water Article Two Ocean Pass: An Alternative Hypothesis for the Invasion of Yellowstone Lake by Lake Trout, and Implications for Future Invasions Todd M. Koel 1,* , Colleen R. Detjens 1 and Alexander V. Zale 2 1 U.S. National Park Service, Yellowstone Center for Resources, Native Fish Conservation Program, P.O. Box 168, Yellowstone National Park, WY 82190, USA;
[email protected] 2 U.S. Geological Survey, Montana Cooperative Fishery Research Unit, Department of Ecology, Montana State University, MSU–P.O. Box 173460, Bozeman, MT 59717-3460, USA;
[email protected] * Correspondence:
[email protected]; Tel.: +1-307-344-2281 Received: 17 April 2020; Accepted: 4 June 2020; Published: 6 June 2020 Abstract: Preventing the interbasin transfer of aquatic invasive species is a high priority for natural resource managers. Such transfers can be made by humans or can occur by dispersal through connected waterways. A natural surface water connection between the Atlantic and Pacific drainages in North America exists at Two Ocean Pass south of Yellowstone National Park. Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri used this route to cross the Continental Divide and colonize the Yellowstone River from ancestral sources in the Snake River following glacial recession 14,000 bp. Nonnative lake trout Salvelinus namaycush were stocked into lakes in the Snake River headwaters in 1890 and quickly dispersed downstream. Lake trout were discovered in Yellowstone Lake in 1994 and were assumed to have been illegally introduced. Recently, lake trout have demonstrated their ability to move widely through river systems and invade headwater lakes in Glacier National Park. Our objective was to determine if lake trout and other nonnative fish were present in the connected waters near Two Ocean Pass and could thereby colonize the Yellowstone River basin in the past or future.