Known for their spectacular schooling behaviour, the smooth hammerhead gathers into these large groups as juveniles, but as adults they occur singly or in small groups. They hunt for bony fish, small sharks and stingrays and are known to be cannibalistic on occasion. When inshore, their diet consists mainly of skates and stingrays. Pinning their prey down with the hammer, the smooth hammerhead bites chunks from the wings of the stingray until it is immobilised. It is not unusual to see hammerheads with the barbs from stingrays implanted into their heads. In deeper waters they may also feed on crustaceans and cephalopods. In northern Europe, the smooth hammerhead eats mainly herring and bass, and in the Mediterranean, it is known to scavenge from longline fisheries. Other large shark species may prey on juvenile smooth hammerheads, but adults have no natural predators (2). The hammer-shaped head is thought to be a mechanism to spread out the ampullae of Lorenzini – sensory organs that detect electric currents, chemicals in the water, and temperature changes (6).
During an 11 – 12 month gestation, the eggs of the smooth hammerhead hatch inside the female’s body. The embryos are nourished by a yolk sac placenta and during the summer months, once the yolk sac has been used, between 20 and 40 young sharks hatch. Measuring just 0.5 m at birth, males and females reach maturity at 2.1 – 2.5 m and 2.7 m respectively (2).
The smooth hammerhead migrates northward during the summer to find cooler water. When overheating, it can be seen swimming slowly at the surface with the dorsal fin out of the water (5).