SHARK SPECIES IN HAWAII

    Sharks are among the oldest animals inhabiting the earth, having been around for roughly 400 million years in an almost unchanged form. They fall into the cartilaginous group of fishes, because they have relatively flexible endoskeletons made of cartilage rather than bone. Overall there are a total of about 750 species in this class, including rays, skates, ratfish, and chimaeras. Sharks comprise roughly 370 species out of that total. In Hawaii, there are approximately 40 species of sharks present. Of these, only about eight species are commonly seen, including tiger sharks, blacktip reef sharks, whitetip reef sharks, and grey nurse sharks. The three species discusses below are the whale shark, which is the largest of all sharks species, the tiger shark, which is a common aggressive predator in Hawaii, and the blacktip reef shark which is a relatively docile shark which frequent the littoral fringe of the islands.

Whale Shark; (Rhincodon typus)

  Hawaiian name: Lele waía

DISTINGUISHING CHARACTERISTICS:

Whale sharks have alternating thin white vertical bars and columns of spots on a dark background, with long ridges along the upper side of the body and a prominent lateral keel. The narrow mouth extends across the full width of its flattened head. The eyes are small and far forward on the head. Each nostril has a small barbel and the gill slits are long and extend above the pectoral fins. Above the relatively small pelvic fins are the first of two dorsal fins (Taylor 1993). The powerful caudal fin is semicircular. Like many species of sharks which hunt near the sea's surface, whale sharks are counter-shaded; they have white bellies, which makes them hard to see if there are predators underwater looking up at them, and dark backs, which makes them difficult to see if predators are looking down on them. It has been suggested that the pale spots and lines on their backs are also camouflage. Whale sharks are often called 'gentle giants' due to their complete lack of aggression. Divers often swim with these creatures, even catching rides on their backs.

SIZE:

The whale shark is believed to be the largest fish inhabiting the ocean, perhaps reaching lengths of close to sixty feet. The average length of these animals, however, is between 35 and 45 feet. Females are believed to be smaller than males. There have been reports of juveniles whale sharks scarcely spanning fifty centimeters.

click to enlarge image

DIET:

The whale shark normally feeds on or just below the surface. These sharks feed by filtering small planktonic organisms out of the water through its 5 gill slits which have fine gill rakers. The whale shark's gills have two functions: in addition to extracting oxygen from seawater, the gills filter the tiny planktonic organisms on which the shark feeds. When a whale shark is feeding it pumps large volumes of water over its gills and out its gill slits. The shark's gills have very fine gill rakers which function as sieves and strain plankton from the water. It has on occasion, been observed eating fish larvae, krill, squid and sardines. The gill slits are relatively large, reflecting its method of feeding - the basking shark alone has bigger gills. One of the most noteworthy characteristics of the whale shark is its enormous head and mouth. The mouth spans the entire length of the head, which measure up to five feet.

REPRODUCTION:

In 1953 a shark egg case containing a 14.5-inch [36.8 cm] whale shark embryo was found in a trawl net in the Gulf of Mexico. The find created a controversy that lasted 42 years; some scientists had speculated that whale sharks were oviparous (egg laying), while others believed they were viviparous (livebearers) and the egg resulted form a premature birth. The debate ended in 1995 when a team of scientists from National Taiwan Ocean University examined a 35-ft pregnant whale shark that had been harpooned by a Taiwanese fisherman. Her twin uteruses contained 300 embryos ranging in size from 16 to 25 inches in length - proof that the embryos emerge from egg cases while still inside the mother's body and that whale sharks are viviparous (Faughnan 1980).

HABITAT:

They are pelagic and they are often seen with schools of pelagic fish, especially trevally (Hawaiian: ulua). Although they are not extremely common in Hawaii, they can be seen around the islands on occasion (Pope 1973).      

