Evaluating the Post-Stocking Survival and Reproductive Success of YY Male Brook Trout

Brook Trout have established non-native self-sustaining populations throughout western North America, which are difficult to eliminate and often threaten native salmonid populations. A novel approach to eradicating such populations is using Trojan (YY male) Brook Trout (created in the hatchery by feminizing XY males and crossing them with normal XY males). If Trojan Brook Trout survive after stocking, and reproduce successfully with wild females, in theory this could eventually drive the sex ratios of wild Brook Trout populations to 100% males, at which point the wild population would be eliminated. We stocked Trojan Brook Trout in four streams in central Idaho in 2014; in two of these streams, the wild Brook Trout population was reduced via electrofishing prior to stocking to assess whether diminished competition with wild fish might increase survival of Trojan fish. Apparent survival of Trojan Brook Trout averaged 11% (range 7-21%), and may have been improved in one stream by removing wild Brook Trout. Trojan emigration was minimal in all treatment streams. Genetic analyses are being evaluated to determine if any of the fry collected in 2015 were progeny of Trojan Brook Trout, which would confirm that Trojan fish spawned successfully with wild fish.