An evaluation of lake trout suppression in yellowstone
lake, yellowstone national park
John M. Syslo* and Christopher S. Guy, U.S. Geological Survey, Montana Cooperative Fishery
Research Unit, Lewis Hall Montana State University, Bozeman, Montana 59717 jsyslo@montana.
Patricia E. Bigelow, Philip D. Doepke, and Todd M. Koel, Center for Resources, Fisheries and
Aquatic Sciences Program, P.O. Box 168, Yellowstone National Park, Wyoming 82190 todd_koel@
Introduced lake trout (Salvelinus namaycush) threaten to extirpate native Yellowstone
cutthroat trout (Oncorhynchus clarkii bouvieri) from Yellowstone Lake, Yellowstone National
Park. A National Park Service gill netting program has removed nearly 400,000 lake trout
from Yellowstone Lake since 1995. Lake trout population size has not been estimated;
therefore, it is difficult to determine the proportion that has been removed. Our objectives
were to (1) examine catch as a function of effort to determine if the suppression program
has caused lake trout abundance to decline, (2) determine if certain population metrics
have changed over time as a function of harvest, and (3) develop age-structured models to
determine the level of mortality required to cause population growth rate to decline below
1.0 (replacement). Catch has continued to increase as a function of effort, indicating lake
trout abundance is increasing. Population metrics were not clearly indicative of a response
to harvest, but were comparable to North American lake trout populations where harvest has
occurred. Results from an age-structured matrix model determined the rate of population
growth was 1.1 given the current rate of fishing mortality and that population growth rate
would be 1.3 in the absence of fishing mortality. The current rate of population growth is
positive; however, it is slower than it would be in the absence of lake trout suppression.
Fishing mortality needs to increase by at least 10 percent to reduce population growth rate
below 1.0 in the future.