The three most dangerous sharks are the Great White, the Tiger and the Bull. The next most dangerous are the Gray Reef and the Silky, although others say that the list should include the Spinner, the Blacktip, the Whitetip Reef, the Galapagos and the Dusky sharks.
The 5 Sharks Most Dangerous to Divers
- Divers rarely see sharks.
- Not all sharks are dangerous (some, particularly sluggish bottom dwellers, show no interest in us unless harassed).
- Dangerous sharks are not dangerous all the time (the photographers who took the pictures you see here are alive and well).
There is a great divergence of opinion when it comes to choosing the five sharks most dangerous to divers. The top three – the Great White, the Tiger and the Bull – are undisputed. Beyond that, however, there is no agreement. First of all, many victims of attacks have no idea which shark bit them. They either didn’t see the shark, were too caught up in the horror of the moment to think clearly or are simply unable to tell one shark from another. Second, although each shark has distinctive teeth and these are sometimes left in a wound – a great help in identification – this doesn’t always happen.
Besides the acknowledged top three, we have chosen to feature the Gray Reef and the Silky, both of which have bitten humans on occasion. It should be noted that all of the sharks discussed here occur in areas where people dive. There are other sharks that might attack divers if given the opportunity but they are usually so far from land and in such deep water that divers rarely, if ever, enter their habitats.
Of the five sharks, the Great White is a member of the Mackerel Shark family, Lamnidae; the other four are members of the Requiem family, Carcharhinidae. Of these latter four, the Bull, Gray Reef and Silky are of the same genus, Carcharhinus; although of the same family, the Tiger is a separate genus, Galeocerdo.
The Great White (Carcharodon carcharias) inspires great fascination; so much so that statistics are compiled specifically on its attacks by several organizations. Surfers, snorkelers, free divers and swimmers are much more likely to be attacked than divers. This is because these sharks come close to shore’ looking for their favorite food, seals and sealions, normally found near the surface (as are surfers, snorkelers and free divers).
That only roughly 20 percent of the attacks are fatal led to a now discarded theory that sharks don’t like the taste of humans. Based on more recent observations, it is thought the sharks bite their prey and wait for it to die before coming back to feed. Survivors of Great White attacks were able to get out of the attack area, either on their own or with the help of people nearby.
Great Whites are easily identifiable because of their torpedo shaped bodies, large eyes (with no nictitating membrane), pointed snouts and crescent shaped tail with upper and lower lobes of equal lengths. The shark is dark gray on top, creamy white on the underside. It can grow to lengths of nearly 20 feet.
The second shark most dangerous to divers is the Tiger (Galeocerdo cuvier). Known as the “Hyena of the Sea,” this shark will eat anything. It has not inspired the record keeping the Great White has but numerous attacks have been documented. These attacks occur because the Tiger comes into shallow water to feed. (It is usually a nocturnal feeder.) It is not believed Tigers specifically look for humans but that, as opportunistic omnivores they simply eat anything they find. Surfers and body boarders are most often the targets, typically in the water when the waves are big and visibility low. Divers are rarely attacked, probably because visibility is important to them and few are willing to dive in dirty water.
Tiger Sharks are quite easy to identify. They can grow to lengths of 18 feet and have square snouts with large nostrils. The markings on the body that give the shark its name are quite distinctive, though they fade as the shark gets older.
The Bull Shark (Carcharhinus leucas) is the third shark most dangerous to humans and thus divers. Some consider it more dangerous than the Great White because of its habitat. This unusual fish can live in freshwater rivers and lakes (only those connected to an ocean) as well as saltwater. It is the only shark that can survive in both salt and freshwater; how it is able to do this is not known. The Bull has been found in Lake Nicaragua, the Amazon, Zambei, Ganges, Tigris and Euphrates rivers as well as Lake Jamoer in New Guinea, the Lake Izbal-Rion Dulce system in Guatemala and numerous rivers in Africa, Asia, the Philippines and Australia.
