Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Lake trout have been intentionally or inadvertently introduced into many lakes throughout the west (Martinez et al. 2009), and the establishment of non-native lake trout populations often causes declines in native species abundance. For example, introduced lake trout (Salvelinus namaycush) threaten to extirpate native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) in Yellowstone Lake, Yellowstone National Park. Consequently, it was deemed that suppression of the lake trout was needed to conserve Yellowstone cutthroat trout in Yellowstone Lake. Gillnetting is the primary method used to suppress lake trout in Yellowstone Lake and this method has been used since the program began in 1995. Unfortunately, lake trout are not the only fish species collected in gill nets. Some Yellowstone cutthroat trout are captured in gill nets and die, thus the exploration of alternative methods to suppress lake trout to minimize bycatch of the targeted species is gaining popularity. Currently, the use of electricity as an alternative suppression method has received considerable attention. Studies have shown that application of electrofishing techniques can increase mortality of fish embryos (Dwyer et al. 1993; Dwyer and Erdahl 1995; Bohl et al. 2010). Most studies have been aimed at providing criteria to reduce mortality of embryos, but it has been suggested that electroshock-induced mortality of embryos may be a means for eradicating unwanted fishes (Bohl et al. 2010). However, application of electrofishing techniques to induce mortality of embryos in lake environments poses certain challenges. Some of these challenges were recently overcome in Swan Lake, Montana. An electrofishing grid was developed and implemented in 2013 in Swan Lake, Montana that caused greater than 90% mortality in embryos up to 20 cm in the substrate (Brown and Guy, Montana Cooperative Fishery Research Unit, unpublished data). The electrofishing grid was also developed for the National Park Service, Yellowstone Lake, but never implemented because of the Federal Government shutdown in fall of 2013. Part of this project will be to experimentally evaluate the efficacy of the electrofishing grid in Yellowstone Lake. Suction dredging is also being considered as a viable alternative suppression method because suction dredging has been found to entrain and cause mortality in fish eggs (Harvey and Lisle 1998). For example, 100% mortality occurred in un-eyed eggs of cutthroat trout (Griffith and Andrews 1981). This project will also experimentally evaluate the efficacy of the suction dredge in inducing mortality in lake trout embryos.