VTechWorks Repository :: Browsing by Author "Orth, Donald J."

Browsing by Author "Orth, Donald J."

Now showing 1 - 20 of 131

Air-breathing and movement ecology of Arapaima sp. in the Amazon
Stokes, Gretchen Louise (Virginia Tech, 2017-01-30)
The annual hydrological cycle of floodplains supports fishes that are uniquely adapted to optimize resources throughout the year. Such adaptations to changing environments include air-breathing for seasonally hypoxic waters and directed movements to best utilize habitats as they become available. This study examined the environmental, temporal and body-size influences on air-breathing behavior and movement ecology of Arapaima sp., one of the most economically and ecologically significant species in the Amazon. Acoustic (n=15) and radio (n=12) telemetry was used to study the influences on air-breathing and movement ecology of arapaima in the Central Amazon. Generalized additive mixed models showed that temperature was the most influential predictor of air-breathing intervals, followed by body size. The shortest breathing intervals were associated with consecutive "aggressive" breaths while the longest breathing intervals had consecutive "calm" breaths. Generalized linear mixed models showed that flood stage was the most important predictor of residency time, directional movement, and rate of movement. Fish moved faster in the flood and dry stages than the rising and falling stages, and spent longer in one place in the rising and falling stages than the flood and dry stages. Findings of this study may be used to inform management decisions for arapaima conservation, such as protected habitat and population counts, with applications to fishes across river-floodplain ecosystems globally.
American Eel Subpopulation Characteristics in the Potomac River Drainage, Virginia
Goodwin, Kevin R. (Virginia Tech, 1999-06-23)
The demographic characteristics of American eels (Anguilla rostrata) are believed to vary with latitude and distance inland from the ocean; eels are generally thought to increase in length, age, and the proportion of females in inland and more northerly areas. Understanding this variation is necessary for the sound management of eels, but investigations into characteristics on a broad scale within drainages are scarce. Eels in the Potomac River drainage, Virginia, were sampled over a two-year period in both near-coastal and inland areas to describe characteristics in each area as well as to understand drainage-wide patterns. Inland data resulted from sampling in the Shenandoah River drainage and near-coastal data resulted from sampling tributaries to the lower Potomac River. Movement and growth were also investigated in inland areas. Eels from the Shenandoah River drainage were significantly longer (median = 763 mm TL) and older (median = 11.5) than those found in the Potomac River tributary sites (median = 142 mm TL; median = 2.0, respectively). Both total length and age increased with increasing distance inland and sex ratio shifted from varying ratios of males:females in Potomac River tributaries to all females in the Shenandoah River drainage. Movements confirmed through mark-recapture over periods ranging up to one year were short, generally <100 m, with the longest detected movement being 1.5 km. Recapture rates were low and may be due either to low sampling efficiency, long-distance movements, or a combination of these factors. Growth and 95% confidence interval from five eels recaptured after approximately one year was 43.0 +/- 29.7 mm/year. CPUE decreased with increasing distance inland, confirming information reported by others for Virginia streams.
An analysis of the contamination by and effects of highway- generated heavy metals on roadside stream ecosystems
Mudre, John M. (Virginia Polytechnic Institute and State University, 1985)
This study examined the consequences of the opening and operation of a new highway north of Richmond, Virginia with respect to contamination of the aquatic environment with heavy metals (Zn, Cd, and Pb), and the effects of these metals on the biota of roadside streams. Sixteen sites located on six small, soft-water streams that were crossed by the highway, encompassing six reference sites located upstream of the highway, six sites located directly at the highway, and four sites located downstream of the highway, were sampled over a two and a half year period, allowing both spatial and temporal analyses. Traffic densities on the highway averaged about 12,000 vehicles per day (vpd). Significant increases in the metals concentrations of sediment, benthic invertebrates, fish whole-bodies, and fish tissues (liver, kidney, and bone) were noted over the course of the study, although the increase varied in magnitude, and were not always consistent. Sediment metals concentrations followed a dynamic plateau. Fish whole-body concentrations of Cd and Pb increased steadily over the course of the study. Spot-sampling for the same parameters along another nearby, more heavily traveled highway (50,000 vpd) indicated that increases in metals concentrations in the different ecosystem components at the study streams would have been greater had there been more traffic. A number of biotic parameters were investigated to determine whether metals contamination was affecting the biological integrity of the study sites. These were: benthic macroinvertebrate diversity and density; the percentage of the aquatic insect community that was composed of chironomids; and fish community diversity, density, and biomass. Only benthos density, the percent chironomids, and fish species diversity showed changes that could be related to metals contamination. Indications from spot sampling along the more heavily traveled highway were that if more contamination had been experienced, more biotic parameters would have been disturbed, and to a larger extent. Fish community structure analyses using the Pinkham-Pearson coefficient of similarity indicated that fish community structure became increasingly altered at highway sites, and to a lesser degree downstream sites, over the study period.