The Bull Shark is dangerous because, like the Tiger, it will eat anything (though in Jaws of Death, Xavier Maniguet says it “is less fond of refuse”). It’s also dangerous because it inhabits shallow, turbid coastal waters in all tropical and subtropical seas. It is never far from land except by accident. This, of course, puts it off beaches, where there are people, giving it an opportunity to attack them.
Although implicated in numerous attacks on humans (particularly off South Africa), this shark is almost never seen by divers. The Bull is hard to identify because it has no distinctive markings and resembles several other sharks. According to John Randall in Sharks of Arabia, the Bull Shark has small eyes and is “Heavy-bodied; snout short and broadly rounded….” The shark is “grey, becoming white ventrally, often with a faint pale grey horizontal band extending into the white of the upper abdomen; fins of small individuals tipped or edged with blackish; these markings become paler with growth….” (Sharks of Arabia). The Bull Shark’s falcate first dorsal fin has a pointed tip. The shark is thought to grow to lengths of nine feet and has triangular, serrated teeth.
Sharks of Arabia says the Gray Reef (Carcharhinus amblyryhnchos) “is one of the three most common species of sharks found on Indo-Pacific reefs.” (The other two are the Whitetip Reef and the Blacktip.) Grays prefer clear waters. According to Sharks in Question: The Smithsonian Answer Book, Gray Reef Sharks “fitted with ultrasonic transmitters were tracked and found to occur in three daytime situations: near ocean-reef drop-offs in loose aggregations of as many as 20 individuals; just above level bottom areas, swimming in polarized schools of as many as 33 individuals; and over shallow reefs and lagoon pinnacles as lone individuals.” Not surprisingly Gray Reef Sharks are frequently seen by divers in such places as Palau and the Red Sea. These sharks are also found off Hawaii and Cocos Island. In some areas of the South Pacific they are fed to entice them to come closer to visiting divers.
The Gray Reef is a small shark, growing to lengths of less than six feet and averaging around five. It has a typical shark shape and resembles several other species. As you may have guessed from its name, the shark is gray on top with a white belly. The snout is round. The chief distinguishing characteristic is the tail fin; the trailing edge is black. The second dorsal and the anal fins are black; the pelvic and pectoral fins have black edges.
In Sharks of Arabia Randall writes, “The author has met five different men who have been bitten by this species, one a diving companion…. and has nearly been bitten himself on two occasions.” If the Gray Reef grew larger it would undoubtedly be more dangerous because it would be able to inflict far greater damage.
These sharks, normally uninterested in divers, can become dangerous when spearfishing is done in their presence.
The Silky (Carcharhinus falciformis) is one of the most abundant sharks, a common deep water pelagic found “in all warm seas” (Sharks of Arabia). Divers encounter it at such places as El Bajo seamount in the Sea of Cortez and the Shark Buoy in The Bahamas. A fast swimmer, the Silky is considered aggressive. Jaws of Death says behavior includes “Intimidation swimming in the presence of divers.” In The Book of Sharks, Ellis quotes University of Miami scientist Dr. Arthur Myrberg as saying the Silky must “be considered a potentially dangerous shark, because of its size, lack of shyness and preference for the upper layers of the epipelagic region in both the Atlantic and Pacific.” This shark has been the subject of several scientific studies.
The Silky grows to lengths of just less than 10 feet. It is a long, slender shark whose upper tail lobe is conspicuously longer than the lower. The first dorsal fin is rounded and falcate. Its pectoral fins are “…large, narrow and falcate…” (Sharks of Arabia). The second dorsal, anal and pectoral fins can have dark tips as can the lower lobe of the tail. Especially telling “is the long free end of the second dorsal and anal fins (The Book of Sharks). The Silky is gray on top, with a white underside. According to The Book of Sharks the name is a reference to “the small size of its dermal denticles,” which make its skin relatively smooth.
The vast majority of divers will never have an unplanned encounter with a dangerous shark and of those who do, fewer still will be threatened; almost none will be attacked. You can minimize your already extremely minimal chances of a shark attack by avoiding murky coastal waters and any places sharks are known to frequent, most especially, pinniped rookeries/haulouts.