Compensatory Recruitment, Dynamic Habitat, and Selective Gear Present Challenges to Large-Scale Invasive Species Control

Control of long‐established invasive species to aid threatened native species presents major logistic and economic challenges. Invasive common carp (Cyprinus carpio ) recently accounted for over 90% of the fish biomass in Utah Lake (Utah, USA), driving many undesired changes to ecosystem structure. Carp control efforts have removed \u3e12,000 tons of carp from the system over 10 yr. However, the impact of recent removal efforts on carp population structure and dynamics remains unclear. We develop an integrated age‐structured population model incorporating carp harvest data with independent standardized monitoring data to evaluate population‐level consequences of the removal effort and evaluate future removal scenarios. Specifically, we estimate the age structure, biomass, and population dynamics of carp in Utah Lake and simulate carp population responses to potential future management strategies. The model estimates carp population biomass has decreased to approximately 27.6% of pre‐removal biomass and 23.4% of the greatest estimated biomass. However, carp removal gear is highly selective of older, larger individuals, and current removal efforts have had little impact on young age‐classes. Evidence of recent strong juvenile cohorts of carp suggests a compensatory response to removal efforts that may increase total biomass as these age‐classes mature. Simulations of carp population response to potential alternative harvest approaches demonstrate that the current gear is unlikely to maintain carp biomass below target thresholds even at substantially increased levels of effort due to gear selectivity, compensatory recruitment, and periodic large recruitment events resulting from lake level increases. A hypothetical gear selecting for juvenile carp is predicted to have a meaningful chance of maintaining low carp biomass, particularly if effort is at least tripled over current levels. These simulations illustrate the value of analytically exploring multiple management approaches when conducting adaptive management. Even when historically used methods have been successful at approaching management objectives, their suitability may change as ecosystem state changes. Periodic re‐assessment of ecosystem state and willingness to explore potential alternative approaches is critical to the long‐term success of any management program as socio‐ecological systems and knowledge change