Analysis of the impact of flathead catfish predation on the abundance of four centrarchid species
Barr, Brian R. (Virginia Tech, 1994-01-13)
The top piscivore in Byllesby Reservoir, a 98.6 ha hydropower impoundment in southwestern Virginia is the flathead catfish Pylodictis olivaris. The most numerically abundant fish in the reservoir are centrarchids, specifically bluegill Lepomis macrochirus, redbreast sunfish L. auritus, smallmouth bass Micropterus dolomieu, and spotted bass M. punctulatus. A bioenergetics model was used to estimate the number of age-l and older centrarchids consumed annually by the flathead catfish population. These estimates were then compared to estimated abundances of each centrarchid species (age-1 and older) in the impoundment, resulting in an estimate of predation impact.
Analysis of the Trophic Support Capacity of Smith Mountain Lake, Virginia, for Piscivorous Fish
Cyterski, Michael John (Virginia Tech, 1999-06-08)
This investigation examined the adequacy of the forage base to meet current demand of piscivores in Smith Mountain Lake, Virginia. Surplus production, or the maximum sustainable supply, of alewife (Alosa pseudoharengus) and gizzard shad (Dorosoma cepedianum) were determined using data on the biomass, growth, and mortality of each species. Mean hydroacoustic alewife biomass from 1993-1998 was 37 kg/ha and mean gizzard shad cove rotenone biomass from 1990-1997 was 112 kg/ha. Mean annual alewife surplus production was determined to be 73 kg/ha and mean annual gizzard shad surplus production totaled 146 kg/ha. Bioenergetics modeling and population density estimates were utilized to derive the annual food consumption (realized demand) of the two most popular sport fish in the system, striped bass (Morone saxatilis) and largemouth bass (Micropterus salmoides). The striped bass population consumed 46 kg/ha of alewife and 27 kg/ha of gizzard shad annually. Largemouth bass ate 9 kg/ha of alewife and 15 kg/ha of gizzard shad annually. Annual consumption by ancillary predators was estimated to be 13 kg/ha of alewife and 35 kg/ha of gizzard shad. Prey supply to predators is limited by morphology, behavior, and distribution. The cumulative effect on prey availability of these three factors, in addition to consumption by other predators, was quantified. For largemouth bass, available supply of alewife and gizzard shad exceeded demand by 20% and 53% respectively. For striped bass, available supply of gizzard shad surpassed demand by 30% but available alewife supply was only 4% greater than demand. Annual demand of all predators was 94% of total available clupeid supply. Striped bass stockings were increased by 50% in 1998 and will remain at this level in the near future. A predator-prey simulation model of alewife and striped bass populations was developed to explore the consequences of increased predator demand. This model incorporated dependencies between alewife abundance and mortality and the mortality, abundance, and growth of striped bass. Model output showed that a 50% stocking increase has a near-zero probability of increasing the mean annual number of legal and citation striped bass in Smith Mountain Lake.
Applying ecological models to positive interactions among lotic fishes: implications for population and community regulation at multiple spatial scales
Peoples, Brandon Kevin (Virginia Tech, 2015-05-06)
Positive biotic interactions such as mutualism, commensalism and facilitation are ubiquitous in nature, but historically have received considerably less research attention than negative interactions such as competition, predation and parasitism. The paucity of research on positive interactions is particularly evident in stream ecosystems and in vertebrate communities. Stream fishes clearly provide an ideal system for advancing research on positive interactions. Many minnows (Cyprinidae) of eastern North America engage in a potentially mutualistic reproductive interaction known as nest association, in which individuals of one species (nest associates) spawn in nests constructed by host species. In nest association, hosts provide unsilted gravel substrate for spawning nest associates, and increased parental care to associate broods. High associate: host egg ratios can create a dilution effect, reducing the probability that host eggs will be preyed upon by egg predators. Nest associative interactions are common, but are relatively understudied compared to other interactions among stream fishes. The goals of this study were to apply general ecological models to this novel system to (a) gain new insight into the mechanisms structuring nest associative stream fish communities, and (b) to use inference from stream fish communities to potentially expand and improve the general ecological models. These goals required completion of three objectives, including (1) examining the influence of abiotic and biotic contexts on reproductive behavior and fitness outcomes between a cyprinid host and associate, using the biological markets model to generate predictions; (2) examining the utility of the nest web framework (previously only used for cavity nesting vertebrate communities) and the stress gradient hypothesis (previously applied almost exclusively to plant communities) for predicting which associate species spawn on nests built by various nest building species, and the consequences of these choices, respectively; and (3) using two-species occupancy modeling to determine the relative influence of biotic interactions and habitat covariates on the co-occurrence of a host and two nest associates. To accomplish these goals, I conducted a large-scale experiment to manipulate presence of mutualists (Nocomis leptocephalus, host; Chrosomus oreas, associate), egg predators (biotic context) and habitat quality (abiotic context). I conducted behavioral nest observations and conducted repeated stream fish stream fish community surveys to collect demographic data. I constructed a nest web from observational data, and implemented structural equation modeling through an information-theoretic framework to identify nest web plausibility across a large