Native and non‐native species response to the colonization and subsequent suppression of northern pike <i>Esox lucius</i>

The expansion of northern Pike Esox lucius outside its native range into the western states of North America is a growing problem due to their negative effects on fish communities. Illegally introduced E. lucius were first detected in Box Canyon Reservoir in northeast Washington in 2004. By 2010, the E. lucius population was estimated at more than 10,000 individuals. Between 2012 and 2019, a gillnet suppression programme was conducted, which reduced the E. lucius catch per unit effort in Box Canyon Reservoir by 97% and their biomass by 98%. Between 2004 and 2019, four standardized surveys were conducted to characterize changes in the Box Canyon Reservoir fish community. Even after E. lucius were effectively suppressed, native species showed no signs of recovery during the study. The relative abundance of all native species decreased 82% in total number and 56% in total biomass between 2004 and 2019. Conversely, the relative abundance of non-native species increased 26% in total number and 33% in total biomass over the same period. As an apex predator, E. lucius had a significant impact on the fish community in Box Canyon Reservoir over a relatively short period of time (7 years), and appeared to act as a catalyst to increase the rate of replacement of native species with non-native species, which likely increased the pace of taxonomic homogenization in the reservoir.