Theses and Dissertations at Montana State University (MSU)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/732
Browse
5 results
Search Results
Item Success of westslope cutthroat trout and arctic grayling conservation translocations in Yellowstone National Park, Montana and Wyoming, USA(Montana State University - Bozeman, College of Letters & Science, 2021) Puchany, Andriana Rachel; Chairperson, Graduate Committee: Alexander V. ZaleRestoration of native Westslope Cutthroat Trout Oncorhynchus clarkii lewisi and fluvial Arctic Grayling Thymallus arcticus in Yellowstone National Park is a high priority for fishery managers. Restoration of the East Fork Specimen Creek and Grayling Creek watersheds included construction of fish barriers to isolate watersheds, application of rotenone to eliminate nonnative and hybridized fish, and translocations of native fish. We sampled these watersheds in 2018 and 2019 to evaluate the success of restoration efforts by 1) estimating the stage of recovery achieved by translocated populations, 2) determining contributions of Westslope Cutthroat Trout donor sources to the translocated populations in the East Fork Specimen Creek watershed by investigating their genetic ancestries, and 3) making comparisons of recovery between the East Fork Specimen and Grayling Creek watersheds. Recovery of Westslope Cutthroat Trout in both watersheds is progressing, with expected differences in stage of recovery between the two watersheds attributable to a 5-year difference in restoration timelines. Conversely, recovery of Arctic Grayling in Grayling Creek appears improbable without management intervention, but the surprising documentation of naturally reproduced individuals engenders a hopeful future for continued Arctic Grayling recovery efforts. Interspecific hybrid introgression discovered in Westslope Cutthroat Trout populations in East Fork Specimen and Grayling creeks probably resulted from barrier failure or incomplete eradication of hybrid fish during rotenone treatments. Whereas all Westslope Cutthroat Trout donor sources contributed to the recovering population in East Fork Specimen Creek, contributions were disproportionate to numbers translocated, indicating potential fitness differences among donor sources. Findings from this study have already helped Yellowstone National Park fishery managers make adaptive management decisions and will help inform future native fish conservation translocations.Item Evaluation of embryo suppression methods for nonnative lake trout in Yellowstone Lake, Yellowstone National Park, Wyoming, USA(Montana State University - Bozeman, College of Letters & Science, 2019) Poole, Alex Stephen; Chairperson, Graduate Committee: Alexander V. ZaleIntroduced Lake Trout Salvelinus namaycush threaten native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in Yellowstone Lake, Yellowstone National Park. Gill nets have been used to suppress subadult and adult Lake Trout since 1995. Because survival of embryonic and larval life history stages can have profound effects on population dynamics of Lake Trout, suppression at those stages, especially if used in concert with intensive gill netting of older fish, could enhance suppression efforts. Therefore, I conducted controlled laboratory and field experiments to systematically evaluate the effects of a variety of candidate chemical (sodium chloride, calcium carbonate, gelatin, and liquid and powdered rotenone), biological (carcass and carcass analog), and physical (sediment) suppression methods on different developmental stages of Lake Trout embryos and larvae. Liquid and powdered rotenone applications, fish carcass and carcass analog exposures, and sediment deposition significantly increased embryo mortality in laboratory experiments. Sodium chloride, calcium carbonate, and gelatin applications were not effective. In-situ exposure to ground carcass material in Yellowstone Lake resulted in 100% embryo mortality in 14 and 28 kg/m 2 biomass treatments; sediment deposition caused 97% embryo mortality among overwintering incubators. Embryo mortality was probably caused by hypoxic conditions within substrates. Embryo suppression methods differed in their effectiveness, rate at which mortality was achieved, and ease of application. These differences, as well as Lake Trout spawning site characteristics such as depth, contour, fetch, substrate size, interstitial depth, isolation, and presence of non-target organisms ultimately determine which embryo suppression method will be most applicable in a given situation. Nevertheless, implementation of successful embryo suppression techniques evaluated in this study could be used to increase mortality of Lake Trout in Yellowstone Lake. Incorporating effective embryo suppression in an Integrated Pest Management approach has the potential to provide more effective Lake Trout suppression in the long term.Item Quantifying the spatial structure of invasive lake trout in Yellowstone Lake to improve suppression efficacy(Montana State University - Bozeman, College of Letters & Science, 2019) Williams, Jacob Robert; Chairperson, Graduate Committee: Christopher S. GuyConserving Yellowstone Cutthroat Trout by suppressing invasive Lake Trout in Yellowstone Lake is a high priority for Yellowstone National Park natural-resource managers. Insight into the spatial structure of Lake Trout throughout the lake will help increase the efficacy of the Lake Trout suppression program. Lake Trout (N = 578) were surgically implanted with dual acoustic and radio transmitters from 2015 through 2017. Mobile acoustic (boat) and radio (fixed-wing aircraft) telemetry surveys were performed to identify aggregations of Lake Trout. Telemetry surveys occurred during the spawning period (autumn) in 2016 and during the summer and spawning period in 2017. Lake Trout exhibited distinct aggregations during the summer and spawning period. Lake Trout aggregated