Having been known to attack humans and boats, blue sharks are considered to be a dangerous species. Twelve unprovoked attacks and four boat attacks have been documented by the International Shark Attack File (ISAF). Three documented attacks resulted from air or sea disasters. There are several accounts where Blue sharks attacked shipwrecked sailors floating in the open ocean. The blue shark sometimes circles swimmers or divers for up to fifteen minutes or more. While not overly aggressive, it is not a timid shark, and needs to be approached with caution, especially if it has been circling, since it may attempt to bite.