spatial extent. I tested some predictions of the stress gradient hypothesis by regressing juveniles-per-nest and a metric of cyprinid community structure on a composite measure of physical stress (scaled gradients of catchment-scale agricultural land use and catchment area). I used two-species occupancy modeling to model co-occurrence of N. leptocephalus hosts and two associates, C. oreas and Clinostomus funduloides, and used an information-theoretic framework to compare hypotheses representing the importance of biotic interactions, habitat covariates or both at determining species co-occurrence. Results corroborated some (but not all) model predictions, and identified room for improvement in each of the general models. Nest associative spawning by C. oreas was not context dependent; C. oreas did not spawn in the absence of a reproductively active male N. leptocephalus at any treatment level. However, the net fitness outcome of host and associate species was mutualistic, and the interaction outcome switched from commensalistic to mutualistic with abiotic context. N. leptocephalus reproductive success was improved by C. oreas presence in less-silted habitats, but not in heavily-silted habitats. This is most likely because broods were subject to predation in both habitat types, but were also negatively affected by siltation in silted habitats. Accordingly, egg dilution by associates was not sufficient to support a mutualistic relationship in less favorable habitats. Results suggest that the biological markets model may be a useful tool for predicting fitness outcomes of nest associative mutualism, but may not be as useful for predicting the behavioral outcomes of obligate mutualisms. Future applications of the biological markets model should carefully consider species traits, specifically the degree to which trading behavior is obligate for participants. Future work with this model will yield more insight by considering highly facultative associates. Nest webs constructed from nest observational data suggested an interaction topology in which strong (nearly-obligate) associates relied most frequently on N. leptocephalus nests, and less frequently on nests constructed by Campostoma anomalum. Weak (facultative) associates were seldom associated with nests constructed by either species, and probably spawned before hosts began nesting activity. Structural equation models corroborated this topology throughout the New River basin, although some less-supported model evidence specified some nest association by weak associates. Juveniles-per-nest of strong associates responded positively to physical stress, while this metric for other cyprinid reproductive groups showed no relationship. Proportional representation of Nocomis and strong associates also increased predictably with physical stress. This study suggests that the nest web framework can be informative to systems outside the ones for which it was developed; future studies may be able to use this framework to better understand the role of habitat-modifying species in communities other than cavity nesting terrestrial vertebrates and nest associative stream fishes. This work extended the nest web framework by (a) modeling the outcomes of interactions instead of the interactions themselves, and (b) by using structural equation modeling to test nest web predictions with an information-theoretic framework. This study also suggests that the stress gradient hypothesis can be useful for understanding interaction dynamics in vertebrate communities; this represents the first direct evidence that this model can be used in vertebrate communities. Further, I demonstrate that the stress gradient hypothesis may be extended to predict community structure. However, more research in a diversity of systems will be needed to determine the extent to which this can be applied. This study provides some of the first evidence of large-scale positive co-occurrence patterns in vertebrates. However, the precise roles of habitat covariates and biotic interactions were species-specific. Occupancy results suggest that co-occurrence between N. leptocephalus and nest associate C. funduloides is driven only by reproductive behavioral interactions. Alternatively, evidence suggests that co-occurrence between N. leptocephalus and C. oreas is driven by both nest association and habitat covariates. That two-species occupancy modeling can be a useful tool for comparing difficult-to-test hypotheses involving biotic interactions at large spatial scales. This study represents the first quantitative, multi-scale treatment of positive interactions in stream ecosystems. This study demonstrates that applying general ecological models to stream fish communities can yield new insights about both the study system and the models themselves. While models of negative interactions, food webs and dispersal have been applied to stream fishes, we stand to gain much ground by also considering positive biotic interactions. In doing so, stream fish ecologists will also be able to contribute to the advancement of general ecology, and thus raise awareness for these understudied ecosystems and taxa.
Are Road Crossings Fragmenting Populations of Clinch Dace?
Bourquin, Rebecca M.; Orth, Donald J.; Hallerman, Eric M.; Stauffer, Dean F. (Humboldt Field Research Institute, 2020-11-16)
Chrosomus sp. cf. saylori (Clinch Dace) is a newly recognized species of minnow with a restricted distribution in southwestern Virginia. We analyzed genetic variation and abundance at paired sites above and below road crossings. Road crossings did not have a strong effect on presence, abundance, or genetic differentiation of Clinch Dace. Of all sites where Clinch Dace were found, only 1 perched culvert presented a barrier to upstream migration; however, no genetic differentiation was found between collections above and below that or any other culvert. Distribution and abundance of Clinch Dace populations were not influenced by habitat variables measured at the site level. Low abundance in small headwaters, nest association, and high mobility appear to be characteristics of this species of Chrosomus.
