Dominique Raquel Lujan
Published: 2020
Total Pages: 56
Get eBook
Lake trout (Salvelinus namaycush) were unintentionally introduced to Yellowstone Lake, Yellowstone National Park, Wyoming, and drastically reduced the native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) population. Gillnetting suppresses adult lake trout since 1995; however, Yellowstone National Park is developing methods to suppress embryos, including adding lake trout carcasses and analog pellets to spawning sites. Decomposing carcasses and analog pellets cause lake trout embryo mortality due to low dissolved oxygen concentrations, but the effects of these methods on lower trophic levels are unknown. We estimated the degree to which adding carcasses or analog pellets to spawning sites altered nutrient limitation, nutrient concentrations, algal biomass, and ammonium uptake. We deployed nutrient diffusing substrates at three sites (control, carcass, and analog pellets) before and after carcasses or analog pellets were added to measure algal biomass in six treatments where nothing (control), nitrogen, phosphorus, nitrogen and phosphorus, carcasses or pellets were added to agar. We measured nutrient concentrations, algal biomass (chlorophyll a concentrations) and ammonium uptake at spawning sites where no carcasses were added (control), site where carcasses were added before lake trout spawned (early season sites), and sites where carcasses were added after lake trout spawned (late season sites) in 2018 and 2019 to investigate the degree to which carcasses caused bottom-up effects in periphyton and phytoplankton. Nutrient diffusing substrates indicated that nitrogen and phosphorus co-limited periphyton before treatments; however, nutrients were not limiting after carcasses or analog pellets were added to spawning sites. Analog pellets appeared to suppress algal biomass and carcasses increased algal biomass ≥2.4x after their addition. Adding carcasses to shallow spawning sites did not alter the concentration of ammonium, algal biomass or uptake compared to the control site. Periphyton had higher biomass and phytoplankton uptake was much higher. Adding carcasses to the littoral zone likely alters small areas but overall had a small effect on algal biomass and nutrient cycling. Estimating how lake trout suppression methods may alter basal resources in the littoral zone of Yellowstone Lake will help managers develop the best plan to control these invasive predators at early life stages.