Sharks are awe-inspiring animals. They are the marine equivalent of the Formula 1 racing car. Fast. Sleek. Seemingly impassive. Streamlined. Apparently effortless. Beautiful. Yet they have a fearsome reputation.

This reputation is thanks, in no small part, to films such as Jaws and to media reports of sharks attacking swimmers, surfers and shipwreck victims¹. There are, undoubtedly, some species of shark that other water users need to be extremely wary about, such as the Great White. However, the majority of shark species are smaller than humans, relatively docile and present little danger to us, just so long as common sense is used in their presence.

This Entry will introduce the reader to one species of shark that you are likely to encounter if you swim or dive on tropical coral reefs. It will then go on to provide some common-sense rules that should be followed when entering the habitat of warm-water sharks. The author seeks to reassure would-be swimmers that these spectacular fish are not dangerous per se; but they do deserve respect when we enter their habitat.

Blacktip Reef Shark

The Blacktip Reef Shark is the common name for Carcharhinus melanopterus, which is found in shallow tropical and subtropical reefs and lagoons around the world. It is one of the shark species that swimmers, snorklers and divers are most likely to see.

Description

As its name suggests, the Blacktip has black ends to all of its fins. It rarely grows longer than 1.6m² and has a pointed snout and oval eyes. It is grey, or grey-brown, in the upper body, with a white underside.

Their teeth are triangular with serrated edges. Because they are only loosely fixed to the jaw, teeth often break off during feeding. However, new sets of teeth are constantly being made on the inside of the jaw, which move forward to replace the older ones when required. This is why most sharks seem to have three or more sets of teeth.

The mouth is on the underside of the head. When the shark is swimming, the mouth is closed, creating a streamlined profile. When feeding, the jaw opens downwards and outwards, to capture its prey.

Distribution

They are found in almost all tropical and subtropical waters over continental shelves and are particularly abundant in the coral reefs and shallow lagoons of the Indian and Pacific Oceans and the Red Sea³. They are also found in areas of mangrove swamp in the Pacific, where they move in and out with the tides. Very occasionally, they are seen in the brackish waters of tropical river mouths. There are a few Blacktips found in the Mediterranean, which they have reached through the Suez Canal.

Feeding

Blacktips eat mostly small reef fish, as well as small crustaceans and octopus. They are also known to eat land-based snakes from among the mangroves. In Northern Australia, 25% of the stomach contents of Blacktips can be snakes.

Reproduction

All sharks of the Carcharhinidae family are viviparous; that is, they bear live young that have developed inside the body of the parent. Female Blacktips carry anything up to seven young in their bodies and after 12 months gestation the pups are born at a size of 30cm to 45cm long⁴. They start independent feeding immediately and attain sexual maturity in three to four years. Blacktips have an average lifespan of 12 years.

Threats to Blacktip Reef Sharks

The main threat to this species is human disturbance and intervention. Blacktips are caught by inshore fisheries for human consumption⁵. Population numbers are unknown and while it is a very common species, anecdotal evidence suggests that there are significant reductions in their numbers in parts of the Pacific, particularly in the waters around Hawaii.

Are Blacktip Reef Sharks Dangerous?

These sharks can be described as a hazard, rather than as a danger.

A Few Sensible and Simple Rules

• If you are new to tropical or subtropical waters, swim in the company of somebody with more experience, who can reassure you if you get nervous or anxious.

• Keep your eyes open. Blacktips prefer clear, shallow water and are therefore easy to spot.

• Stay calm. All sharks are predators and as such, are attracted to flapping and to an elevated heartbeat, assuming that both are emanating from an injured and/or vulnerable prey species. If you remain calm, they will keep an eye on you, but not cruise close. They are extremely unlikely to attack you, because you are the same size, or probably bigger, than they are.

• Do not swim if you have an open wound of any kind. Sharks can scent blood over a kilometre away. Menstruating women should be cautious about swimming, even when using a tampon. They are unlikely to attack a bleeding human, but they might come a bit closer than feels entirely comfortable and you could attract a group, which can be quite intimidating.

• If you are at all nervous, remain close to your boat, or close to the shore, so that you can quietly and quickly get out of the water if you feel spooked.

• When spear-fishing, empty the keep net onto the shore or into a boat regularly. Do not have dead and dying fish hanging around in the water close to you for too long. They will attract sharks, possibly a group. They will attack a keep net full of dead and dying fish if they are hungry and you could lose your entire catch. As well as going home with a shredded net.

How To Tell If A Shark Is About To Attack

When a shark is relaxed, its pectoral fins⁶ are virtually at right angles to its body and its back is more or less flat. They look sleek, yet languid. In attack mode, their backs arch, or hump, and the pectoral fins flatten back along the body. If you see this behaviour, it is best to get out of the water as soon as you can, even though it is extremely unlikely that a shark the size of a Blacktip will be aiming its attack at you. If there are several sharks in a 'frenzy'⁷ and you happen to be in the way, it is all too easy to be accidentally injured, no matter how small the sharks may be. They do have very sharp teeth.

Is It Safe To Go Into The Water?

Most definitely 'Yes'. If you don't go in you will never experience the awe and the wonder of seeing sharks in their natural habitat, free on the reef.

Use some common sense, don't take risks, respect these wonderful animals and they will keep their distance. And you will have the privilege to watch their extraordinary muscular power and grace. Don't miss it.