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Sharks, rays, skates and ratfishes all have cartilaginous skeletons. They also have gill slit instead of the gill covers found on other fishes. Their skin contains dermal denticles (like tiny teeth) embedded within their skin, giving it a sandpaper like surface. In fact, their teeth are only dermal denticles enlarged and modified. Most are active fishes and heavier than water. They will sink if they stop swimming. Some oceanic species must swim continuously to move water over the gills in order to breathe. Their senses are acute. They can find a source of a smell, like blood, from as far as ¼ of a mile and can hear low frequency vibrations of a wounded or thrashing animal from a mile away. They can even sense weak electrical fields given off by all living organisms. They can be very dangerous, but are unpredictably so. Except for the Whitetip Reef Shark, most sharks in Hawaii will avoid people. The Bull Shark, Oceanic Whitetip Shark, Blue Shark, and Mako Shark are not found along Hawaii's reefs. These are the species known to attack humans. The Great White Shark is a very rare visitor that prefers more temperate waters. However, the Tiger Shark is not uncommon in Hawaii. It is believed to stay in deep waters during the day and, although dangerous, does not usually threaten humans. This animal is believed to have been responsible for several fatalities, typically spear fishermen and surfers. Oceanic Whitetip Shark This animal has large, rounded dorsal fins with speckled white tips and paddle-like pectoral fins. It is a stocky shark and has a whitish ventral surface. It has a short, blunt snout with sharp serrated teeth. The teeth in the upper jaw are broad, triangle-shaped and completely serrated. Those in the lower jaw are more pointed and serrated only near the tip. It is seldom found near the reefs. It is usually found in the open ocean in the upper 200m where it will be slowly cruising along the surface. It cannot stop swimming. It may reach 11-13 feet, but usually only about 10 feet. They are very inquisitive, persistent and bold and will check out any possible food source, even divers. We came upon one during a surface break one day in open water. We snorkeled with it for about twenty minutes. Needless to say we stayed pretty bunched up. It kept circling our group of about 6 until one of us would separate from the group. At these times it would become bolder, circling in a little closer. We would quickly bunch up again. Scalloped Hammerhead Shark The strangely shaped head of the Scalloped Hammerhead Shark probably allow a certain amount of lift as it swims. The eyes are greatly separated which increases depth perception. Small pits on the underside of the head are sensitive to electrical fields and help to locate prey under the sand. At least 3 attacks on swimmers have occurred in Hawaii, but none of them were fatal. They grow to about 12 feet. Whitetip Reef Shark This is probably the most common of Indo-Pacific sharks and the only shark that is regularly seen on Hawaii's reefs. It has a grayish brown body with white tips on the 1st dorsal fin and upper tail fins. They grow to about 6 feet. They hunt over the reef at night, plucking small fishes and crustaceans from their hiding places. By day, they rest on the bottom in caves or under ledges. We found that they will be found fairly regularly is certain areas over a period of time. At least until they would get tired of having their rest interrupted by a group of gawking divers. They appear docile and lethargic and will allow you to get fairly close, but these animals are not harmless. |
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