The smooth hammerhead (Sphyrna zygaena) is a widely distributed temperate–tropical shark in familySphyrnidae. Its hammer‑shaped cephalofoil enhances maneuverability and electro‑olfactory sensing for huntingpelagic fishes, rays and cephalopods.
Ecology & Life History
Migrations & schools: seasonal movements; juveniles/subadults often school.
Diet: small pelagics, squids, rays and crustaceans along shelves and in the upper ocean.
Reproduction: placental viviparous (yolk‑sac placenta); gestation ~8–11 months; litters of ~20–50 pups (regional variation).
Identification
Straight leading edge with no median notch distinguishes the cephalofoil from the scalloped hammerhead (S. lewini). The first dorsal fin is tall and falcate, but less blocky than in the great hammerhead (S. mokarran). Dorsum grey‑brown to olive, belly white; young may show pale/blackish fin margins.
Size & Longevity
Length: commonly 2.5–3.5 m TL; maximum ~4 m.
Weight: typically 100–230 kg; very large individuals to ~300–400 kg.
Life: about 20–30 years.
Range & Habitat
Nearly worldwide in temperate–tropical seas, from nearshore embayments/river mouths to the upper open ocean (often 0–200+ m). Compared with other hammerheads it shows greater cold tolerance and is common in temperate waters.
Threats & Conservation
Fisheries pressure: targeted/bycatch in longlines, gillnets and trawls; high risk from the fin trade.
Intrinsic vulnerability: late maturity and slow population growth despite large litters.
IUCN global status: Vulnerable (VU). Priorities include quotas/min sizes, spatio‑temporal closures, bycatch mitigation & rapid release (circle hooks, weak links), and trade monitoring/traceability.
