Hammerhead Sharks

Schooling hammerheads are one of the rarest big-animal sightings in scuba. They prefer deep cool water (20–40m at seamounts, though the species ranges far deeper), school during the day, and disperse at night. Their wide-set eyes give them strong binocular depth perception and, combined with head-swinging, an exceptionally wide field of view, and they detect tiny electrical signals from prey via the ampullae of Lorenzini.

The destination to aim for is Egypt's Red Sea: Daedalus Reef, Brothers Islands and Elphinstone, accessible only by liveaboard. Sightings peak May–Jul when warm-cold thermoclines meet. Sudan's offshore reefs deliver too if you can get there.

Hammerheads are extremely bubble-sensitive. Skilled divers go on rebreather (silent) for closer encounters, but recreational divers can still see them schooling at depth. The trick is staying still, breathing slowly, and arriving early.