Is Manual Removal of Nonnative Fish Doing More Harm Than Good? A Study of Lake Trout and Bull Trout in Lake Pend Oreille, Idaho

Invasions of nonnative fish present a major threat to native fish populations. Mitigation strategies are often implemented as a conservation strategy but may fail to reduce negative impacts or deliver intended benefits to native fish populations. The objectives of this study were to evaluate alternative manual netting removal strategies to decrease abundance of nonnative Lake Trout Salvelinus namaycush and increase abundance of native Bull Trout Salvelinus confluentus in Lake Pend Oreille, Idaho. Integrated models were used to estimate population parameters and simulations were used to project abundance of both species under seven levels of netting effort targeting Lake Trout. Although decreasing or ceasing simulated mitigation of Lake Trout reduced by‐catch mortality for Bull Trout, the subsequent increase in Lake Trout abundance reduced survival and decreased abundance of Bull Trout. Failing to account for interactions between native and nonnative populations in manual netting removal programs can lead to ineffective management where changes in native fish populations may be lower or slower than expected if by‐catch mortality is ignored.