Lake Trout Suppression Results in Positive Cutthroat Trout Response in Yellowstone Lake

Although efforts to suppress nonnative lake trout increased annually following their discovery in Yellowstone Lake in 1994, the population expanded exponentially and caused a decade-long decline in Yellowstone cutthroat trout. The National Park Service gillnetting program removed more than 500,000 lake trout through 2010, but the rate of population growth continued to be positive. During 2010-2011 a compliance process was completed, agency-NGO partnerships were formed, and fund-raising campaigns were launched to support a large-scale surge in lake trout suppression. An adaptive management strategy was also implemented, wherein benchmarks for gillnetting effort were developed and evaluated during annual scientific panel reviews. Over the past four years, gillnetting effort expended (unit is 100 m gillnet set over one night) was increased from 27,000 units in 2011 to 75,000 units in 2014, resulting in 1.1 million lake trout killed. During the same period, lake trout CPUE declined from 7.8 to 3.7. A positive response by cutthroat trout has been detected as the number caught during annual monitoring has nearly tripled over the past three years. Angler success on the lake for cutthroat trout has also improved, however, visual surveys of tributaries have yet to detect a return of spawning cutthroat trout in spring.