Species invasions often occur at geographic scales that preclude complete eradication, setting up long-term battles for population control. To understand the extent to which exotic species removal by volunteers can contribute to local invasion suppression and alleviate invasion effects, we studied the activities of volunteers culling invasive lionfish during annual "derby" events in the Atlantic. From 2012 to 2014, single-day derbies reduced lionfish densities by 52% over 192 km 2 on average each year. Differences in recolonization and productivity between regions meant that annual events were sufficient to suppress the invasion below levels predicted to cause declines in native species in one region, but not the other. Population reduction was not related to catch per unit effort, confirming the importance of in situ monitoring to gauge control effectiveness. Culling by volunteers may be a useful tool in areas where exotic species are easily identified and safely captured, and culling can be promoted as an ongoing recreational activity. Strategically guiding volunteer effort toward sensitive or underserved habitats could aid practitioners in optimizing their use of limited resources for invasion management.

Indo-Pacific lionfish have invaded large parts of the western Atlantic, Caribbean and Gulf of Mexico, and have already caused measurable declines in native Atlantic reef fauna. Culling efforts are occurring across the region, particularly on coral reefs, to reduce local lionfish abundances. Frequent culling has recently been shown to cause a shift towards more wary and reclusive behaviour by lionfish, which has prompted calls for halting culls. However, the effectiveness of culling per se is not in question. Culling successfully lowers lionfish numbers and has been shown to stabilise or even reverse declines in native prey fish. In fact, partial culling is often as effective as complete local eradication, yet requires significantly less time and effort. Abandoning culling altogether would therefore be seriously misguided and a hindrance to conservation. We offer suggestions for how to design removal programs that minimize behavioural changes and maximize culling success.

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