Oceanic Whitetip Shark

The **Oceanic Whitetip Shark** (*Carcharhinus longimanus*) has a stocky build, a short, bluntly-rounded snout, and incredibly powerful jaws. This predator grips its prey with the pointed teeth of the lower jaw, serrated only at the tip, while the broader, triangular, serrated teeth in the upper jaw are used to saw, cut and tear the flesh. The first dorsal fin is distinctively large and rounded, and the paddle-like pectoral fins are very long and wide. The oceanic whitetip shark is so named because the tips of its pectoral, first dorsal, pelvic, and caudal fins are often white or show white mottling. These markings are usually black on young individuals with a length under 1.3 metres, and a dark, saddle-shaped marking may also be present between the first and second dorsal fin. Depending on geographic location, the body colour may be brown, grey, beige or bronze, sometimes bluish, while the stomach is usually white, occasionally with a yellow tinge.

## Biology

The diet of the oceanic whitetip shark primarily consists of bony fishes such as tuna and mackerel, but also includes stingrays, sea turtles, sea birds, squid, crustaceans and mammalian carrion. The species is usually solitary, but individuals occasionally congregate in groups during ‘feeding frenzies’ in areas where food is plentiful, such as around whale carcasses. When many different species of shark are involved in a ‘feeding frenzy’, the oceanic whitetip shark usually dominates and may be aggressive towards the other species. This shark is often accompanied by remoras (Echeneidae species), dolphinfish (*Coryphaena*species) and pilot fish (*Naucrates doctor*), and reportedly demonstrates an unusual association with the shortfin pilot whale (*Globicephala macrorhynchus*) in Hawaiian waters. Although the exact reason for this shark swimming along with pods of pilot whales is unknown, it is thought that oceanic whitetip sharks are following them to sources of squid, which the pilot whales are extremely efficient at locating.

The oceanic whitetip shark mates during the early summer in the north-western Atlantic and the south-western Indian Ocean, and females give birth to between 1 and 15 live young after a gestation period of 10 to 12 months. As a viviparous redproducer, the oceanic whitetip shark gives birth to live young born that are nourished throughout the gestation period by a placental yolk-sac. Sexual maturity in both the male and female is attained at the age of six or seven.

## Range and Habitat

The oceanic whitetip shark can be found from Maine in the United States, south to Argentina in the Western Atlantic Ocean, including the Caribbean and Gulf of Mexico,and from Portugal to the Gulf of Guinea in the eastern Atlantic. This species may also occur in the Mediterranean Sea. In the Indo-Pacific, this shark inhabits waters from the Red Sea and East Africa to Hawaii, Samoa, Tahiti and the Tuamoto Islands. In the eastern Pacific, the distribution of the oceanic whitetip shark includes areas around southern California in the United States and south to Peru, including around the Galapagos Islands.

This shark is an oceanic, epipelagic species that is found mainly in offshore, tropical and warm-temperate waters. On occasion individuals are seen in shallower waters near land, especially around oceanic islands(3). This species is found at depths of up to 150 metres.

## Diet

*C. longimanus* feeds mainly on pelagic cephalopods and bony fish. However, its diet can be far more varied and less selective—it is known to eat threadfins, stingrays, sea turtles, birds, gastropods, crustaceans, and mammalian carrion. The bony fish it feeds on include lancetfish, oarfish, barracuda, jacks, dolphinfish, marlin, tuna, and mackerel. Its feeding methods include biting into groups of fish and swimming through schools of tuna with an open mouth. When feeding with other species, it becomes aggressive. Peter Benchley, author of *Jaws*, observed this shark swimming among pilot whales and eating their faeces.

## Behavior

The oceanic whitetip is usually solitary and slow-moving, and tends to cruise near the top of the water column, covering vast stretches of empty water scanning for possible food sources. Until the 16th century, sharks were known to mariners as "sea dogs" and the oceanic whitetip, the most common ship-following shark, exhibits dog-like behaviour when its interest is piqued: when attracted to something that appears to be food, its movements become more avid and it approaches cautiously but stubbornly, retreating and maintaining a safe distance if driven off, but ready to rush in if the opportunity presents itself. Oceanic whitetips are not fast swimmers, but they are capable of surprising bursts of speed. Whitetips commonly compete for food with silky sharks, making up for its comparatively leisurely swimming style with aggressive displays.

Groups often form when individuals converge on a food source, whereupon a feeding frenzy may occur. This seems to be triggered not by blood in the water or by bloodlust, but by the species' highly strung and goal-directed nature (conserving energy between infrequent feeding opportunities when it is not slowly plying the open ocean). The oceanic whitetip is a competitive, opportunistic predator that exploits the resource at hand, rather than avoiding trouble in favour of a possibly easier future meal.

Segregation by sex and size does not seem to occur. Whitetips follow schools of tuna or squid, and trail groups of cetaceans such as dolphins and pilot whales, scavenging their prey. Their instinct is to follow baitfish migrations that accompany ocean-going ships. When whaling took place in warm waters, oceanic whitetips were often responsible for much of the damage to floating carcasses.

## Reproduction

Mating season is in early summer in the northwest Atlantic Ocean and southwest Indian Ocean, although females captured in the Pacific have been found with embryos year round, suggesting a longer mating season there. The shark is viviparous—embryos develop *in utero* and are fed by a placental sac. Its gestation period is one year. Litter sizes vary from one to 15 with the young born at a length around 0.6 m (24 in). Sexual maturity is reached around 1.75 m (69 in) for males and 2 m (80 in) for females.