Scalloped hammerhead

What it is

This shark belongs to the hammerhead family and is named for its unique head shape. The front edge features a central indentation flanked by two smaller ones, creating a scalloped appearance. Its eyes and nostrils sit at the tips of these lateral extensions. The body is typically grey, bronze, or olive with a white belly for camouflage. It possesses a large, slightly hooked first dorsal fin and a smaller second one. Adults can reach lengths of over four metres, though most are smaller.

Where it lives

These animals inhabit warm temperate and tropical seas across the globe. Their range extends from latitude 46 degrees north to 36 degrees south. They live over continental and island shelves, often staying above 25 metres depth but diving to 500 metres. During the day, they stay near shore, moving offshore at night to hunt. Juveniles prefer shallow bays and mangrove roots for protection and nutrients.

How it lives

They are opportunistic predators with high metabolic needs. Young sharks feed on inshore fish, while adults target larger prey like squid, crabs, rays, and other sharks. Their wide head helps pin stingrays to the seabed. They exhibit complex social behaviour, often forming large schools that may number in the hundreds. This grouping aids in hunting and reproduction. They use Earth’s magnetic field and environmental cues for navigation during long migrations.

Breeding and life cycle

Females give birth to live young after a gestation period of about one year. Litters are large, containing between 12 and 41 pups, likely due to high infant mortality. Mothers return to specific nursery sites, such as mangrove fjords, to deliver their young. Pups remain in these shallow, safe waters for roughly three years before migrating to deeper oceanic feeding grounds. Sexual maturity occurs when sharks reach approximately 2.4 metres in length.

Fish and people

Fisheries target this species for its fins, which command high prices in markets like Hong Kong. It was the first shark listed under the U.S. Endangered Species Act. Overfishing and bycatch in longlines have caused severe population declines, exceeding 95 per cent in some Atlantic areas. Conservation measures include fishing bans in nursery zones and genetic tracking of fin trade. Shark diving tourism offers a non-consumptive economic alternative in some regions.

Status and threats

The International Union for Conservation of Nature lists this shark as Critically Endangered. Primary threats include overfishing for fins and liver oil, along with accidental capture in commercial nets. Slow growth and late maturity hinder population recovery. Marine reserves protect key breeding and nursery areas. Regulations now prohibit retaining these sharks on vessels in several jurisdictions to reduce exploitation and support stock rebuilding efforts globally.

Relatives and look-alikes

It is closely related to the great and smooth hammerheads, though it is generally smaller. It forms a cryptic species complex with Sphyrna gilberti, distinguished mainly by vertebral count. Previously, Sphyrna couardi was considered separate but is now synonymised with this species. Confusion sometimes arises with other hammerhead varieties due to similar head shapes, but the scalloped margin is a key identifier.

Questions people ask about Scalloped hammerhead

Good reading and sources

• Extinction: 'Time is running out' to save sharks and raysBBC, Article

• Scalloped hammerhead on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data