Latin name

Sphyrna tudes

Other name

Golden hammerhead or curry shark.

Identification

The body of the smalleye hammerhead is streamlined and rather slender. The hammerhead is broad and long, its width is 28-32% of the total body length, the frontal edge forms a broad arch with depressions in the centre and on both sides. The hammerhead of juveniles is relatively wider, more convex and with smaller frontal depressions than in adults. The eyes, located at the ends of the hammerhead, are relatively smaller than in other hammerheads and are equipped with a blinking membrane. The nostrils are located next to the eyes on the front of the hammerhead, with a well-developed furrow running from each nostril to the centre of the hammerhead. The mouth is strongly curved, with 15-16 teeth on the upper jaw and 15-17 rows of teeth on each side of the lower jaw. The teeth are narrowly pointed, with smooth or slightly serrated edges, angled in the upper jaw and vertical in the lower jaw. The placoid scales are oval and covered with five horizontal ridges ending in teeth. 

Features of fish fins

The first dorsal fin is tall and crescent-shaped, with its base posterior to the base of the pectoral fins and the free posterior tip above the base of the pelvic fins. The second dorsal fin is smaller than the first, but quite large, with a concave caudal margin. The caudal edges of the pelvic fins are straight. The anal fin is higher and longer than the second dorsal fin. The lower lobe of the caudal fin is well developed, with a notch at the tip of the upper lobe. 

Fish colouring

The most distinctive feature of this species is its colouration: the dorsal and back fins are grey or yellowish-grey, while the "hammer", flanks, belly, pelvic, pectoral and anal fins are bright yellow to orange with a metallic or iridescent sheen. Newborn sharks are grey, the first dorsal fin and the upper lobe of the caudal fin are dark, the belly is whitish. When they reach 45 cm in length, they acquire a yellow underbody colouration, which turns orange when they reach 50 cm in length. Sharks between 55 and 70 cm become golden, but this colour usually disappears with the onset of sexual maturity.

Distribution

Occurs along the east coast of South America from Uruguay to Venezuela, although it is rarely seen west of the Orinoco delta south-east of Trinidad. There are unconfirmed reports of the species off the coasts of Panama, Mexico and western Florida. Records from other parts of the world are probably erroneous and appear to be the result of taxonomic confusion. It is one of the most common sharks in its range. 

Habitat

This species is found in turbid coastal waters at depths of 5-40 m with a muddy bottom. There is a separation by sex and age: newborns and juveniles up to 40 cm remain in shallow waters and gradually move away from the shore. Adult females are most common at depths of 9-18 m, and large juveniles and adult males are more common at depths of 27-36 m. This species tolerates low salinity and can enter waters with salinities of 20-34 ppm.

Size

Despite the name "giant", this shark is one of the smallest members of its family, reaching a length of 1.5 metres, an average size of 1.2-1.3 metres and a weight of 9 kg. 

Behavior

Adult males and juveniles of both sexes form schools of similar size that do not appear to be associated with reproduction or migration. Adult females appear to be solitary.

Food and feeding habits

The small-mouthed hammerhead is the dominant predator in murky shallow waters where keen eyesight is useless. Young sharks up to 67cm long feed mainly on shrimps of the Penaeidae family, especially Xiphopenaeus kroyeri. Larger sharks feed mainly on bony fish, especially sea catfish and their eggs. Shrimp and caviar contain carotenoids, pigments that can give sharks their golden colour. These sharks also eat blue crabs (Portunidae), squid (Haemulidae) and newborn scalloped bonnetheads. They themselves can be preyed upon by large sharks such as Carcharhinus leucas, and smaller individuals are preyed upon by large bony fish. Their colouration is used for camouflage.

Reproduction

Like other members of the genus, these sharks are viviparous; developing embryos are nourished by a placental connection to the mother formed by an empty yolk sac. Adult females have one functional ovary and two functional uteruses. Ovulation occurs during pregnancy, allowing females to produce offspring annually. 

Details of the hammerhead's life cycle vary according to habitat. Off the coast of Trinidad, mating occurs in August and September, with births occurring in late May and June the following year. There are 5 to 12 pups in a litter. Pregnancy lasts 10 months. Pregnant females swim to shallow, food-rich coastal bays. Newborns are about 30 cm long, with males and females reaching maturity at 80 cm and 98 cm, respectively. Off the coast of Maranhão State (Brazil), sharks are considerably larger, with males maturing at 92 cm and females at over 101 cm. The number of offspring produced is directly related to the size of the female. Maranhão sharks give birth to up to 19 sharks.

Fishing

It is one of the most important commercial species off Trinidad, Guyana and Brazil. Because of the shape of their head, smalleye hammerheads are easily caught in gill nets. Small numbers are also caught in spinning nets and bottom trawls. The International Union for Conservation of Nature (IUCN) has listed this species as Critically Endangered due to high fishing pressure and low reproductive rates.

Relationship with a person

Sharks are shy and harmless to humans. They are caught by artisanal fishermen and their meat is used as food.