Trends in Characteristics of Yellowstone Lake Cutthroat Trout, Associated Factors, and Evidence of a Population Shift

Scientific Disciplines
Biological Sciences - Aquatic
cutthroat trout
yellowstone cutthroat trout
Fish and Wildlife Service
Yellowstone national park
lake trout
yellowstone lake
Lynn R Kaeding USDI Fish Wildlife Service Montana Fish Wildlife Management
Clear creek
Gresswell Geological Survey Northern Rocky Mountain Science Center 1648 South
Wildlife Management Assistance Office
Northern Rocky Mountain Science Center
yct population
yct spawning
yct spawning run
Volume 16, No. 4

Trends in characteristics of yellowstone lake cutthroat 
trout, associated factors, and evidence of a population 

Lynn R. Kaeding, USDI Fish and Wildlife Service, Montana Fish and Wildlife Management 
Assistance Office, 4052 Bridger Canyon Road, Bozeman, Montana 59715
Todd M. Koel, Yellowstone National Park, PO Box 168, Yellowstone Park, WY 82190 todd_koel@
Robert E. Gresswell, U.S. Geological Survey, Northern Rocky Mountain Science Center, 1648, 
South 7th Avenue, Bozeman, Montana  59717
Comprehensive time-series data for Yellowstone cutthroat trout (Oncorhynchus clarkii 
bouvieri; YCT) based on samples taken between 1977 and 2007 from the spawning run 
(spring; n = 29 yrs) of a tributary (Clear Creek) of Yellowstone Lake or caught in gill nets 
set (fall; n = 30 years) at established locations in the lake were examined to identify (1) 
associations between population characteristics within and between capture methods, as well 
as temporal trends in those characteristics, (2) evidence of informative shifts in population 
characteristics, and (3) factors that may have importantly affected the dynamics of the 
lacustrine-adfluvial YCT population of the tributary. Temporal increases in mean TL of YCT 
in the spawning run and of prespawners, i.e., YCT whose gonads indicated the fish would 
have spawned the next year, in the gillnet catch and concurrent declines in run size and 
prespawner catch were suggestive of an effect of YCT population density on the somatic 
growth of the fish. Similarly, a concurrent increase in mean TL of gillnetted YCT 100-199 
mm long was indicated by the polynomial regression results, which also suggested statistical 
change points in the temporal trends for each of those variables. Contrasting those trends 
was that for mean TL of gillnetted YCT 200-299 mm long, whose general decline during the 
past two decades was attributed to predation by nonnative lake trout (Salvelinus namaycush). 
Collectively, these trends provided evidence of a YCT population shift. Correlation results 
indicated YCT in the spawning run could not be unequivocally assigned to any particular lake 
region. Multiple regression analyses showed that Clear Creek run size was strongly affected 
by parental run size 5 yrs earlier and a measure of climate 5 yrs earlier.