Residency and spatial distribution of bull sharks Carcharhinus leucas in and around Reunion Island marine protected area

Abstract : A sudden increase in the rates of shark attacks on humans at Reunion Island has been blamed by some on the implementation of a marine protected area (MPA) along the island’s west coast, where attacks, primarily by bull sharks Carcharhinus leucas, were concentrated. We used passive acoustic telemetry to investigate the spatial distribution of bull sharks (N = 36) by quantifying their residency and their frequentation of the MPA and compared it to outside of the MPA. Over the study duration of 17 mo, 18 sharks were detected in the acoustic receiver array, most of which were detected more frequently outside the MPA (N = 148; mean ± SD = 41.5 ± 56.4 visits mo-1 and 17.6 ± 30.5 h mo-1) than inside the MPA (N = 218; 21.4 ± 28.1 visits mo-1 and 7.2 ± 15.2 h mo-1). However, we found individual variation in the sharks’ use of the MPA. Thirteen sharks spent more time outside the MPA than inside, while 5 sharks (all females) spent significantly more time inside the MPA. These results suggest that the spatial distribution of bull sharks is not primarily centered in the MPA along the west coast of Reunion Island, although we identified specific locations where bull shark encounter probabilities are relatively high during particular times of the year. Such higher-risk areas could be targeted as part of the risk management strategy for changes in human uses in order to reduce the risks of negative shark-human interactions observed during the past decade.