at nine locations during the summer 2017 and were most frequently located in the West Thumb. Lake Trout aggregated at 22 locations during the spawning period including 12 previously undocumented putative spawning locations. Two aggregations in the West Thumb, Carrington Island and Anglers Bluff, had the highest relative densities of Lake Trout. Aggregations during the summer were generally farther from shore, greater in depth, and more dispersed than aggregations during the spawning period. Targeting locations of Lake Trout, as identified through telemetry, with gill nets was an effective strategy for increasing catch-per-unit-effort. The Lake Trout suppression program is probably altering the behavior of Lake Trout in Yellowstone Lake, which explains the high number of spawning locations and low spawning site fidelity relative to other research studies on Lake Trout spawning behavior. This study provided valuable insight into the spatial structure of Lake Trout in Yellowstone Lake. The areas Lake Trout aggregated will continue to be targeted by gillnetting and novel embryo suppression methods.Item Assessment of an invasive lake trout population in Swan Lake, Montana(Montana State University - Bozeman, College of Letters & Science, 2010) Cox, Benjamin Samuel; Chairperson, Graduate Committee: Christopher S. GuyThe recent invasion of lake trout into the Swan River drainage in Northwest Montana threatens one of the last remaining recreational bull trout fisheries in the USA. An inter-agency group is implementing an experimental lake trout suppression program on Swan Lake. The objectives of this study were to establish a baseline data set on the lake trout population in Swan Lake concurrently with the experimental removal effort, simulate alternative management scenarios using matrix models and identify spawning locations of lake trout to target adult fish and embryos. A commercial gill-net sampling effort provided data to estimate abundance, size structure, age structure, growth, condition, maturity, fecundity, and mortality of lake trout in Swan Lake. Lake trout in Swan Lake grew rapidly, attained large sizes, and were in high condition. The size and age structure of lake trout sampled was skewed towards juvenile lake trout, indicating the population was growing rapidly. Matrix-model simulations also indicated the lake trout population would continue to grow with no suppression efforts, but suppression efforts could reduce the population growth rate. Population growth was particularly sensitive to changes in age-0 survival in population models. Elasticity analysis of matrix simulations indicated survival from birth to sexual maturity, followed by survival of adult fish contributed most to population growth. Lake trout spawning locations were identified using ultrasonic telemetry, short-set gill nets, and in-situ egg nets. Spawning locations identified with acoustic telemetry were confirmed by capturing gravid lake trout in gill nets and lake trout eggs in the substrate. These results suggest that the inter-agency group should focus removal efforts on sub-adult and adult lake trout at if extirpation of the population is the goal. Given the uncertainty in the vital rates and the potential bias in exploitation rates used to model suppression scenarios, annual suppression efforts should be increased from the 2008 level to ensure a decline in the lake trout population.Item Demography of lake trout in relation to population suppression in Yellowstone Lake, Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2010) Syslo, John Michael; Chairperson, Graduate Committee: Christopher S. GuyIntroduced lake trout Salvelinus namaycush threaten to extirpate native Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri in Yellowstone Lake, Yellowstone National Park. Suppression of the lake trout population is deemed necessary for the conservation of Yellowstone cutthroat trout. A National Park Service gill netting program removed nearly 273,000 lake trout from Yellowstone Lake between 1995 and 2007. Lake trout population size has not been estimated; therefore, it is difficult to determine the efficacy of the program (i.e., proportion of the population that has been removed). My objectives were to (1) examine catch per unit effort (C/f) through time and catch as a function of effort to determine if the suppression program has caused lake trout abundance to decline, (2) determine if length structure, age structure, individual growth, mortality, body condition, length at maturity, age at maturity, and fecundity have changed as a function of harvest, and (3) develop age-structured models to determine the level of mortality required to cause population growth rate to decline below 1.0 (replacement). An increase in lake trout abundance was indicated by increasing C/f over time. Additionally, catch has continued to increase as a function of effort, indicating lake trout abundance is increasing. Population metrics were not clearly indicative of a response to harvest. However, metrics were comparable to North American lake trout populations where harvest has occurred, indicating that lake trout have not reached carrying capacity in Yellowstone Lake. Results from an age-structured matrix model determined the rate of population growth was 1.1 given the current rate of fishing mortality and that population growth rate would be 1.3 in the absence of fishing mortality. The current rate of population growth is positive; however, it is slower than it would be in the absence of lake trout suppression. Fishing mortality needs to increase from the rate of 0.22 estimated in 2007 to at least 0.32 to reduce population growth rate below replacement. Lake trout suppression is becoming an increasingly common management practice throughout the Intermountain West. Thus, Yellowstone Lake provides a case study for evaluating a strategy to remove the apex predator from a large lake.