The man is in critical condition and has been taken to hospital by air ambulance, ABC News reports.
According to reports, a five-meter-long great white shark was seen in the area earlier in the day.
Rottnest Island is a nature reserve and popular tourist destination outside Perth. The island is best known for its beaches and the opportunity to see the marsupial quokka.
Australia began 2026 with a series of shark attacks. In New South Wales alone, four people were attacked in 48 hours during heavy rains in January; one of them died.
