Latin name

Triaenodon obesus

Other names

Triaenodon obesus

Identification

A small shark with a slender body and a broad, flat head. The snout is rounded and flat. The eyes are oval, horizontally elongated, with vertical pupils and a third eyelid. There are skin folds at the corners of the mouth. The mouth has 42-50 rows of teeth in the upper jaw and 42-48 rows of teeth in the lower jaw. Each tooth has a narrow tip with smooth edges surrounded by small teeth on either side. The placoid scales are small, overlapping and covered with seven ridges.

Features of fish fins

The first dorsal fin is strongly displaced towards the caudal fin and is closer to the pelvic fins than to the pectoral fins. The height of the second dorsal fin is 3/4 of the height of the first dorsal fin. The broad, triangular pectoral fins begin approximately below the fifth gill slit. The lower lobe of the caudal fin is 2 times smaller than the upper lobe. There is a large notch at the tip of the upper caudal blade.

Fish colouring

The shark gets its name from the white tips of its fins. The colouring is dark grey or brown, sometimes the back is darkly spotted. The belly is slightly paler than the back.

Distribution

Widespread in the Indo-Pacific from the Red Sea and east coast of Africa to Indonesia and the Arafura Sea. Their range extends north to the Ryukyu and Ogasawara archipelagos and south to Australia and New Caledonia. They are found throughout Micronesia. They inhabit the waters of the eastern Pacific as far as the Galapagos Islands and the coast of Central America, and are found off the coast of Panama and Costa Rica.

Habitat

They live exclusively on coral reefs, sandy shoals, lagoons and rocky outcrops at the edge of deep water. They prefer clear water and rarely swim near the bottom. This species is most common at depths of 8-40 metres. In some cases they will swim in shallow water no deeper than one metre.

Size

The largest recorded length is 2.13 m, but specimens over 1.6 m are rare. The maximum recorded body mass is 18.3 kg, according to other data - 27 kg.

Behavior

They live in lagoons and on the outer slopes of reefs. They spend the day in shelters under eaves or in caves, often in groups. When they move, they make strong undulating body movements and, unlike other sharks, can lie motionless on the bottom, actively pumping water with their gills. They are sedentary, often returning to the same refuge for many years.

Food and feeding habits

Hunt at night, usually extracting prey from the cracks and crevices of the reef, often breaking off pieces of coral. Their slender and flexible bodies allow them to reach into narrow crevices and holes in the reef and extract prey inaccessible to others. Their main prey is bony fish such as eels, squirrel fish, snapper, damselfish, parrotfish, surgeonfish, triggerfish and goatfish, as well as octopus, lobsters and crabs. Whitetip reef sharks are highly responsive to olfactory, acoustic and electrical cues from potential prey, and their visual system is tuned to motion and contrast rather than clarity. They are able to detect electric fields through the Lorenzini ampoules concentrated on their heads. They are particularly sensitive to natural and artificial low frequency sounds in the 25-100 Hz range produced by a struggling victim. Several sharks may attack the same prey, although each shark hunts individually and competes with individual. These sharks can go without food for up to 6 months. They themselves can be hunted by large sharks.

Reproduction

They are viviparous; developing embryos are nourished by a placental connection to the mother formed by the empty yolk sac. Adult females have one functional ovary on the left side and two functional uteri. The reproductive cycle lasts two years. Males reach sexual maturity at 1.05 m, with an average length of 1.6 m. Females reach sexual maturity at 1.05-1.09 m, growing to 1.58 m in length.

Mating begins when up to five males follow the female closely, nibbling on her fins and body, possibly in response to pheromones she emits that indicate her readiness. Each male tries to catch the female by one of her pectoral fins. Sometimes two males will grab the female from both sides at the same time. The sharks then sink to the bottom, whereupon the male (or males) extend the pterygopodium forward, inflate the siphon sac (a subcutaneous abdominal organ used in seawater to transfer sperm to the female's cloaca) and attempt to insert it into the cloaca. In many cases, the female resists by pressing her belly against the ground and arching her tail stalk. The male has a limited time to copulate because he cannot breathe while holding the female's pectoral fin in his mouth. When the female is ready, the pair will lie side by side with their heads on the bottom and their bodies raised.

Pregnancy lasts 10-13 months. The average duration of pregnancy from the first appearance of "mating" bites was 387 days. Subsequent pregnancies occurred between 57-155 days after parturition. There are 1-6 cubs in a litter (usually 2-3). The number of offspring does not correlate with the size of the female; each female produces an average of 12 offspring during her lifetime. Births occur from May to August (autumn and winter) in French Polynesia, in July (summer) on Eniwetok Atoll, and in October (summer) off the coast of Australia.

Females give birth to pups while moving and bending their bodies; each shark takes less than an hour to give birth. The size of the newborns is 52-60 cm, and their tail fin is relatively larger than that of adult sharks. Compared to other sharks, this animal develops slowly, with newborns growing at a rate of 16 cm per year and adults adding 2-4 cm per year. Sexual maturity occurs at a length of about 1.1m at the age of 8-9 years. On the Great Barrier Reef, males live up to 14 years and females up to 19 years. The maximum life span of this shark can exceed 25 years.

Fishing

Fished off Pakistan, India, Sri Lanka and Madagascar, they are harvested using longlines, gillnets and trawls. The meat and liver are consumed, although there is a risk of poisoning known as ciguatera in certain areas.

Relationship with a person

Rarely aggressive unless provoked. Only 7 attacks have been recorded, none of them fatal.