Muskrats (Ondatra zibethicus) are associated with marshlands throughout North America. Their impact on marsh vegetation is well documented. In recent years, research pertaining to marsh ecosystems has emphasized the role of interspersion of marsh vegetation to higher faunal diversity and productivity. Muskrats can provide a natural control of aquatic emergents if managed properly. Experimentation at Fish Springs National Wildlife Refuge, Utah, has attempted to ascertain whether vegetation-utilization index could be used for determining muskrat population levels and to evaluate the impact of muskrats on their primary food resource, Olney's bulrush (Scirpus americanus). Three known populations of muskrats were maintained within wire-mesh enclosures 0.4-0.9 ha in size. Variable length transects were used to estimate the number of grazed stems of Olney's bulrush present in an enclosure for a 5-day period. Estimated number of grazed stems was divided by muskrat-days to give an estimate of the number of grazed stems muskrat-1 day-1. A consistant relation between the known muskrat population and the number of stems grazed muskrat-1 day-1 (23 .0) was found, indicating that a valid index could be formulated using vegetation utilization data. Assessment of plant species utilization was analyzed from dietary composition obtained from stomach contents. Olney's bulrush was the most utilized food resource. Phragmites (Phragmites australis) was the most utilized resource in the absence of bulrush. The potential effects of muskrat grazing was determined using exclosures in homogeneous stands of the above vegetation. A 4x4 randomized block design with varying levels of simulated grazing was employed for monthly replications duringthe growing season for 2 years. Effect of repeated grazing was found to be highly significant for clipping rates within and between months for both years. Vegetative yield was measured as mean dry weight (g) per stem per plot. Significant differences in yield were noted among the grazing rates. Repeated grazing of emergent vegetation by muskrats can have a marked effect on the plants' ability to grow.

The objectives of the project are fourfold: (l) to determine the annual muskrat harvest in a county of southwestern Virginia; (2) to determine the economic value of the annual muskrat harvest in a county in southwestern Virginia; (3) to determine, in so far as possible, those factors which limit a greater harvest of muskrats in southwestern Virginia and; (4) to compare the economic returns from muskrat in a southwestern Virginia county with the economic returns from muskrat in an eastern Virginia county or counties, It is hoped that data obtained in this investigation will serve as bases for 18 management recommendations which might increase the annual muskrat production on Virginia streams and marshes and which might, in some measure, bring recognition to, and stress the importance of, one of our most valuable animals. / Master of Science

As the nineteenth century drew to a close, people living in coastal Louisiana noticed that local rodents called muskrats were rapidly increasing and quickly becoming pests by digging up crops and into levees. Property owners soon demanded their elimination, but to the ire of many, Louisiana officials chose to develop a market for muskrat fur and protect its supply through management laws. The state sought the cooperation of trappers in order to maintain global demand, but when nutria were released alongside the muskrat, the ecological balance of the marsh was permanently altered. Muskrats shrank back into obscurity, and trappers struggled to embrace the nutria as a substitute. This thesis will trace the Louisiana muskrat industry's development starting with its rise in the 1890s, continuing through its years as a leading furbearer, and ending with its replacement by the nutria in the 1960s.

The Locomotive Springs Migratory Waterfowl Refuge, located on the north shore of Great Salt Lake, Utah, is a state-owned area of about 12,000 acres. Six springs arise from the desert floor and flow south and south-east toward Great Salt Lake. The refuge encompasses these springs and their outflows. The area, while predominately vegetated by the Sarcobatus-Atriplex type, has 1,200 acres of open water and about 2,560 acres of marsh and stream-channel edges. The area was purchased by the State of Utah in 1934 with the express purpose of providing waterfowl hunting for the general public who could not afford to hunt on the privately owned duck clubs that encompassed much of the better waterfowl marsh areas of Great Salt Lake (Cook, 1932).

