An Evaluation of Lake Trout Suppression in Yellowstone Lake, Yellowstone National Park

Scientific Disciplines
Biological Sciences - Aquatic
cutthroat trout
fishes of yellowstone national park
yellowstone cutthroat trout
Yellowstone national park
lake trout
yellowstone lake
Yellowstone National Park Wyoming
yellowstone national
Yellowstone Lake Yellowstone National Park National Park Service gill
trout suppression
lake yellowstone
lake trout abundance
lake trout suppression
lake yellowstone national park
yellowstone lake yellowstone national
Volume 16, No. 4

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.