Scalloped hammerhead (Sphyrna lewini)

Physical characteristics

Adults typically have a laterally expanded head with a central notch and several shallow indentations along the front edge that give the "scalloped" appearance. The body is streamlined with a tall, curved first dorsal fin and a generally bronze to brownish coloration that can appear darker along the back. Growth reaches several meters in length, and sexual maturity is reached at different sizes in males and females. The cephalofoil improves sensory perception, maneuverability, and prey detection.

Distribution and habitat

Scalloped hammerheads are found in warm temperate and tropical coastal seas around the world, occurring between temperate latitudes in both hemispheres. They frequent continental shelves, coastal islands, and also visit offshore seamounts and oceanic waters during migrations. Their preferred environments include shallow coastal areas and deeper offshore zones; see regional habitat summaries at coastal waters resources.

Behaviour and life history

These sharks are often social and form schools that can number from a few individuals to large aggregations; schools are sometimes segregated by size or sex. They are active hunters feeding on benthic and pelagic fishes, cephalopods, and crustaceans. Reproduction is viviparous, with females giving birth to live young after a gestation period; litters can include multiple pups. Juveniles often use coastal nurseries where shallower water offers some protection from predators.

Human interactions and conservation

Scalloped hammerheads have been heavily impacted by fishing pressure, both targeted and as bycatch, and by demand for their fins in international markets. These pressures have caused significant declines in many populations, prompting concern from conservation organizations and regulatory bodies. Measures in some areas include catch limits, protected areas, and international trade restrictions; additional information on cultural and regulatory context can be found via etymology and taxonomic sources and conservation listings. Major threats include overfishing, habitat degradation, and incidental capture in commercial fisheries.

Identification and notable facts

• Cephalofoil shape: the scalloped front margin distinguishes S. lewini from other hammerheads with straighter or more rounded head shapes.
• Social behaviour: schooling is common and can include hundreds of individuals at aggregation sites.
• Conservation status: populations have declined in many regions and the species is the focus of international conservation efforts.

Because of its wide distribution and recognizable appearance, the scalloped hammerhead is an important species for marine ecology, fisheries management, and public awareness about shark conservation.