24-h period. This suggests ecologists can broaden the interpretation of processes influencing community structure (e.g., resource partitioning, avoidance of predators) by quantifying species distributions across a range of spatial and temporal scales.

Susceptibility of Representative Great Lakes Fish Species to the North Carolina Strain of Spring Viremia of Carp Virus (SVCV).

Spring viremia of carp virus (SVCV) is a notifiable pathogen of the World Organization of Animal Health. Since SVCV was isolated in Lake Ontario in 2007, concern has grown about its spread in the Great Lakes basin and its potential negative impacts on fish species of importance in stock enhancement programs basinwide. The susceptibility of representative fish species from the families Cyprinidae (Fathead Minnow Pimephales promelas, Golden Shiner Notemigonus crysoleucas, Spotfin Shiner Cyprinella spiloptera, and Creek Chub Semotilus atromaculatus), Centrarchidae (Largemouth Bass Micropterus salmoides), Percidae (Walleye Sander vitreus), Salmonidae (Rainbow Trout Oncorhynchus mykiss), and Esocidae (Muskellunge Esox masquinongy) to SVCV was evaluated by experimental infection under laboratory conditions. Morbidity and mortality were recorded, and virus re-isolation, seminested reverse transcription PCR, and histopathological assessments were performed. Using intraperitoneal (i.p.) injection, Fathead Minnows and Golden Shiners were highly susceptible to SVCV (40-70% mortality). All dead or moribund and apparently healthy surviving Fathead Minnows and Golden Shiners were SVCV positive. The SVCV was also detected in challenged but healthy Spotfin Shiners (30%) and Creek Chub (5%). However, noncyprinid species exhibited no morbidity or mortality and were free of SVCV following an observation period of 30 d. In a follow-up experimental challenge, Fathead Minnows and Golden Shiners were SVCV challenged at 103 and 105 PFU/mL by means of waterborne immersion. After immersion, Fathead Minnows and Golden Shiners exhibited characteristic SVCV disease signs, but mortality was less (30% and 10% mortality, respectively) than that in fish with i.p. injections. The SVCV was detected in all mortalities and a subset of healthy Fathead Minnows and Golden Shiners. Necrotic changes were observed in the kidneys, liver, spleen, ovaries, and heart, and other histopathological lesions also occurred. These findings suggest that two of the four cyprinids tested are susceptible to SVCV-induced disease and that all four can act as potential carriers of SVCV in the Laurentian Great Lakes. Received January 11, 2017; accepted July 17, 2017.

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

Variation in fish mercury concentrations in streams of the Adirondack region, New York: A simplified screening approach using chemical metrics

Simple screening approaches for the neurotoxicant methylmercury (MeHg) in aquatic ecosystems may be helpful in risk assessments of natural resources. We explored the development of such an approach in the Adirondack Mountains of New York, USA, a region with high levels of MeHg bioaccumulation. Thirty-six perennial streams broadly representative of 1st and 2nd order streams in the region were sampled during summer low flow and analyzed for several solutes and for Hg concentrations in fish. Several landscape and chemical metrics that are typically strongly related to MeHg concentrations in aquatic biota were explored for strength of association with fish Hg concentrations. Data analyses were based on site mean length-normalized and standardized Hg concentrations (assumed to be dominantly MeHg) in whole juvenile and adult Brook Trout Salvelinus fontinalis, Creek Chub Semotilus atromaculatus, Blacknose Dace Rhinichthys atratulus, and Central Mudminnow Umbra limi, as well as on multi-species z-scores. Surprisingly, none of the landscape metrics was related significantly to regional variation in fish Hg concentrations or to z-scores across the study streams. In contrast, several chemical metrics including dissolved organic carbon (DOC) concentrations, sulfate concentrations (SO42−), pH, ultra-violet absorbance (UV254), and specific ultra-violet absorbance were significantly related to regional variation in fish Hg concentrations. A cluster analysis based on DOC, SO42−, and pH identified three distinct groups of streams: (1) high DOC, acidic streams, (2) moderate DOC, slightly acidic streams, and (3) low DOC circum-neutral streams with relatively high SO42−. Preliminary analysis indicated no significant difference in fish Hg z-scores between the moderate and high DOC groups, so these were combined for further analysis. The resulting two groups showed strong differences (p<0.001) in DOC and SO42− concentrations as well as in pH and UV254 values. Median fish z-scores were significantly higher (p=0.002) in the group of streams with higher DOC and UV254 and lower pH and SO42−. Screening values of DOC >6.9mg/L, SO42− <2.8mg/L, pH <6.6, and UV254 >0.31cm−1 were tested as thresholds to identify Adirondack stream sites likely to have higher fish Hg concentrations. By applying a combined threshold of exceedance for either pH or UV254, sites with fish Hg concentrations that exceeded a wildlife guideline of 100ng/g were correctly identified about 75% of the time among the 36 study streams. An estimate of Hg risk applied to a data set of 391 streams based on DOC concentrations showed that about 28% were likely to pose high risk to wildlife; most of these streams were located in the western Adirondacks.

