Impacts of recurrent culling of invasive lionfish on mesophotic reefs in Bermuda

Invasive lionfish ( Pterois miles and P. volitans ) populations are now pervasive across the Caribbean and Western Atlantic. These generalist mesopredators have the potential to negatively impact reef fish populations throughout their invaded range. Targeted removal by culling has been shown as an effective way to manage shallow-water lionfish densities, however, lionfish are found across a broad depth range, with reproductive populations found at mesophotic depth. This study aimed to determine the efficacy of short-term culling of mesophotic lionfish populations and its impact on resident reef fish populations. Surveys of lionfish and reef fish populations were conducted monthly at three mesophotic reef sites in Bermuda from July to December 2017, with subsequent surveys six and 12 months later. During each survey, all lionfish were removed, measured, and sexed. Lionfish density was found to decrease significantly over the recurrent culling period, with the rate of recolonization declining as density declined, resulting in continued reductions with each subsequent culling. The percent of females also declined during recurrent culling, suggesting that culling may further reduce population stability through impacts to reproductive potential. Reef fish community composition changed throughout the study, with shifts in dominant species and trophic groups despite stable species richness and diversity. However, fluctuations in lionfish density as well as reef fish density and biomass reflected patterns of seasonality indicating that impacts of the physical environment may mask the influence of lionfish culling. Overall, these data suggest that culling of invasive lionfish on mesophotic reefs should target high density sites and seasonal aggregations in order to effectively contribute to management strategies.