Identifying Movement Patterns and Spawning Areas of Invasive Lake Trout Salvelinus namaycush in Yellowstone Lake

Gresswell, Robert; Suski, Cory; Parsley, Michael; Koel, Todd; Bigelow, Patricia; Ertel, Brian; Danylchuk, Andy; Cooke, Steven

Annual report of the movement patterns and spawning ares of lake trout. Although the lake trout Salvelinus namaycush suppression program in Yellowstone Lake has been successful at removing large numbers of these predaceous invaders, the number of lake trout captured continues to increase. It is apparent that targeted removal of adult lake trout can have positive effects on population suppression, and capture of adult lake trout can be increased by focusing removal efforts on regularly used travel corridors or spawning areas. Furthermore, destroying lake trout embryos on spawning grounds could be applied synergistically with methods that target free-swimming individuals (e.g. gill nets) in order to maximize suppression of lake trout. Efforts to increase direct removal with gill nets and utilize techniques for destroying lake trout embryos and larvae require knowledge regarding lake trout movement patterns and accurate information concerning the location of spawning areas. To this end, we initiated a collaborative effort of federal and academic scientists with additional funding support from a consortium of four NGOs to identify movement patterns and spawning areas of invasive lake trout in Yellowstone Lake. This pilot study included implanting acoustic transmitters in 141 lake trout and deploying 40 acoustic receivers in 2011. Transmitters emit a signal every 30-90 seconds, and receivers can detect signals up to 0.5 km away. Data were downloaded from the receivers three times in September and October. Preliminary analysis has provided evidence concerning movement corridors and distribution patterns. Receivers in West Thumb, the West Thumb channel to the main lake basin, and along the Breeze Point-Plover Point transect detected the greatest number of unique fish; detections were greatest at the entrance to West Thumb. Daily detections recorded at the north gate to West Thumb varied substantially through time, increasing from lows in late August to a peak during 2weeks in September and then decreasing to initial levels again in mid-October. With the assistance from our consortium partners, we plan to continue the project in 2012. Another 150 lake trout will be implanted with transmitters in the coming year, including 50 transmitters that will be capable of recording depth of individual lake trout over time. Detection data collected by the receivers will be downloaded monthly in June and July, and biweekly in August through mid-October. In 2012, there will be increased emphasis on data analysis, including spatial assessments of location data and movement patterns of lake trout. A website will be developed to provide project updates and visual products to National Park Service personnel and consortium partners.