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.

Fathead minnow nidovirus infects spotfin shiner Cyprinella spiloptera and golden shiner Notemigonus crysoleucas.

Since the initial isolation of the fathead minnow nidovirus (FHMNV), concerns have been raised regarding the risks it may pose to other fish species. In this study, 7 fish species resident to the Laurentian Great Lakes were challenged intraperitoneally with 2 doses of FHMNV: 102.8 and 104.8 median tissue culture infective dose (TCID(50)) ml(-1). Infected spotfin shiner Cyprinella spiloptera and golden shiner Notemigonus crysoleucas suffered morbidity and mortality during the 40 d observation period, while other species, including creek chub Semotilus atromaculatus, rainbow trout Oncorhynchus mykiss, largemouth bass Micropterus salmoides and walleye Sander vitreus, showed no clinical signs or mortality. FHMNV was re-isolated on the epithelioma papulosum cyprini cell line from the tissues of infected spotfin shiner and golden shiner, which harbored high numbers of viral RNA copies as measured by quantitative loop-mediated isothermal amplification. Infected spotfin shiner and golden shiner exhibited external petechiae, exophthalmia, oedematous kidneys, and liver pallor. Histopathological analysis revealed multifocal areas of necrosis in the kidney, spleen and liver of infected fish. Spotfin shiner and golden shiner were then infected with 2 doses of FHMNV (10(3.5) and 10(3.9) TCID(50) ml(-1)) by immersion to mimic more natural modes of infection. Spotfin shiner experienced 60% mortality at both doses, while golden shiner did not experience mortality nor develop any clinical signs following a 40 d observation period. Overall, piscivorous fish tested in this study do not seem to be at risk for infection, while cyprinids appear to vary in their susceptibility to the strain of FHMNV used in this study.

Evidence for asymmetric competition among headwater stream vertebrates

The importance of competition among stream salamanders and other stream vertebrates in headwater systems is understudied. We conducted a replicated artificial stream experiment to evaluate competitive interactions among three common vertebrates. In this experiment, we measured change in body condition of salamanders in the black-bellied dusky complex (Desmognathus quadramaculatus/folkertsi) in the presence of two different fish species, Common Creek Chub (Semotilus atromaculatus) and Coosa Darter (Etheostoma coosae). There was no statistically significant change in body condition between the control and darter present treatments. However, salamander body condition was significantly reduced in the presence of the creek chubs suggesting an asymmetric competitive interaction between those two species. While predation is often cited as a potential mechanism limiting the distribution of stream species, the role of interspecific competition may be just as vital. Overall, our results highlight that competition, and not solely predation, may explain why some stream salamanders are restricted to headwater reaches.

Fish Energy Use among Fluctuating and Constant Thermal Regimes Simulating Winter Conditions in Rivers

