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

Brook Trout (Salvelinus fontinalis) have been widely introduced across the western U.S. where the species competes with and often replaces native salmonids. Non-native Brook Trout are difficult to eradicate; thus, complementary removal strategies are needed to manage invasive populations. One novel methodology is the M_YY integrated pest management approach, which couples partial removal of a wild Brook Trout population with the stocking of M_YY Brook Trout. If M_YY fish survive to reproduce with wild female Brook Trout, their progeny will be 100% male, which will shift the sex ratio and theoretically extirpate the population. However, the effectiveness of the approach depends on the survival and reproduction of M_YY fish relative to the surviving wild conspecifics. From 2018–2020, we annually removed 50% of the wild Brook Trout populations from three streams and replaced with fingerling M_YY Brook Trout (mean TL = 94 mm, range = 61–123 mm). Annual survival for M_YY and wild Brook Trout was similar in Leandro Creek (M_YY 0.63 and wild 0.63) and Rito de los Piños (M_YY 0.37 and wild 0.46), but lower in Placer Creek (M_YY 0.28 and wild 0.75). We evaluated the reproductive success of M_YY Brook Trout by comparing sexually mature M_YY fish during the spawning season to hybrid (M_YY x wild) F₁ progeny produced in 2019 and 2020. By the second spawning season (2020), M_YY fish comprised 59.8%, 50.4%, and 34.5% of the milt producing Brook Trout, which resulted in 55.1%, 33.3%, and 0% hybrid progeny in Leandro Creek, Rito de los Piños, and Placer Creek, respectively. We demonstrated M_YY fish exhibit similar vital rates compared to wild conspecifics; however, differences among streams highlights unforeseen variables that influence M_YY survival and reproduction. The study offers promising results of the M_YY approach to eradicate unwanted Brook Trout populations.