Tiger Sharks- also known as Leopard Sharks -Galeocerdo cuvier

Hawaiian: Niuhi

DISTINGUISHING CHARACTERISTICS:

            Tiger sharks are perhaps the most easily distinguished of all common shark species in Hawaii. Physical characteristics of a tiger shark include a large, thick-body with a blunt snout, and the presence of a first dorsal fin which is much longer than the second. The caudal fin is long and pointed, and there is a dermal ridge along the back between the two dorsal fins. In young sharks of this species, the vertical stripes that run from the gill area to the upper lobe of the caudal fin are heavily defined. As the shark grows, these marking fade, but can still be made out in some full-grown adults (Taylor 1993). In the Hawaiian islands, and indeed in every habitat that tiger sharks are found, their reputation as aggressive attackers is well-founded. These animals have been known to attack humans on many occasions, and serious precautions should be taken in areas where they are known to frequent. Although tiger sharks are generally sluggish, when they sense prey, they become aggravated very quickly.

SIZE:

   Although tiger sharks have been reported to grow to a length of thirty feet, evidence supporting this is yet to be acquired. The largest documented tiger shark spanned 18 feet. Generally, however, the average size of a full-grown tiger shark is between twelve and fourteen feet.

click to enlarge image

DIET:

             Tiger sharks are renowned for being the garbage disposals of the ocean, eating almost anything and everything. Items as varied as license plates, turtle shells, and fishing gear have been found in the stomachs of these sharks (Faughnan 1980). In general, tiger sharks hunt in both pelagic and littoral zones of the ocean. Due to this, they consume a wide range of prey, including other sharks, large and small fishes, sea turtles, cephalopods, and anything else readily available.

REPRODUCTION:

            Tiger sharks are viviparous creatures, with females bearing litters of up to fifty or more embryos. The gestation period may last as long as two years, after which juveniles measuring about two feet are born. These creatures lead solitary lifestyles aside from the time spent together mating.

HABITAT:

            Tiger sharks are found in waters throughout the Pacific, Australia, and parts of Asia. The ability of these sharks to reside in both pelagic and reef habitats greatly increases their range. It has been observed that tiger sharks often frequent shallower areas at night and deeper areas during the day.   

Reef Blacktip Shark - Carcharhinus melanopterous

Hawaiian name: Manō pāíele

DISTINGUISHING CHARACTERISTICS:

            The blacktip reef shark has a light grey coloration which fades to white around the ventral area. Their bellies are white, which is a camouflage mechanism often employed by fishes. This makes it difficult for them to be seen by predators lurking in the water beneath them. Blacktip reef sharks have short, rounded snouts with prominent nasal flaps (Taylor 1993). The most noticeable feature and the one for which they are named is the dark coloration on the tip of the dorsal and lower caudal fins. These sharks are active swimmers, generally cruising near the sandy bottom often in caves but sometimes visible cruising at the surface in very shallow, wading-depth waters; either singly or in small, loose aggregations. Activity levels increase markedly at night which is when they are thought to do the majority of their hunting (Pope 1973). These sharks are perhaps the most common aquarium sharks as their juvenile forms are precise scale models of larger adults. They thrive in such settings. Due to their size, blacktip reef sharks are not viewed as a threat to humans. When they do attack, the result is usually a small nip on the ankles or legs. In Hawaii there have been no documented fatalities attributed to these sharks.

SIZE:

            Blacktip reef sharks are among the smaller sharks found in the Hawaiian islands. They generally range in size from four to five feet, with a maximum length of six feet. It is partially due to this fact that they are not considered dangerous to humans (Pope 1973).

DIET:

            As benthic reef sharks, the blacktips mainly rely on foods which they can gather from the reef. Such foods includes crustaceans, cephalopods such as octopuses (Hawaiian he'e), reef fishes including travalli (ulua), mullet ('ama'ama), and snapper (ta'ape).

REPRODUCTION:

            The reproduction of blacktip reef sharks is viviparous. Generally, females bear a dozen or less young per litter. The pups are born with a length ranging from twelve to fourteen inches.

HABITAT:

click on the shark to go home