AbstractDuring the winter, variation in water temperature in temperate‐zone rivers is strongly influenced by the presence or absence of surface ice cover. Prior to ice formation, water temperatures can fluctuate from nighttime lows near 0°C to daytime highs near 6°C. After ice formation, temperatures remain constant near 0°C. Climate change is projected to reduce the duration of surface ice cover in aquatic ecosystems and, thus, alter winter temperature regimes. We conducted a laboratory experiment to compare fish energy use for two situations: (1) ice free conditions with diel cycling temperatures (0.2–6°C), and (2) ice cover conditions with constant low temperatures (0.5°C). We compared the response of Creek Chub Semotilus atromaculatus, representing a coolwater species, and Brook Trout Salvelinus fontinalis, representing a coldwater species, to these temperature regimes. During a 60‐d study we monitored metabolic measurements of energy use and proximate body composition of fasted fish. For Creek Chub, there was no effect of time or temperature regime on respiration rates. Ammonium excretion declined over time for Creek Chub held at the constant low temperature but remained unchanged for fish held at the cycling temperature. For Brook Trout, there was no effect of time or temperature regime on respiration or ammonium excretion. Both species showed a loss of body lipids over the 60 d but there was no difference in the rate of loss between the two temperature treatments. Thus, we were unable to detect a difference in the energy use for these species between the different thermal regimes simulating the presence or absence of surface ice cover.

Potential population and assemblage influences of non‐native trout on native nongame fish in Nebraska headwater streams

AbstractNon‐native trout are currently stocked to support recreational fisheries in headwater streams throughout Nebraska. The influence of non‐native trout introductions on native fish populations and their role in structuring fish assemblages in these systems is unknown. The objectives of this study were to determine (i) if the size structure or relative abundance of native fish differs in the presence and absence of non‐native trout, (ii) if native fish‐assemblage structure differs in the presence and absence of non‐native trout and (iii) if native fish‐assemblage structure differs across a gradient in abundances of non‐native trout. Longnose dace Rhinichthys cataractae were larger in the presence of brown trout Salmo trutta and smaller in the presence of rainbow trout Oncorhynchus mykiss compared to sites without trout. There was also a greater proportion of larger white suckers Catostomus commersonii in the presence of brown trout. Creek chub Semotilus atromaculatus and fathead minnow Pimephales promelas size structures were similar in the presence and absence of trout. Relative abundances of longnose dace, white sucker, creek chub and fathead minnow were similar in the presence and absence of trout, but there was greater distinction in native fish‐assemblage structure between sites with trout compared to sites without trout as trout abundances increased. These results suggest increased risk to native fish assemblages in sites with high abundances of trout. However, more research is needed to determine the role of non‐native trout in structuring native fish assemblages in streams, and the mechanisms through which introduced trout may influence native fish populations.

Indirect effects of asymmetrical competition among top predators determine spatial patterns of predation risk for prey

Asymmetrical interspecific competition among top predators can indirectly affect the predation risk for their prey by altering the abundance, diet, and habitat use of inferior competitors. However, the indirect effects of such biological interactions are poorly known because of the difficulties in measuring predation risk in nature. We addressed this issue by assessing the effect of asymmetrical competition among brook trout (Salvelinus fontinalis) and two superior non-piscivorous competitors, creek chub (Semotilus atromaculatus) and white sucker (Catostomus commersonii), on the predation risk of a brook trout prey, northern redbelly dace (Chrosomus eos). We determined the spatio-temporal patterns of relative predation risk of dace with tethering experiments in 11 lakes containing either only brook trout and dace (n = 5), or brook trout, dace, chub, and sucker (n = 6). The diel pattern of the relative predation risk and the overall relative predation risk of dace were not significantly different in lakes with or without brook trout competitors. However, we observed a significant shift in the relative predation risk from the lower pelagic to the upper pelagic and littoral zones in the presence of brook trout competitors. This study highlights the fact that the outcome of interactions can vary in space and that care should be used when extrapolating the results of small-scale experiments or coarse-scale estimates to the whole ecosystem.

Relationship Between Habitat Structure and the Distribution and Abundance ofPaulisentis missouriensis(Acanthocephala) in Creek ChubSemotilus atromaculatus

Paulisentis missouriensis (Acanthocephala) occurs in creek chub Semotilus atromaculatus in 2 drainages, South Fork and Turkey Creek, of the Big Nemaha River system in southeastern Nebraska, U.S.A., but not in 2 other drainages, Muddy Creek and North Fork. The present investigation tested the hypothesis that stream habitat characteristics limit P. missouriensis to the South Fork and Turkey Creek drainages. Habitat characteristics were compared between sites in drainages where the worm occurs and where it is absent, with pools being significantly larger and more closely spaced in drainages with the worm. Within Turkey Creek, where the worm is modestly abundant, metrics describing pool size were significantly correlated with abundance of P. missouriensis. However, this effect was primarily due to the influence of 1 site, and the relationship was not evident when the drainage where the worm is abundant (South Fork) was included; in these analyses, variables describing water chemistry (oxygen concentration and total water hardness) were significantly associated with abundance of P. missouriensis. Characteristics of pool habitats appear to be able to explain the absence of P. missouriensis in the Muddy Creek and North Fork drainages, but these same characteristics are not as closely associated with variation in the abundance of P. missouriensis in the South Fork and Turkey Creek drainages where the worm is found.

