Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Introduced 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, we 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/m2 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.