Evidence of a limit to benefits from culling lionfish

Biological invasions threaten ecosystems worldwide, with invasive predators such as lionfish (Pterois spp.) altering marine communities through predation, competition, and habitat disruption. Since their introduction to the western Atlantic in the 1980s, lionfish have rapidly expanded their range and contributed to declines in native reef fish populations. In response, management agencies have implemented targeted removal programs, although their effectiveness, particularly across broad spatial and temporal scales, remains uncertain. We evaluated the effects of removals (culls) at two temporal frequencies by quantifying the densities of both lionfish and potential prey over two years at experimental and non-removal control sites in Florida's Biscayne National Park (BNP). Removals conducted at one-month intervals resulted in moderate reductions in lionfish density but removals at four-month removals did not result in appreciable changes in density. Neither treatment produced substantial changes in lionfish biomass or native prey abundance. Importantly, the magnitude of change in lionfish density following removals depended on the initial lionfish density at a site. Together with previous work, these results suggest that removals are less effective at reducing lionfish densities and enhancing prey assemblages once lionfish densities are already low. Our findings underscore the importance of monitoring lionfish density when evaluating the ecological efficacy of removal programs.