Tyrimo objektas – Tyrimo objektas yra porakanopių žvėrių populiacijos valstybiniame Praviršulio tyrelio botaniniame-zoologiniame draustinyje. Šis draustinis yra Radviliškio rajono pietinėje dalyje, priklauso III a- klimatiniam parajoniuj. Bendras draustinio plotas 3292 ha. Aukštapelkė sudaro 60% draustinio teritorijos. Darbo tikslas - nustatyti porakanopių, graužikų ir kiškiažvėrių populiacijų būklę Praviršulio tyrelio valstybiniame botaniniame – zoologiniame draustinyje. Siekiant darbo tikslo buvo iškelti tokie uždaviniai: 1. Nustatyti draustinio porakanopių, graužikų ir kiškiažvėrių rūšinę sudėtį, jų gausą bei tankį. 2. Nustatyti porakanopių žvėrių populiacijų dinamiką. 3. Nustatyti bebrų įtaką aplinkai. 4. Įvertinti elninių žvėrių žiemos ganyklų būklę. Tyrimo metodai - Lietuvos ir užsienio autorių mokslinės literatūros analizė bei sintezė, duomenų grupavimas, statistiniai metodai, grafinis vaizdavimas. Tyrimo laikotarpis apima 2008 -2009 metus. Išstudijavus lietuvių ir užsienio autorių mokslinius veikalus bei periodinę literatūrą apie medžiojamosios faunos elgseną įtakojančius veiksnius, buvo apskaičiuota žvėrių gausa, bendras tankis, ištirta žvėrių populiacijos dinamika. / Object of research – The study is the object of cloven-hoofed game populations Praviršulio public tyrelio botaniniame-zoologiniame Reserve. This reserve is Radviliškio the southern part of the district, belongs to a III-klimatiniam parajoniuj. The total area of 3292 hectares of protected. Aukštapelkė represents 60% of the protected area. 1) Purpose of the Paper – set of cloven-hoofed, rodents and kiškiažvėrių populations of the state Praviršulio tyrelio public botaniniame - zoologiniame Reserve. The goal was to raise the following tasks: 1. Set Reserve biungulates, rodents and kiškiažvėrių species composition, their abundance and density. 2. Cloven-hoofed animals to determine the dynamics of populations. 3. Set the beaver on the environment. 4. Rate cervids game winter pasture condition. Methods of research - analysis and synthesis of Lithuanian and foreign scientific literature, data grouping, statistical methods, graphical presentation. The research period is the years 2008 - 2009. After studying scientific works of Lithuanian and foreign authors and periodic literature about the factors influencing the behaviours of hunted fauna, there was determined the abundance of animals, general density, determined the dynamics of animals population.

Force dived animals undergo cardiovascular changes characterized by bradycardia, increased total peripheral resistance, and changes in blood flow distribution. Since these changes occur in decerebrated animals, the dive response must be a brainstem reflex. However, in voluntary dives, animals may show anticipatory bradycardia and may also adjust their cardiovascular responses according to anticipated dive duration, indicating suprabulbar influences upon dive responses. Studies of heart rate using telemetry have shown that there can be substantial differences in the dive response of voluntarily and force dived animals. Furthermore, some animals show a "fear bradycardia" when trapped in a stressful situation, leading some researchers to suggest that bradycardia during forced submersion is an artifact of the stress of the situation. Muskrats (Ondatra zibethica) were observed freely diving for food in an indoor tank using a video camera and VCR unit. EKG was telemetered from the animals and recorded on the audio channel of the VCR tape. Heart rate responses to voluntary dives were analyzed and compared with those from escape and forced dives. Heart rate responses were also recorded from decorticate and sham operated muskrats to elucidate the role that the cerebral cortex plays in the dive response. In all types of dives, muskrats exhibited a rapid and large bradycardia upon submergence (heart rate declined by greater than 55% of the predive heart rate). Obviously diving bradycardia in the muskrat was not due to fear or stress, but occurred as a response to submersion per se. There was no evidence of post-dive tachycardia or anticipatory immersion bradycardia. Disturbing the animal in a non-diving situation resulted in only a 13% decrease in heart rate. In intact animals voluntary, escape, and forced submergence resulted in progressively greater decreases in heart rate. Heart rate fell by 56% in voluntary dives, 65% in escape dives, and 73% in forced dives. Intensification of the bradycardia to a lower heart rate than that seen in voluntary dives was mediated by the cerebral cortex, as heart rate in decorticate muskrats in escape and forced dives did not fall below that seen in voluntary dives. This indicates that the final adjustment of dive heart rate is dependent upon an intact cerebral cortex. However, in decorticate muskrats there appeared to be a recovery of cortical function, as intensification of bradycardia in forced dives was dependent upon the time that had elapsed after surgery. This study shows that there is a cortical influence upon the cardiovascular system during diving. It also indicates that in experiments with unanesthetized animals, the degree of stress of the situation must be taken into account, as this may affect physiological responses. / Science, Faculty of / Zoology, Department of / Graduate

