UVM Researchers Head to Yellowstone Lake
Evaluating New Ways to Suppress Invasive Lake Trout
- By Lee Gregory Simard
Graduate student Lee Simard and Professor Ellen Marsden recently returned from a research trip to Yellowstone National Park, where they are answering some basic questions about the feasibility of suppressing lake trout populations at their early life stages in Yellowstone Lake. Lake trout is an invasive species in Yellowstone Lake, and is outcompeting and threatening the survival of the native Yellowstone cutthroat trout. Cutthroat trout populations have shown a marked decline since the invasion by lake trout, leading to a negative, cascading effect across the Yellowstone ecosystem - many avian and mammalian species rely on the cutthroat trout as a key prey source.
Following their discovery in Yellowstone Lake in 1994, the lake trout population has grown exponentially, leading to a suppression program led by the National Park Service. Over 300,000 adult lake trout were removed with gillnets and trap nets in 2013 alone, but the population remains extremely high. Other control methods have been proposed to target lake trout eggs and newly-hatched fry before they leave spawning reefs; the hypothesis is that by targeting multiple life stages at once, suppression will occur faster. However, very little is known about lake trout reproduction in Yellowstone Lake. Simard’s Master’s research will evaluate if early life history suppression is likely to have an impact on the overall lake trout population in Yellowstone Lake.
Sampling last autumn showed that egg densities around Carrington Island, one of the only known spawning sites in the lake, were relatively low for such a large population of lake trout, indicating that additional spawning sites likely exist throughout the lake. During their most recent sampling in June, which began just five days after the ice went out on Yellowstone Lake, Simard and Marsden searched for additional sites that could targeted for early life stage suppression. Seven locations across the lake were sampled with two underwater remotely operated vehicles (ROVs) built and adapted by colleagues Dylan Olson and Dr. John Janssen from the University of Wisconsin-Milwaukee. Both ROVs were equipped with a live feed video camera, electroshocker, and suction sampler. The shocker was used to draw out and stun any small fish hiding in the substrate, and the suction sampler captured the stunned fish and brought them to the surface. Three new locations were identified as potential spawning sites and lake trout fry were confirmed on a fourth site, providing additional locations where suppression efforts will take place.
Many of the lake trout questions on Yellowstone Lake are pertinent to current research on Lake Champlain. A strong lake trout population exists in Lake Champlain, but numbers are maintained entirely through stocking because their fry, although abundant after emerging from eggs, do not survive their first year of life. By comparing why early life stages are doing so well in Yellowstone Lake but so poorly in Lake Champlain, Simard and Marsden hope to elucidate the mechanisms preventing survival of young lake trout in Lake Champlain.