Citizen science reveals relationships between human hunting pressure and the abundance and behaviour of invasive lionfish (Pterois spp.)

Abstract Predation can shape the distribution and abundance of animals in an environment, with a major source of predation in some systems now coming from humans. However, measuring the influence of human activities on animal behaviour across large geographic ranges can prove challenging. Here we use a citizen science approach to assess relationships between human hunting pressure and invasive lionfish abundance and behaviour across the Western Atlantic and Caribbean. We collected information from SCUBA diving lionfish hunters about their hunting frequency and observations of lionfish abundance and behaviour. Areas which had been more recently invaded had the highest abundances of lionfish, but the number of lionfish hunters reported in recently invaded areas was lowest. While there was no relationship between the number of hunters in an area and the propensity of lionfish to form groups or utilise shelters, lionfish were more likely to be encountered deeper in areas where there were more hunters. In addition, larger maximum group sizes of lionfish were found at locations with more hunters, and this coincided with areas where lionfish were encountered deeper and where larger maximum catch sizes were reported. This study demonstrates how citizen science can be used to approximate differences in the abundance of organisms and collate observations of their behaviour across wide geographic areas. This approach could be particularly valuable in tracking invasion fronts as invasive species spread.