Selectivity of invasive species suppression efforts influences control efficacy.
Abstract
Highly fecund invaders and size-selective suppression efforts often limit the effectiveness of invasive species control programs, as compensatory processes can allow suppressed populations to recover. While population models have long explored how demographic characteristics impact management feasibility, there is a growing need to evaluate how the selectivity of suppression efforts might impact the long-term feasibility of control. We use a simulation framework that integrates age-based selectivity to evaluate the effect of increasing the range of ages selected for during harvest-based invasive species control. We applied this approach to common carp in Utah Lake, the location of one of the world's largest freshwater vertebrate species control programs, to assess how selectivity impacts the level of control effort necessary to achieve management targets. Model simulations suggest that increasing the range of ages effectively targeted by removal gears has the potential to significantly reduce the amount of effort required to reach control targets. We found that increasing selectivity on younger, but mature, age classes allowed the control program to maintain the carp population below the 75% biomass reduction target with only 2.5 times the maximum historic effort level, while further increasing juvenile selectivity conferred minimal benefit. Furthermore, we evaluated historic levels of harvest effort against both previously set management targets and theoretical sustainable harvest targets (MSY). The historic level of suppression effort was less than that required to produce MSY regardless of the selectivity scenario explored, suggesting the control program would be harvesting at a sustainable rate even if it increases the range of ages effectively targeted by removal gears. Synthesis and applications. Controlling highly fecund invasive species becomes much more feasible if managers can identify an approach that targets all adult age classes. Explicitly considering sustainable harvest metrics provides a framework for evaluating a harvest control program's ability to overcome density-dependent processes and achieve management objectives.