Evaluating the success of eradicating nonnative Brook Trout using Trojan Y Chromosome fish in southern Rocky Mountain streams

Abstract Objective Brook Trout Salvelinus fontinalis often outcompete and displace native salmonids in western North America. Due to the limitations of traditional removal methods, managers are implementing the Trojan Y Chromosome approach to extirpate nonnative Brook Trout populations. However, there are uncertainties of the comparative performance (i.e., survival, reproductive success) of YY-male (MYY) fish and their wild counterparts. In addition, it is unclear how effective YY-female (FYY) fish compare with MYY fish for extirpation of wild Brook Trout. To address these uncertainties, we modeled the time to extirpation of wild Brook Trout using 5 years of empirical data, assuming introductions of either MYY or FYY fish. Methods Our simulations assumed varying stocking (0% to 100%) and removal (0% to 90%) scenarios. In addition, we evaluated model sensitivity to changes in the reproductive success and survival of MYY fish. Result The simulations suggest that the average time to extirpation would be 14 years using MYY fish and 8 years for FYY fish, assuming 50% annual removal and 50% initial stocking of the wild Brook Trout abundance. Increasing removal and/or stocking levels resulted in reductions in extirpation times using either MYY or FYY fish. Sensitivity analyses indicated that the model was relatively insensitive to changes in the reproductive success and survival of MYY Brook Trout. Conclusion Our results suggest that either MYY or FYY fish can be used to eradicate wild Brook Trout populations, but FYY fish are likely the most efficient means of eradicating nonnative Brook Trout in streams typical of western North America.