Intrinsic Host Factors and the Distributional Limit ofPaulisentis missouriensis(Acanthocephala) in Southeastern Nebraska, U.S.A

Paulisentis missouriensis is a common acanthocephalan parasite of creek chub (Semotilus atromaculatus) in the streams of 2 drainages (South Fork and Turkey Creek) in the Big Nemaha River system in southeastern Nebraska, U.S.A., but is absent from streams in the remaining 2 drainages (Muddy Creek and North Fork). The present investigation tested whether intrinsic host-related factors are responsible for the distributional limit of P. missouriensis in this system. Copepods and creek chub were collected from streams where the worm is absent and exposed to infective stages of P. missouriensis under laboratory conditions. In addition, creek chub from areas lacking the worm were maintained in cages in a stream where the worm is abundant. Both creek chub and copepods from streams lacking the worm became infected under laboratory and field conditions. These results reject the possibility that the cause of the abrupt distributional limit of P. missouriensis in the Big Nemaha River system is due to intrinsic host-related phenomena. Other hypotheses that could account for the distributional limit include differing transmission conditions among drainages, environmental limits on completing development, and long-term spatiotemporal factors.

Fish Passage through Culverts in Central Michigan Warmwater Streams

AbstractRoad culverts can alter stream flow, remove fish habitat, and limit fish movement. Little is known about the effects of culverts on fish movement in low‐order, low‐gradient streams in an agricultural setting. Eleven sites on first‐ and second‐order streams in central Michigan were examined for the effects of culvert type (box, bottomless box, pipe arch, and bottomless pipe arch) on fish passage in an agricultural setting. The selected culverts were not obvious barriers to fish passage as none were perched above the stream. Four reaches (two upstream and two downstream of a culvert) were sampled three times in spring, summer, and fall 2011 at each site. Mark–recapture sampling was used to observe fish movement, and the probability of fewer fish being found upstream of a culvert relative to downstream was modeled with logistic regression. Based on recapture movements, limited passage was assumed for at least one fish species during each season at a pipe arch culvert and for one species during summer at a box culvert. The best models from logistic regression revealed that culvert length had the largest effect on the proportion of Creek Chub Semotilus atromaculatus being found upstream out of the variables used. FishXing, a computer program used to predict fish passage through culverts, predicted that five culverts had passage‐limiting flows to either Western Blacknose Dace Rhinichthys obtusus or Creek Chub during at least one season. However, all culverts were predicted to have some passable flows during each season (except one culvert during one season). Results suggest that even though culverts may not be obvious barriers, fish passage can still be limited.Received November 15, 2012; accepted March 12, 2013

Reach-Scale Land Use Drives the Stress Responses of a Resident Stream Fish

Abstract To date, relatively few studies have tried to determine the practicality of using physiological information to help answer complex ecological questions and assist in conservation actions aimed at improving conditions for fish populations. In this study, the physiological stress responses of fish were evaluated in-stream between agricultural and forested stream reaches to determine whether differences in these responses can be used as tools to evaluate conservation actions. Creek chub Semotilus atromaculatus sampled directly from forested and agricultural stream segments did not show differences in a suite of physiological indicators. When given a thermal challenge in the laboratory, creek chub sampled from cooler forested stream reaches had higher cortisol levels and higher metabolic stress responses to thermal challenge than creek chub collected from warmer and more thermally variable agricultural reaches within the same stream. Despite fish from agricultural and forested stream segments having different primary and secondary stress responses, fish were able to maintain homeostasis of other physiological indicators to thermal challenge. These results demonstrate that local habitat conditions within discrete stream reaches may impact the stress responses of resident fish and provide insight into changes in community structure and the ability of tolerant fish species to persist in agricultural areas.