Hammerhead Shark

The scalloped hammerhead is a distinctive shark in the family Sphyrnidae, easily recognized by its flattened, laterally expanded head called a cephalofoil, which gives the family its common name. Found in warm temperate and tropical coastal and offshore waters worldwide, it is notable for forming large daytime schools, sometimes numbering in the hundreds, particularly around seamounts and islands, before dispersing to hunt solitarily at night. The cephalofoil houses widely spaced sensory organs believed to enhance electroreception and depth perception for locating prey. The species is listed as Critically Endangered due to targeted fishing pressure and high bycatch rates, making it one of the more threatened shark species globally.

• Flattened, laterally extended, hammer-shaped head (cephalofoil) with a scalloped (wavy) front margin and central notch
• Eyes positioned at the outer tips of the head, widely spaced
• Slender, torpedo-shaped body
• Olive-gray to brownish-gray dorsal coloring, fading to a lighter, sometimes white, underside
• Tall, curved, sickle-shaped first dorsal fin
• Adults typically 2.5-4.3 m

Distinguished from the great hammerhead by its smaller, scalloped-edged head and shorter, less strongly curved dorsal fin; the great hammerhead has a nearly straight-edged head margin and a much taller first dorsal fin.

Scalloped hammerheads inhabit warm temperate and tropical coastal waters, continental shelves, and offshore seamounts worldwide, generally in water above about 20 degrees C. They range from the surf zone down to several hundred meters, with juveniles often using shallow coastal bays and estuaries as nursery habitat that offers protection from larger predators. Adults frequently aggregate near seamounts, islands, and current-swept reef pinnacles, likely using geomagnetic cues along these features for navigation during long-distance movements between feeding and nursery grounds. This mix of shallow nursery habitat and deeper offshore range makes the species highly dependent on healthy coastal ecosystems throughout its life cycle.

Scalloped hammerheads are unusual among sharks for forming large daytime schools, sometimes numbering in the hundreds near seamounts, with schooling structure influenced by size and possibly social hierarchy; individuals disperse alone at night to hunt actively for fish, squid, and rays using their sensory-rich hammer-shaped head to detect prey buried in sediment. They are viviparous, giving birth to live pups in shallow nursery bays after an extended gestation, with no parental care following birth. As active predators, hammerheads help regulate mid-level fish and ray populations, and their steep population declines from fishing pressure have raised significant conservation concern across their range.