SHARKS OF HAWAII
There are about forty species of sharks of the 450 species of fish that occur in (i.e., are endemic to) Hawaiian waters, ranging in size from the deep-water Pygmy Shark (Squaliolus laticaudus - about 8 inches) to the Whale Shark (Rhincodon typus - up to 50 feet or more). About eight species are commonly seen near shore. The most frequently encountered are the Sandbar, Reef Whitetip, Scalloped Hammerhead, and occasionally Tiger.
These inshore species are top-level carnivores, feeding primarily on fishes. Their function in reef ecosystems is not fully understood, but they are believed to improve fish populations by removing sick and injured fish, leaving the healthiest to reproduce. Sharks have extremely well-developed sensory capabilities. They can detect sounds and and smells from prey at great distances (up to two miles or more, depending on water conditions). Their eyesight is good, but depends greatly on water clarity.
As sharks approach their prey, they can detect the faint electrical fields give off by all living organisms. Receptors on their snouts, known as ampullae of Lorenzini, allow sharks to locate their prey without seeing it. Using these senses, sharks can find prey at dusk, night and dawn, which is when inshore species are generally believed to feed. Sharks are very well aware of their environment and appear to be fairly curious by nature. They are aware of people in the water before people are aware of them. Encounters between sharks and people are infrequent, and most inshore species pose little threat to humans.
While any shark may be potentially dangerous, only a few species of Hawaiian sharks are known to attack people. They include the Tiger, Galapagos, Gray Reef and Scalloped Hammerhead. The latter two appear to attack only when provoked. The Tiger and Galapagos are most aggressive. A Tiger shark is easily recognized by its blunt snout and the vertical bars on its sides. A Galapagos shark is harder to identify; however, any large (over six feet) gray shark with no conspicuous markings seen in inshore waters is probably a Galapagos.
Tigers are considered the most dangerous sharks in Hawaiian waters. (Great White Sharks - Carcharodon carcharias, which are also very dangerous, are rarely seen in Hawai`i.) Because of their size and feeding habits, they occupy the very top niche in inshore food chains. Tigers seem to come into inshore waters in Fall, and stay through Spring. They appear to move offshore somewhat in Summer, but this remains to be confirmed. Like other inshore species, Tigers seem to feed mostly during night and twilight hours. Tigers are often attracted to stream mouths after heavy rains, when upland fishes and other animals are swept out to sea. They can easily locate prey in such murky waters. Tigers are also attracted to waters frequented by fishing boats, which often trail fish remains and blood. Of all the inshore species, Tigers have the most widely varied diet. They eat fish, lobsters, birds, turtles, dead animals, even garbage. It's not known how long Tigers can go without eating, but they soon seem to feed whenever a food source is present.