In-Situ Evaluation of Benthic Suffocation Methods for Suppression of Invasive Lake Trout Embryos in Yellowstone Lake

Suppression of invasive Lake Trout Salvelinus namaycush is an important management tool to use in native fish and ecosystem conservation throughout the U.S. Intermountain West. Lake Trout suppression, primarily by gill netting, has been ongoing in Yellowstone Lake, Yellowstone National Park, Wyoming, since 1995. Additional methods that cause mortality of Lake Trout embryos could be used simultaneously with gill netting to enhance suppression. Our objective was to evaluate the in-situ efficacy of two benthic suffocation methods-tarping with gas-impermeable tarps and Lake Trout carcass deposition to increase the mortality of Lake Trout embryos. Tarping did not increase embryo mortality; mean control mortality was 21 +/- 1.9% (mean +/- SE), and mean tarp-treatment mortality was 20 +/- 2.9%. Lake Trout carcass deposition caused 98 +/- 1.2% mean mortality of embryos at the substrate surface and 100 +/- 0.1% mean mortality of embryos 20 cm below the substrate surface. Hypoxic conditions in the carcass treatments were probably the cause of the high embryo mortality; dissolved oxygen concentrations at the substrate surface declined from 7.74 to 0.06 mg/L when carcasses remained on the treatment locations. The deposition of Lake Trout carcasses shows potential to be an additional suppression method that can induce mortality in Lake Trout embryos through benthic suffocation and could be implemented at Lake Trout spawning sites in Yellowstone Lake.