The 13-year-old surfer was enjoying a few waves with friends in an area that is banned to swimmers when the shark attacked and dragged Elio further out to sea.
Canestri was pulled from the water by a boat, but the young wave rider had already suffered serious injuries to his stomach, legs and arms.
"Thirteen-year-old Elio was one of our best up and coming surfers. Words can't describe how sad and angry I am. So young! Heartbreaking news," wrote Jeremy Flores, the pro surfer from Réunion Island.
Elio Canestri was 50 feet (15 meters) out into the sea when the shark attack took place. In the last four years, there have been 16 shark attacks in Réunion Island, seven of them resulted in deaths.