Citizen science is often used to assess the distribution and abundance of species, but it can be extended to identify the occurrence of different animal behaviours, generating hypotheses for the fields of behavioural ecology, conservation, and evolutionary biology. Here we use a targeted citizen science approach to map the prevalence and spatial spread of a fish’s unusual hunting strategy across the Caribbean Sea. Using a standardised questionnaire targeting regular scuba divers, we quantified the occurrence of a behaviour termed ‘shadowing’, where West Atlantic trumpetfish (Aulostomatus maculeatus) swim behind or next to another ‘host’ species when hunting prey. While the vast majority of participants observed trumpetfish on nearly every dive, using spatial analyses, we found the frequency of shadowing behaviour was geographically clustered within the Caribbean, particularly to within ~100 km ranges. Our survey also highlighted that shadowing behaviour was more likely to occur in particular habitat types, and with particular host species, suggesting potential mechanisms for such clustering. Our results not only identify a mosaic of different hunting behaviours across thousands of square kilometres, but more generally, demonstrates the power of using citizen science to investigate behaviours over spatial scales that would otherwise be unfeasible.