Gray Reef Shark / Halu'u
Document Actions
Gray Reef Shark / Halu'u
Carcharhinus amblyrhynchos
Sharks or halu'u (a general term used by Chamorus for all sharks), differ from other fishes in many ways. Their skin is covered with tiny dermal denticles that are structurally similar to teeth. This gives the skin a rough, sandpaper-like texture. The teeth are actually modified dermal denticles that are continuously formed in rows on the inner surface of the jaws. When an outer tooth is lost, the next available inner tooth takes its place. The fins of sharks have the same skin and texture as the rest of the body and are still at their bases so they can't be folded as in most other fishes. A complex system of pores around the head and sides, coupled with a pair of inner ears enable sharks to detect the vibrations and sounds produced by fishes and other animals at great distances. At closer range, an acute sense of smell enables halu'u to detect minute concentrations of blood or other body fluids from potential prey. Sight is limited by the clarity of the water. At close range, halu'u have an amazing ability to detect the minute electrical fields given off by all living creatures. This enables them to locate prey in complete darkness or hidden beneath the sand. Some halu'u may also use anomolies in the magnetic field of the earth to navigate in what we perceive to be featureless open sea.
There are over 12 species of halu'u in Guam's waters. Most are harmless unless stimulated or provoked. The reef whitetip shark (Triaenodon obesus), reef blacktip shark (Carcharhinus melanopterus) and gray reef shark are the most common sharks on shallow reefs. They are small, reaching a length of about six feet (1.8 m). The gray reef shark can be quite aggressive and territorial and has been known to cause severe but non-fatal bites. The other two generally flee when approached. The tiger shark (Galeocerdo cuvieri) is our most dangerous species. It grows to a length of about 18 feet (5.5 m), will eat almost anything, and has been known to attack and eat divers. Fortunately, it spends most of the daylight hours in water over 200 feet (60 m) deep where encounters with humans are unlikely. However, it occasionally enters shallow water at night or anytime when attracted by dead animals or garbage, or when breeding. Halu'u are at the top of the coral reef food chain. They play an important role in the balance of nature and should not be indiscriminately killed. Halu'u are extremely vulnerable to overfishing. Although they are generally not kept for food, they are often killed when caught so their population is lower here than in more remote areas.
Guam Comprehensive Wildlife Conservation Strategy, 9/27/2005
