Test of a conservation intervention highlights temporal variability in hybridization dynamics in Catostomus fishes

Non-native species are a leading threat to fish biodiversity. They pose risks to native populations through human-mediated introductions resulting in hybridization events, which could result in demographic or genetic swamping. Catostomus fishes in the Upper Colorado River Basin are an example of this. Extensive hybridization occurs between non-native white suckers ( C. commersonii ) and native flannelmouth and bluehead suckers ( C. latipinnis and C. discobolus ). This system provides a suitable model for using genomic analyses to test the efficacy of an intervention to reduce the abundance of non-native species and production of hybrid offspring. This study implemented a Resistance Board Weir (RBW) as a fish barrier across Roubideau Creek, a tributary of the Gunnison River in Colorado (USA), to restrict non-native sucker participation in spawning events. Conducted over four years, the study gathered genomic data from larval fish samples, pre- and post-implementation of the RBW. We used genomic data to determine the efficacy of a RBW at limiting non-native and hybridized sucker larval production. We found no significant effect of the weir on the proportion of white sucker ancestry in larval fish across the four years of the study, which included three years of weir usage when access was successfully controlled for variable amounts of time. Overall, this work provides insight into the efficacy of a resistance board weir as a management tool for non-native suckers, and highlights interannual variability. This work contributes valuable information for policy and fisheries management in Colorado.