The influence of environmental contaminants on the muskrat population inhabiting the contaminated lower region of the Elizabeth River was studied through an analysis of contaminant burdens, physiological characteristics, and population dynamics in comparison to those of muskrat populations from a less contaminated region of the Elizabeth River (upper region) and a nearby uncontaminated river (Nansemond River). A total of 76 muskrats was collected for contaminant analysis during December 1986 - January 1987 and December 1987 - February 1988. Twenty-two of 35 carcasses analyzed for polynuclear aromatic hydrocarbons (PAHs) had detectable levels of from 1 to 6 PAH compounds. Only three muskrats from the lower region and one from the upper region of the Elizabeth River had PAH concentrations greater than 0.03 ppm dry wt (lower limit of detection). Liver DNA adduct levels were not significantly different between muskrats collected from the lower region of the Elizabeth River and muskrats collected from the Nansemond River. However, liver microsomal enzyme activity was greater in lower region Elizabeth River muskrats than in upper region Elizabeth River or Nansemond River muskrats, as indicated by significantly reduced pentobarbital sleeping times. The mean concentration of 14 PAH compounds detected in surface sediments from the lower region of the Elizabeth River (N = 10) was significantly greater than the mean concentration detected in surface sediments collected from the upper region of the Elizabeth River (N = 5) or Nansemond River (N = 5). Of 22 organochlorine compounds analyzed in 35 muskrat carcasses, dieldrin was detected in one carcass (0.25 ppm) from the lower region of the Elizabeth River, polychlorinated biphenyls were detected in two carcasses (0.66 ppm and 0.45 ppm) from the upper region of the Elizabeth River, and p,p′-DDE was detected in two carcasses (0.03 ppm each) from the upper region of the Elizabeth River and one carcass (0.03 ppm) from the Nansemond River. p,p′-DDE was detected in 5 of 10 sediment samples from the lower region and 2 of 5 sediment samples from the upper region of the Elizabeth River. p,p′-DDD was detected in 3 of 10 sediment samples from the lower region of the Elizabeth River. Twenty-seven of 33 metals analyzed were detected in muskrat kidneys and 9 of these were significantly different among the three study regions. Mean aluminum (13.19 ppm), cadmium (3.08 ppm), copper (12.85 ppm), nickel (0.50 ppm), and zinc (88.38 ppm) concentrations were greatest in lower region Elizabeth River muskrat kidneys. Mean cadmium (1.07 ppm), chromium (43.4 ppm), lead (104 ppm), tungsten (38.1 ppm), and mercury (0.50 ppm) concentrations were significantly greater in lower Elizabeth River sediment samples. Density estimates based on shore length for the lower and upper regions of the Elizabeth River were 0.86 muskrats/IOO m of shore and 1.1 muskrats/lOO m of shore, respectively in 1987. Seventy-five female muskrats had a total of 637 placental scars (x̅ = 8.49) ranging from 1 - 20. The number of placental scars per female did not differ significantly among regions. Twelve pregnant muskrats had a total of 54 fetuses (x̅ = 4.5, range = 3 - 6). Average number of litters per year was estimated to be 1.89 with births occurring primarily from April - May and in September. Results indicated that the environmental contaminants found in the lower region of the Elizabeth River have minimal influence on the muskrats from this region. Body and spleen weights were reduced but reproduction was not affected, and the muskrat density in this region appears to be stable and similar to the density in a less contaminated area. Immunological function may be depressed. / Ph. D.

