Résumé
Conservation of top predators has been emphasised as essential in an
ecosystem due to their role in trophic chain regulation. Optimization of
conservation strategies for these endangered marine top predators requires
direct estimates of breeding patterns and connectivity, which are
essential to understand their population dynamics. While there have been
some attempts to investigate breeding patterns of reef sharks from litter
reconstruction using molecular analyses, direct fine-scale migrations of
female sharks for parturition as well as connectivity at a medium scale,
such as between islands, remain mostly unknown. We used microsatellite DNA
markers and a likelihood-based parentage analysis to determine breeding
patterns of female blacktip reef sharks in Moorea (Society Islands, French
Polynesia). Such an approach demonstrates that while most females gave
birth at their home island, some migrated to specific nursery areas
outside their home range, sometimes going to another island (up to 50 km
across deep ocean). Analysis also revealed that females migrated to the
same nursery on every birthing event. Many offspring showed a high level
of inbreeding indicating an overall reduced population size, restricted
movements and dispersal, or specific mating behaviour. Females represent
the vectors that transport the genes at nursery grounds, and their
fidelity should thus define reproductive units. As females seem to be
philopatric, males could be the ones dispersing genes between
metapopulations. These results highlight the need for conservation of
coastal zones where female reef sharks seems to exhibit philopatry during
the breeding season.