Long-term Population Monitoring

Monitoring of Yellowstone cutthroat trout occurs on tributaries to Yellowstone Lake during the spring spawning migration, within the lake during the fall, and on streams throughout the park each year. Populations are monitored for abundance, size structure, genetic integrity, and overall health. Recent data show a serious decline in cutthroat trout numbers throughout the lake.

On Clear Creek, a large tributary along Yellowstone Lake’s eastern shore, cutthroat trout were monitored annually using a weir across the stream to guide fish into a trap box and through an electronic counter. Data was obtained almost every year from 1945 through 2007 on upstream and downstream migrating spawners, the duration of the spawning run each season, the timing of spawning peak, and data on the environmental conditions such as stream temperature and discharge. oever, high spring flows in 2008 rendered the weir and traps inoperable. Park staff are curently investigating the feasibility of reconstructing this tool for data collection in future years.

Since 1969, a set of five gillnets of varying mesh sizes has been placed at 11 designated sites for one night each September to assess the Yellowstone cutthroat trout population lakewide. Data are collected on the number and species of fish caught by these nets. (They also entangle longnose suckers and lake trout, two non-native species that were planted in the lake). Scales are taken from the cutthroat trout, which are also weighed, measured for length, and identified as to age and sex. Live cutthroat trout are examined immediately and returned to the lake. Those that died in the net overnight are tested for whirling disease, which is known to be present in Yellowstone Lake.

Elsewhere in streams and smaller lakes throughout the park, Yellowstone cutthroat trout are monitored routinely as a part of resource surveys. Many of these surveys are conducted near ongoing road reconstruction projects. Cutthroat trout populations in heavily fished waters are also monitored by biologists and by a team of directed anglers as part of the Yellowstone Volunteer Flyfishing Program. All sportfish species are monitored parkwide through angler report cards that each person who purchases a fishing permit for the park is asked to return. Data from these report cards is compiled annually to provide park managers with important information on catch rates, fish size, angler use, and angler satisfaction.

Updated 7/28/10