Climate change is altering environmental conditions in Canada’s western arctic, including hydrology, permafrost, vegetation, and lake habitat conditions in the heterogeneous landscape of the Mackenzie Delta. The delta is an expansive alluvial plain dominated by thousands of lakes and interconnected channels that provide habitat for fish, birds, and mammals. Muskrats (Ondatra zibethicus) are a culturally important ecological indicator species found in the Delta. Throughout the 1900s, Gwich’in and Inuvialuit residents in the Delta relied heavily on the muskrat for food, fur, and culture, but as in other regions around the world, changing socioeconomic and ecological conditions are altering the land and Indigenous Peoples’ access to it. This can strongly impact communities by affecting food security, physical health, and overall wellbeing. In the first part of this thesis, I investigated the role of muskrats in the cultural traditions and land-based livelihoods of the Gwich’in and Inuvialuit residents of the Mackenzie Delta by conducting interviews and meetings with over 70 community members. Although the role of muskrats has changed over the last 100 years, muskrat harvesting continues to offer Delta residents a meaningful way to remain engaged in, perpetuate, and strengthen their cultural identity and land-based traditions among generations, and ultimately, to foster individual and community wellbeing. In the second part of this thesis, I investigated the importance of landscape connectivity and patch quality – two properties affected by climate change – on muskrat presence and distribution in the Mackenzie Delta, using remote sensing and field-based surveys of lakes with and without muskrats present in the winter. I tested multiple hypotheses about predictors of muskrat presence and biomass using a model-selection, information theoretic approach. My results show that patch quality related to specific habitat requirements is a more important driver of muskrat distribution than landscape connectivity in the Mackenzie Delta. Muskrats were more likely to occur in lakes with longer perimeters, higher amounts of edible submerged macrophyte biomass, and sediment characteristics that supported macrophyte growth. The latter two conditions are related to spring flooding regimes, which are likely to be altered by climate change. This may result in a decrease in the quality and quantity of preferred muskrat habitat in the Mackenzie Delta. My research indicates that patch quality and landscape-level processes are important for understanding species distributions in heterogeneous landscapes. / Graduate

An easy-to-use spreadsheet version of a finite difference method for progressive landslide analysis has been developed. The finite difference method was originally developed by Dr. Stig Bernander, earlier adjunct professor at Luleå University of Technology and head of the Design Department of Skanska AB in Gothenburg, Sweden.. The so called Muskrat Falls Project consists in the ongoing construction of a hydroelectric power plant in Churchill River Valley, Labrador, Canada. The site hosting the project includes a land ridge which is supposed to be used as a natural dam and thus be submitted to important water pressures. Yet, previous landslides in the area have shown that a stability analysis is worth to be carried out in order to ensure the safety of the facility. Until now, investigations have only been carried out using the traditional limit equilibrium method and related elastic-plastic theory. For the sake of simplicity, this approach does not take into account deformations outside and inside the sliding body. However, because of the soil features in Churchill River Valley and particularly its ‘deformation softening’ behavior, there is increasing evidence that the conventional analysis is not relevant in this situation. Further, when analyzing the total stability of the ridge, only a horizontal failure surface has been used and not an inclined one, which is very optimistic and rather unrealistic.. In order to provide a more reliable study, a progressive failure analysis has been performed according to the finite difference method of Dr. Stig Bernander. The development of a spreadsheet adapted to this particular problem has allowed getting quickly and easily numerical results for several cases of study and assumptions. For assumed material properties and geometries of failure, the critical load-carrying capacity is below 1000 kN/m whereas a rise of the water level with 21 m will give an increased load of Nq  = 2420 kN/m. This is more than twice of the what the ridge may stand with the assumed properties. The investigation has led to the conclusion that the situation will be risky for many combinations of soil properties if the water level is raised as high as initially planned. The investigation also shows that more material tests are necessary and that stabilization work may be needed to eliminate the risk for a landslide.

No description available.