Identifying control intensities to overcome aquatic invader resilience across a range of ecosystem sizes

Abstract Populations of invasive species continue to expand globally, causing extensive ecological and economic damages and are thus frequently the focus of control efforts. To effectively control invasive species populations, management agencies need to apply efforts that will overcome the population's resistance and resilience to disturbance. For aquatic invasive species, initial control efforts often use mechanical removals, which are frequently challenged by size‐selectivity of gears used. Consequently, successful control often requires additional or alternative strategies. Identifying the scale at which alternative strategies need to be applied to benefit control efforts is critical to effective allocation of limited resources. Here, we use a simulation modelling approach to characterize the effect of ecosystem size (as an index of resistance) and population productivity (as an index of resilience) on the effectiveness of a non‐size‐selective method, targeted poison bait, for invader control. We examine the population‐level response to a range of control effort intensities across a range of ecosystem sizes and population productivities. Further, we use our approach to address a case study of ongoing common carp ( Cyprinus carpio ) control in a very large, shallow lake (Utah Lake, UT, USA), where mechanical removal has been challenged by compensatory recruitment, gear limitations and dynamic lake conditions. Poison bait quantities required annually to meet population reduction targets increased linearly with increasing ecosystem size and population productivity. Critically, we identify the presence of minimum effort levels below which management has no impact on long‐term invader biomass, and these minimum effort levels increase with ecosystem size and population productivity. In our case study at Utah Lake, successful carp control would require long‐term application of >11 t of poison bait annually and would require a 65–485× increase in historic annual budget, depending on acceptable level of risk and timeline to success. Synthesis and applications . Our analysis highlights the challenges presented by highly productive invasive species occupying large ecosystems, and the critical need to appropriately scale control efforts to produce the desired impact on target populations. Failure to appropriately scale control efforts can result in expensive long‐term control programs which produce no long‐term impact on target populations.