Assessing potential navigation impacts to the Kanawha river ecosystem: a modeling approach
Hershfeld, Donald Christopher (Virginia Tech, 1987-12-05)
An extensive study of the biota of the Kanawha River was integrated to examine the trophic basis of fish production and predict potential impacts of increased tow traffic at two sites in the Winfield Pool. Total standing stock and production of adult fish were estimated as 242 kg/ha and 188 kg/ha/yr, respectively. Sixtyâ one species were categorized into six trophic groups. Trophic generalists (omnivores and herbivore/detritivores) consumed a variety of foods including considerable detritus. These groups accounted for 73 to 83% of total ichthyomass and 81% of total adult production. Total fish consumption at the more riverine upper site was partitioned into 35% l detritus, 28% invertebrates, 20% plant matter, 12% other fish, and 5% crayfish. At the lower, more lentic site the diet consisted of 34% detritus, 25% plant matter, 21% other fish, 17% invertebrates, and 3% crayfish. The overall basis of production relies upon imports of allochthonous materials.
Assessing predictive performance and transferability of species distribution models for freshwater fish in the United States
Huang, Jian (Virginia Tech, 2015-05-27)
Rigorous modeling of the spatial species distributions is critical in biogeography, conservation, resource management, and assessment of climate change. The goal of chapter 2 of this dissertation was to evaluate the potential of using historical samples to develop high-resolution species distribution models (SDMs) of stream fishes of the United States. I explored the spatial transferability and temporal transferability of stream–fish distribution models in chapter 3 and chapter 4 respectively. Chapter 2 showed that the discrimination power of SDMs for 76 non-game fish species depended on data quality, species' rarity, statistical modeling technique, and incorporation of spatial autocorrelation. The area under the Receiver-Operating-Characteristic curve (AUC) in the cross validation tended to be higher in the logistic regression and boosted regression trees (BRT) than the presence-only MaxEnt models. AUC in the cross validation was also higher for species with large geographic ranges and small local populations. Species prevalence affected discrimination power in the model training but not in the validation. In chapter 3, spatial transferability of SDMs was low for over 70% of the 21 species examined. Only 24% of logistic regression, 12% of BRT, and 16% of MaxEnt had AUC > 0.6 in the spatial transfers. Friedman's rank sum test showed that there was no significant difference in the performance of the three modeling techniques. Spatial transferability could be improved by using spatial logistic regression under Lasso regularization in the training of SDMs and by matching the range and location of predictor variables between training and transfer regions. In chapter 4, testing of temporal SDM transfer on independent samples resulted in discrimination power of the moderate to good range, with AUC > 0.6 for 80% of species in all three types of models. Most cool water species had good temporal transferability. However, biases and misspecified spread occurred frequently in the temporal model transfers. To reduce under- or over-estimation bias, I suggest rescaling the predicted probability of species presence to ordinal ranks. To mitigate inappropriate spread of predictions in the climate change scenarios, I recommended to use large training datasets with good coverage of environmental gradients, and fine-tune predictor variables with regularization and cross validation.
Assessment of the performance of stocked northern and Florida largemouth bass and their progeny in Briery Creek Lake, Virginia
Hoover, Randall S. (Virginia Tech, 1992-02-05)
This study examined the suitability of Florida largemouth bass (Micropterus salmoides floridanus) for introduction into Virginia and other mid-latitude waters by comparing the performance of northern (M. s. salmoides), Florida, and hybrid largemouth bass in a 342 ha south-central Virginia reservoir, Briery Creek Lake (BcL). Fingerling northern and Florida largemouth bass were stocked into Briery Creek Lake in 1986, following impoundment, and in 1987. Largemouth bass were collected for genotypic and performance analyses in the autumn and spring beginning in 1989 and ending spring 1991. Electrophoretic analyses demonstrated that hybrid largemouth bass (F1 and Fx) dominated the 1987-1990 cohorts and indicated that one or both founding stocks were genetically impure. Comparisons of electroshock catch composition showed no survival advantage for Florida largemouth bass (FLMB) age-1 and older and no differential vulnerability to angling among the four presumptive genotypes of largemouth bass in Briery Creek Lake. Age-O FLMB proportions declined over both winters (1989-1990 and 1990-1991) indicating relatively high first-mortality in the thermal regime of Briery Creek Lake (3,875 annual mean of heating degree days). Statistical comparisons of growth revealed no consistent differences among the respective bass genotypes, although survival and growth tended to be slightly higher for PI hybrid bass. The average total length of largemouth bass in BCL was below the state's average by age three. Total lengths of age-O FI and northern largemouth bass (NLMB) were higher than FLMB and Fx bass in October, perhaps as a result of earlier spawning among NLMB and between the subspecies. Relative weights of largemouth bass in BCL were generally below 95; and few significant differences in (Wr) were observed among the presumptive largemouth bass genotypes. The suboptimal condition (Wr) of largemouth bass in BCL coupled with the decline in growth and condition of bass with increasing age suggested inadequate prey abundance in Briery Creek Lake. Overall, Florida subspecific alleles did not increase in BCL over time, but the population genetic composition shifted toward an Fx mixture in the 1990 year class; future generations of largemouth bass should be dominated by Fx individuals. Results of this study did not demonstrate substantial performance differences among northern and Florida largemouth bass, and their hybrids, except for poorer first-year survival of the Florida subspecies. Therefore, this study provides no support for the continued introduction of Florida largemouth bass in Virginia or other mid-latitude regions.
