The hammerhead is one of the most recognisable animals in the ocean. Its silhouette — that flattened, laterally extended head — signals shark in a way that triggers immediate alarm in most people. That alarm is almost entirely unfounded. Hammerheads are, by the numbers, among the most peaceable large predators a diver can encounter. The data from the International Shark Attack File are unambiguous: 17 unprovoked attacks, zero fatalities, across more than a century of global records.

The International Shark Attack File (ISAF), maintained by the Florida Museum of Natural History, is the most comprehensive database of shark-human interactions in existence. Its hammerhead numbers are striking in what they reveal about actual risk.

Of the 17 recorded unprovoked attacks attributed to hammerhead sharks, only three species have ever been implicated: the great hammerhead (Sphyrna mokarran), the scalloped hammerhead (Sphyrna lewini), and the smooth hammerhead (Sphyrna zygaena). The remaining six species — the winghead, whitefin, bonnethead, smalleye, scalloped bonnethead, and Carolina hammerhead — have no recorded attacks on humans whatsoever. A meaningful portion of the 17 incidents involve provoked encounters: a shark hooked on a line, a spearfisher carrying fish, or a diver who cornered an animal. Defensive behaviour in those circumstances is not predatory behaviour.

The hammerhead’s distinctive head shape — the cephalofoil — is an adaptation for detecting and pinning stingrays on the seafloor, not for attacking large surface animals. Everything about their biology pushes them away from human conflict.

Hammerheads evolved to hunt stingrays, bony fish, smaller sharks, and cephalopods. The cephalofoil is densely packed with ampullae of Lorenzini — electroreceptive pores that detect the weak electrical fields of prey buried in sand. Humans generate no signals that hammerheads have evolved to recognise as food. Beyond diet, hammerhead behaviour toward divers is characteristically cautious. In areas with large hammerhead populations — the Galápagos, Cocos Island, the Maldives, the Red Sea — divers routinely encounter schools of hundreds of hammerheads. These are not carefully managed encounters. They are routine features of diving in these regions, and the sharks consistently move away from human proximity rather than toward it.

Of the nine species, only the great hammerhead (Sphyrna mokarran) warrants any genuine caution. At up to 6 metres and 580 kg, it is large enough to cause serious injury.

Even this designation comes with heavy caveats. Great hammerheads are solitary, deep-ranging animals that rarely come into contact with swimmers or divers. When encounters do occur, the typical behaviour is to circle at distance and then withdraw. Experienced shark divers who regularly photograph great hammerheads in the wild consistently report that the challenge is getting the animal to stay in frame long enough to shoot it, not managing aggression. The small number of incidents involving great hammerheads cluster around spearfishing and baited-water situations — contexts that change the calculus for any large predatory fish.

The scalloped hammerhead, great hammerhead, and smooth hammerhead are all listed as Critically Endangered by the IUCN. A species with zero recorded human fatalities in history is being commercially driven toward extinction.

Hammerhead fins are among the most valuable in the shark fin trade. Their large pectoral and dorsal fins command premium prices in Asian markets. Hammerheads are also caught as bycatch in tuna and swordfish longline fisheries at significant scale. Scalloped hammerhead populations have declined by over 95% in parts of their historical range within living memory — a collapse that has occurred within two human generations. The fear of hammerheads is culturally persistent and factually groundless. The decimation of hammerhead populations is neither: it is happening, documented, and largely invisible to public concern.