Theses and Dissertations at Montana State University (MSU)
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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 Evaluation of suppression methods targeting non-native lake trout embryos in Yellowstone Lake, Yellowstone National Park, Wyoming, USA(Montana State University - Bozeman, College of Letters & Science, 2017) Thomas, Nathan Andrew; Chairperson, Graduate Committee: Christopher S. GuyNon-native Lake Trout Salvelinus namaycush threaten to extirpate native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in Yellowstone Lake, Yellowstone National Park. Suppression of Lake Trout in Yellowstone Lake has been ongoing since 1995, primarily by gillnetting. Unfortunately, bycatch of Yellowstone Cutthroat Trout is associated with this removal method, which targets adult and subadult Lake Trout. Alternative methods effective at causing mortality in Lake Trout early life stage(s) could be used simultaneously with gillnetting to improve suppression effectiveness. The vulnerability of salmonid embryos suggest increasing Lake Trout embryo mortality is feasible and because population growth rates are sensitive to age-0 survival an effective embryo suppression method could have population-level effects. Thus, the primary objective of this study was to evaluate the efficacy of methods to increase mortality of Lake Trout embryos. In situ experiments tested the effect of suction dredging, electroshocking, tarping, and Lake Trout carcass deposition on embryo mortality. The secondary objective of this study was to evaluate interstitial water flow using NaCl dry injection to better understand the feasibility of using chemicals for embryo suppression. Concurrent laboratory studies have shown that Lake Trout embryos experience high mortality after chemical exposure. Tarping and suction dredging were not effective at increasing embryo mortality. Electroshocking caused 0.92 mortality of embryos at the substrate surface but only 0.38 at 20 cm depth in the substrate. Lake Trout carcass deposition caused 0.99 mortality of embryos, both at the surface and at 20 cm in the substrate. The direction and rate of interstitial water flow was not consistent and future work on a larger scale is needed to inform the feasibility of chemical suppression. Hypoxic conditions within the carcass sites may have caused embryo mortality. In addition, carbon dioxide CO 2 and hydrogen sulfide H 2S are byproducts of organic matter decomposition that harm developing salmonid embryos. Embryo suppression methods are unlikely to replace traditional Lake Trout suppression methods. However, the success of Lake Trout carcass deposition shows potential for the development of an effective additional suppression method that could be implemented on a large scale.