Assessment of the Response of Piscivorous Sportfishes to the Establishment of Gizzard Shad in Claytor Lake, Virginia
Bonds, Charles Craig (Virginia Tech, 2000-02-07)
Gizzard shad were illegally introduced to Claytor Lake in the late 1980s and soon established a thriving population. This study assessed 1) the degree to which gizzard shad were utilized by piscivores (pelagic - striped bass Morone saxatilis, hybrid striped bass M. chrysops x M. saxatilis, and walleye Stizostedion vitreum, and three littoral black basses Micropterus spp.), 2) the availability of gizzard shad as potential prey as determined from age and growth analysis, and 3) the performance (growth rates, relative weight, and relative abundance) of piscivores before versus after gizzard shad establishment. Gizzard shad were more highly utilized by pelagic predators (especially striped bass and their hybrids) than black basses. Rapid growth of gizzard shad (mean back-calculated length at age-1 = 155 mm TL) meant that almost all morphologically available shad were age-0. The reliance on one edible age class of gizzard shad resulted in an unstable food supply as evidenced by much greater striped bass shad consumption in Summer 1998 (63 % by weight) when age-0 shad were more abundant than in Summer 1997 (7 % by weight). Striped bass was the only species to exhibit faster growth rates and mean relative weight (Wr) values in the 1990s versus pre-shad years. Walleye (except age-1) and black bass growth rates declined, and mean Wr values either remained consistent or declined. Largemouth bass and walleye were the only sportfish to show increases in relative abundance. Benefits of gizzard shad as a forage fish appear to be limited to striped bass and its hybrid species. It is possible that gizzard shad have had, directly or indirectly, an adverse impact on the black basses of Claytor Lake, but explanatory analysis of these relationships was beyond the scope of this study.
An assessment of the transferability of habitat suitability criteria for smallmouth bass
Groshens, Thomas P.; Orth, Donald J. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1993-06)
An assessment of the transferability of habitat suitability criteria for smallmouth bass, Micropterus dolomieu
Groshens, Thomas P. (Virginia Tech, 1993-01-05)
The purpose of this study was to determine if habitat suitability criteria developed in the summer months for sma11mouth bass were transferable among streams representing different eco regions. Habitat suitability criteria were developed for depth, mean column velocity, cover and substrate for two size classes of sma1lmouth bass, 100-199mm and >200mm, in the North Anna River and Craig Creek, Virginia. Criteria that accurately describe habitat selection by a species or guild in a system different from where the criteria were developed are said to be transferable to that system. The transferability of suitability criteria between the North Anna River and Craig Creek, as well as depth and velocity criteria from Minnesota, the Huron River, Michigan and the Upper James River, Virginia, to the North Anna River and Craig Creek were tested using a 2x2 contingency table analysis. Depth criteria for the smaller sizes of sma1lmouth bass did not transfer well between regions; 4 of the 8 transferability tests (50%) failed. Depth criteria for larger sma1lmouth bass transferred to the North Anna River and Craig Creek in all cases. Velocity criteria developed for the smaller size classes did not transfer well among regions; only 3 of the 8 transferability tests were positive. Likewise, velocity criteria for larger sizes of smallmouth bass did not transfer well; only 1 of 8 tests were positive. General criteria were developed for depth and mean column velocity by averaging the suitability values reported from this and 3 other studies. General depth and velocity criteria transferred well to the North Anna River and Craig Creek for both the larger and smaller size classes of smallmouth bass; all depth tests were positive and 3 of 4 velocity tests were positive. The improved success of transferability warrants investigation of developing general criteria for smallmouth bass. Cover criteria for both size classes of smallmouth bass were transferable from the North Anna River to Craig Creek but not vice versa. Substrate heterogeneity criteria were not transferable between the North Anna River and Craig Creek for either size class of smallmouth bass. Criteria developed for the percentage of substrate particles >15cm (smallmouth bass >200mm only) were transferable from Craig Creek to the North Anna River but not vice versa. The transferability of habitat suitability criteria among regions was inconsistent and it is recommended that site-specific criteria be developed for each stream to which habitat assessments are applied. Additionally, nose velocities used were more consistent between the North Anna River and Craig Creek than were mean column velocities used. Hence, it is recommended that information on nose (focal point) velocities be incorporated into habitat studies to more accurately describe smallmouth bass velocity requirements.
