Shark, Borneo

Carcharhinus borneensis

phylum: Chordata

class: Elasmobranchii

order: Carcharhiniformes

family: Carcharhinidae

status: Endangered, IUCN

range: China, Indonesia, Malaysia, Philippines

Description and biology

The Borneo shark is a very rare species, little known to humans. It is not a large or dangerous shark. An adult measures about 27 inches (70 centimeters). In coloring, it is brown across the upper part of its body and white underneath. The markings on the shark are not very noticeable. The tips of its dorsal (near the back) fins are dusky and it has light edges on its anal fin. Wildlife biologists (people who study living organisms) do not have much information on the reproductive or other behavior of this species, but Borneo sharks are known to form strong male-female pairs. Fertilization is internal—the sharks do not lay eggs for external fertilization as do most fish. When the female gives birth, just a few young are born and they are developed at the time of birth.

DID YOU KNOW?

Sharks have been around in largely the same form for at least 400 million years. Unlike most fish species, they have no bones. Instead, their skeletons are made up of cartilage, a strong but slightly elastic tissue. Sharks also lack a swim bladder, the air-filled balloon-like organ that keeps most fish upright. Without a swim bladder to keep them afloat, sharks will sink if they are not swimming. Most sharks must keep moving constantly because as they move forward with an open mouth, the water passing across their gills serves as their breathing. All sharks have jaws, and many have up to a thousand teeth arranged in rows. When the teeth are lost, new ones grow in to replace them.

Sharks play a crucial role as predators in ocean ecosystems. To save their energy, many sharks eat old, sick, or otherwise damaged fish—often whole schools of them—thus getting rid of the weaker populations and freeing up resources for the strong.

In recent times, the world's shark population has been in serious decline for a number of reasons; overfishing is the first. Shark became a popular food fish in the United States during the 1980s. By 1989, 16 million pounds of shark were caught by the United States in one year. A management plan for shark fishing was put into place that year. In 2002, however, conservation groups (organizations that work to preserve and manage the Earth's natural resources) charged the U.S. National Marine Fisheries Service with continuing to allow overfishing that was seriously depleting the shark population, especially off the coast of Florida.

Another cause of shark decline is a cruel practice called "finning." People catch a live shark, cut off its fin, and then throw the maimed fish back into the water. The shark, unable to swim without its fin, plummets helplessly to the bottom of the ocean and drowns. Shark fins are very popular in Asia. In some countries, shark fins in soup are thought to work as an aphrodisiac (something that arouses sexual desire). In fact, China and Hong Kong together in the year 1990 imported 5 billion pounds (2.2 billion kilograms) of shark fins. The United States has prohibited finning, but illegal finning of sharks is widespread.

In the early 2000s, the International Union for Conservation of Nature and Natural Resources (IUCN) listed 75 shark species as endangered. By one estimate, 100 million sharks were being killed each year for their fins and more for shark meat. Sharks do not reach sexual maturity until late in life (often at the age of 15) and they have long gestation (pregnancy) periods. Reproduction becomes rare because young sharks are caught by fishers and never have a chance to give birth. Thus, the shark populations have been unable to recover.

Habitat and current distribution

The Borneo shark is native to several inshore coastal areas of the Pacific Ocean, the Indonesian Sea, and the South China Sea. It has been found in tropical areas of Borneo (an island in the Malay Archipelago, formerly Malaysia) and China, and some scientists believe it also occurs in Java, Indonesia, and the Philippines. Since these sharks are very difficult to locate and observe, wildlife biologists do not know the exact population of the species, but it has been estimated at less than 2,500 with a continuing decline in its numbers.

History and conservation measures

All that is known of the Borneo shark was learned from only five specimens, four of which were found in Borneo and one in China. These five specimens were all found before 1937. There were surveys of the shark collections in the markets of Malaysia, Thailand, Singapore, China, and Taiwan in the 1990s and there were no records of any Borneo sharks among them. Therefore, the IUCN has noted the possibility that the species may be critically endangered in the early 2000s.