MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14770

ABSTRACT: Indo-Pacific coral reefs host diverse assemblages of elasmobranchs from small-bodied mesopredators to apex predators that may vary in the amount of time they spend on reefs. Reef sharks and rays as a group are threatened by human activities and are facing widespread population declines, primarily due to fishing. These human factors may affect not only elasmobranch abundance, but also their assemblage composition. Thus, a better understanding of the factors associated with differences in species-specific abundances and assemblage structure across multiple spatial scales in relatively undisturbed systems could enhance the conservation of shark and ray populations on reefs generally. Here, we used baited remote underwater video stations (BRUVS) to examine species richness and assemblage composition of elasmobranchs across forereefs in French Polynesia, the world’s largest shark sanctuary. Boosted regression tree (BRT) models revealed that island group, latitude, and island geomorphology had the greatest effect on elasmobranch species richness. Assemblages at most islands were dominated by blacktip reef (Carcharhinus melanopterus) and grey reef sharks (Carcharhinus amblyrhynchos) and rays were generally rare. There was, however, significant spatial variation in elasmobranch assemblage composition. This variation was not associated with human factors and appears to reflect species interactions and species-specific responses to environmental variation. Further studies on species interactions (facilitation, competition and predation) among elasmobranchs will provide a better functional understanding of drivers of elasmobranch species composition on individual coral reefs.