Bald eagle distribution, abundance, roost use and response to human activity on the northern Chesapeake Bay, Maryland
Buehler, David A. (Virginia Tech, 1990-01-11)
I studied bald eagle (Haliaeetus leucocephalus) distribution, abundance, roost use and response to human activity on the northern Chesapeake Bay from 1984-89. The eagle population consisted of Chesapeake breeding eagles, Chesapeake nonbreeding eagles, northern-origin eagles and southern-origin eagles; changes in overall eagle distribution and abundance reflected the net changes in these 4 groups. Breeding territories on the northern Chesapeake increased from 12 to 28 from 1984 to 1988. Breeding eagles were resident all year, always ~7 km from the nest. Chesapeake nonbreeding eagles moved throughout most of the bay, but rarely left it (~5% of the radio-tagged eagles were off the bay during any month). Northern eagles migrated into the bay in late fall (x = 21 December! n = 7! range = 61 days) and departed in early spring (x = 27 March, n = 14, range = 43 days). Southern eagles arrived on the northern bay throughout April-August (x = 6 June, n = 11, range = 94 days) and departed from June - October (x = 3 September, n = 22, range = 119 days). Northern Chesapeake eagle abundance peaked twice annually; in winter (261 eagles, December 1987), driven by the presence of northern eagles, and in summer (604 eagles, August 1988), driven by the presence of southern birds. Of 1,117 radio-tagged eagle locations, only 55 (4.90/0) occurred in human-developed habitat, which composed 27.7% of 1,442 km2 of potential eagle habitat on the northern Chesapeake Bay (P < 0.001). During 36 aerial shoreline surveys, eagles were observed on only 111 of 700 (15.9%) 250-m shoreline segments that had development within 100 m, whereas eagles were observed on 312 of 859 (36.30/0) segments when development was absent (P < 0.001). On average, eagles were observed on 1.0 segment/survey that had coincident pedestrian use within 500 m, compared to 3.6 segments/survey expected if eagles and pedestrians were distributed along the shoreline independently (n = 34 surveys, P < 0.001).
Biological and Ecological Trait Associations and Analysis of Spatial and Intraspecific Variation in Fish Traits
Henebry, Michael Lee (Virginia Tech, 2011-06-07)
Traits provide an informative approach to examine species-environment interactions. Often, species-by-species approaches are inefficient to generate generalizable ecological relationships and do not predict species responses to environmental changes based on specific traits species possess. Multiple lines of inquiry and multi-scale approaches are best for assessing environment-trait responses. This thesis examines important questions not specifically addressed before in traits-based research. Chapter one explores biological and ecological trait associations incorporating ontogenetic diet shifts for New River fishes. Niche shift analysis as a chapter one sub-objective quantitatively support where species-specific diet shifts likely occur. Strong biological-ecological trait associations, some intuitive and others not so intuitive, were found that relate biological structure to ecological function. Improved understanding of trait associations, including what factors influence others, supports inference of ecology of fishes. Chapters two and three examine spatial and intraspecific trait variability. Chapter two specifically examines large-scale life history trait variability along latitudinal gradients for twelve widely distributed fish species, including directionality of trait variation, and hypothesizing how optimal traits change with large-scale environmental factors. Strong positive and negative patterns found include average total length of newly hatched larvae, average total length at maturation, average spawning temperature, average egg diameter, and maximum length. These five traits are correlated with other adaptive attributes (i.e. growth rate, reproductive output, and longevity/population turnover rate). In contrast to latitudinal scale, Chapter three examines trait variability of white sucker (Catostomus commersonii) and fantail darter (Etheostoma flabellare) as a function of small-watershed scale spatial factors and anthropogenic disturbance. Toms Creek and Chestnut Creek white sucker and fantail darter displayed positive response to disturbance, contrary to past studies. Lower resource competition, and / or competitive exclusion of fishes with similar niche requirements are possible mechanisms. All three objectives support understanding of trait association and variability as a useful foundation in ecological applications and for formulating plans for conservation and management of species.
