Effects of depth on reef fish flight initiation distance: implications of deeper reefs conservation

A reduced susceptibility for local and global impacts has been assigned for deeper reefs compared to historically degraded shallow reefs. Yet, few studies have attempted to analyze the influence of depth on reef fish escape behavior across distinct size classes. By using behavioral response as a measure for prey wariness, the present study analyzed flight initiation distance (FID) for three fishery target and one non-target reef fish species on shallow and deeper reefs in South Atlantic Ocean (Multiple use MPA Costa dos Corais, Pernambuco State). We hypothesized that fish on shallow reefs would have higher FID and detect the human approach sooner and flee at a large distance than individuals in deeper reefs, which would have a late detection, allowing a closer approach. During our field experiment, flight initiation distances average was higher at shallow reefs for three analyzed species, yet each species had specific responses according to individual size classes. For two fishery target speciesE. adscensionisandC. fulva,two intermediate size classes presented higher flight distances at shallow than deeper reefs. However,S. axillarea target parrotfish, demonstrated an unexpected trend with higher FID on deeper reefs for smaller size classes. Interestingly, the non-target species, have also shown differences on wariness across the two analyzed size classes, with higher FID on shallow than deeper reefs. Our results suggest that fish on shallow reefs would detect the human approach sooner and flee at a large distance than individuals in deeper reefs; however, fish response to human presence according to depth is size classes and species dependent. We emphasis the important of no-take zones and the establishment of new marine protected areas on both shallow and deeper reefs in Brazilian waters and elsewhere in order to maintain the integrity of reef fish behavior and consequently ecosystems functioning.