Biological Surveys for Fries Hydroelectric Project in the Upper New River, Grayson County, Virginia
Carey, Caitlin; Orth, Donald J.; Emrick, Verl III (FERC, 2018-04)
Operated by Aquenergy Systems, LLC (the Licensee; a subsidiary of Enel Green Power North America, Inc.) and licensed by the Federal Energy Regulatory Commission (FERC), the Fries Hydroelectric Project (the Project; FERC No. 2883) is currently undergoing relicensing using FERC’s Traditional Licensing Process (TLP). The current license for the Project was issued June 10th, 1980 and is set to expire May 31st, 2020. In compliance with the first stage of FERC’s TLP, the Licensee filed its Notice of Intent (NOI) and Pre-Application Document (PAD) with FERC (May 2015; Aquenergy Systems, LLC 2015), conducted a joint meeting and site visit with resource agencies and members of the public to solicit input on information needs and study plans (September 2015), and received written comments from stakeholders identifying information gaps and necessary studies to be performed. Pursuant to input provided from resource agencies and the public, the Licensee prepared and distributed a draft outline of proposed studies and methodology to agencies on March 18, 2016. The Licensee held a follow-up joint agency conference call (March 24th, 2016) to receive feedback on the proposed study plans and to reach an agreement on all reasonable and necessary studies as requested by the agencies. Agency comments and changes were incorporated into study plans and a revised outline was distributed to the agencies on April 15th, 2016...
Channel Morphology and Riparian Vegetation Influences on Fluvial Aquatic Habitat
Kozarek, Jessica Lindberg (Virginia Tech, 2011-01-14)
As public awareness of river degradation has grown in recent years, the number of stream restoration activities has increased dramatically. Anthropogenic influences at a range of spatial scales from watershed landuse to riparian vegetation management to local channel morphology can have hierarchical relationships to local (meso- and macro-) in-stream habitat characteristics. This research examined these influences first by examining the influence of complex channel morphology on meso-scale brook trout (Salvelinus fontinalis) habitat in Shenandoah National Park, VA, and then by examining the combined influence of watershed urbanization and riparian vegetation (100-200 m reaches) on stream temperature. Moving beyond one-dimensional (1D) averaged representations of fish habitat, this research explored the distribution of two-dimensional (2D) flow complexity metrics at the meso-habitat scale as explanatory variables for brook trout habitat preferences and as potential metrics to evaluate habitat restoration design. Spatial hydraulic complexity metrics, including area-weighted circulation and kinetic energy gradients, were calculated based on 2D depth averaged modeled velocity distributions in two 100-m reaches on the Staunton River. While there were no statistically significant correlations between kinetic energy gradients or area-weighted circulation and fish density, fish density was positively correlated to the percent of the channel dominated by protruding boulders. The structural complexity of areas with protruding boulders create complex flow patterns suggesting that flow complexity plays an important role in available brook trout habitat preferences at the local scale, although the 2D depth averaged model may not have adequately represented this complexity. The 2D distribution of flow characteristics was then investigated further to quantify areas of flow refugia (low velocity shelters) and the relationship between these areas, traditional measures of habitat quality, and fish biomass. Flow complexity in the vicinity of flow obstructions (in this case, boulders) was investigated further using patch classification and landscape ecology metrics. The relative influence of riparian vegetation on stream temperature (another important habitat characteristic) in urban and nonurban watersheds was investigated in 27 paired forested and nonforested reaches in PA, MD, and DE. Riparian vegetation and watershed-scale urbanization both influence stream temperature, which can have profound impacts on in-stream ecosystems. Generally, increased urbanization and removal of riparian forest influenced maximum stream temperatures resulting in higher maximum summer stream temperatures (up to 1.8°C); however, the influence of riparian forests (at at 100-200 m reach scale) decreased with increasing urbanization. Extreme maximum summer temperatures, which are a concern for aquatic biota, increased in both frequency and duration in urban nonforested reaches relative to forested reaches indicating that the addition of a forested 100-200 m long buffer partially mitigated these temperature extremes even in urban watersheds. Overall, changes to channel morphology and riparian vegetation had measurable local effects on stream habitat (temperature and hydraulic complexity) yet the implications of restoration efforts at the local scale on ecosystem services at a larger (km +) scale requires further study.
Characterization of pond effluents and biological and physicochemical assessment of receiving waters in Ghana
Ansah, Yaw Boamah (Virginia Tech, 2010-04-09)
This study was carried out to characterize ponds and aquaculture systems, and also to determine both the potential and actual impacts of pond aquaculture effluents on receiving stream quality in the Ashanti and Brong Ahafo regions of Ghana. Water, fish and macroinvertebrate samples were collected from upstream, downstream and nearby reference streams of, and questionnaires administered to, 32 farms. Total settleable solids were higher in ponds than reference streams (p = 0.0166); suspended solids was higher in ponds than reference streams (p = 0.0159) and upstream (p = 0.0361); and total phosphorus was higher in ponds than reference (p = 0.0274) and upstream (p = 0.0269). Total nitrogen was most clearly higher in ponds than all other locations: p = 0.0016, 0.0086 and 0.0154 for the differences between ponds and reference, upstream, and downstream respectively. BOD5 level was also higher in ponds than all locations (p = 0.0048, 0.0009, and 0.0012 respectively). Also, non-guarding fish species were more abundant in reference streams than downstream (p = 0.0214) and upstream (p = 0.0251), and sand-detritus spawning fish were less predominant in reference streams than upstream (p = 0.0222) and marginally less in downstream locations (p = 0.0539). A possible subsidy-stress response within study streams was also observed. Hence, ponds are potential sources of these water quality variables to receiving streams. Effluent-receiving streams, generally, were not much different from reference streams in terms of most the metrics of community structure and function used in the comparisons. Hence, even though receiving streams in Central Ghana may not be severely impacted by aquaculture effluents at the moment, the management of pond effluents will determine the scale of future impact. Vegetable, cereal, and livestock farming could serve as additional sources of fecal streptococci and coliform bacteria and nutrient-enrichment within the study area, besides aquaculture, and so these industries must also be included in efforts to minimize pollution of these streams.
Characterization of the molecular genetic variation in wild and farmed Nile tilapia Oreochromis niloticus in Ghana for conservation and aquaculture development
Anane-Taabeah, Gifty (Virginia Tech, 2019-02-01)
The Nile tilapia Oreochromis niloticus is native to Africa and middle East, and is an important source of nutrition for many in sub-Saharan Africa. Understanding the genetic diversity within and differentiation among wild populations can help identify O. niloticus populations that are imperiled and require directed management, especially because of increasing threats to the species' long-term persistence in the wild, including habitat destruction, overfishing, climate change, and hybridization with farmed populations. Knowledge of the genetic variation among wild populations also can contribute to foundation and selection of genetically diverse populations for aquaculture. I assessed the genetic variation among tilapia populations using fin-clips collected between December 2014 and July 2017 from 14 farmed sources, mostly originating from cage farms on the Volta Lake, and 13 wild sources from nine river basins in Ghana. I also conducted a laboratory growth experiment in Ghana with two wild populations to evaluate the tolerance of different genotypes to high temperatures, to inform their development for aquaculture in West Africa. I found that pure O. niloticus populations persist in the wild but some have been extensively introgressed with the closely related species, O. aureus, which has not previously been documented in Ghana. Additionally, some wild populations appear to have recently declined significantly in numbers, likely due to overfishing and habitat modification, the latter primarily as a result of illegal alluvial mining ongoing in Ghana. Analysis of the farmed populations revealed that at least two farms were growing the unapproved genetically improved farmed tilapia (GIFT) and related strains, and that escaped individuals are admixed into some wild populations. The results of my laboratory experiment showed that O. niloticus populations occurring in northern Ghana already may be adapted to warmer temperatures and could be developed and used purposefully in aquaculture, taking advantage of their adaptation. To protect remnant pure O. niloticus populations in the wild, timely conservation decisions should be made and implemented. Protecting wild O. niloticus populations also would ensure that pure germplasms are available to develop aquaculture stocks from native populations.
Characterizing a Hidden Fishery: Setline Fishing in the New River, Virginia
Dickinson, Benjamin David (Virginia Tech, 2013-12-19)
Catfishes Ictaluridae are important food fish that are harvested from the New River, Virginia by multiple methods, yet standard creel survey approaches do not accurately sample setline effort, a popular fishing gear for catfish. I characterized the New River setline fishery by estimating setline effort and catch rates of catfish and by-catch in 2011, and by investigating the attitudes and opinions of setline users during 2012. Setline effort was highest during June-August, and declined significantly by mid-September. Several dedicated setline users accounted for a significant portion of total setline effort. Experimental setlines baited with live minnows Cyprinidae proved to be an effective method for catching catfish but caught few walleye Sander vitreus, smallmouth bass Micropterus dolomieu, and muskellunge Esox masquinongy. Estimated by-catch of these species by setline fishers is small compared to catch by hook-and-line anglers, though walleye experienced high setline hooking mortality, and catch rates increased in autumn months. Setlines appear to be part of a larger "way of life" for some rural individuals, who may also hunt, trap, and garden as part of activities to supplement their diet or income. New River setline fishers strongly believe that setline fishing has declined significantly in the New River Valley due to improving socioeconomic status of the region, changing recreational values (such as focus on catch-and-release fishing and paddle sports), increasing recreational traffic and law enforcement presence, and decreasing participation in setline fishing by younger generation.

Browsing by Author "Orth, Donald J."

Results Per Page

Sort Options