Conservation of Fish Species - Whale Sharks

DjCrazyCol · Guest

Western Australia is privileged to be one of the few places in the world known to be visited by the mysterious whale shark (Rhincodon typus) on a regular basis.

Each year, just days after the mass spawning of corals on the Ningaloo Reef (near Exmouth) in March and April, whale sharks appear in the waters along the front of the reef, remaining for up to a month. It is thought that they come to feed on an explosion of marine life that feeds on the coral spawn.

Most of these visiting whale sharks are immature males. It remains an intriguing puzzle why this particular section of the population visits our coast.

Whale sharks will grow to over 12 metres in length, which is about the size of a large bus. These gentle ocean giants are often confused with whales because of their large size and feeding habits. They are, however, sharks, albeit the least fearsome of this group, and their closest relatives are the nurse and wobbegong sharks.

Whale sharks are not aggressive, and like the second largest of all sharks - the slightly smaller basking shark - cruise the oceans feeding on concentrations of zooplankton, small fish and squid. The whale shark's mouth contains 300 rows of tiny teeth, but ironically, they neither chew nor bite their food.

Instead, the sharks use a fine mesh of rakers attached to their gills to strain food from the water. These rakers are functionally similar to the baleen plates possessed by many whales.

Biologists have speculated that whale sharks feed by literally vacuuming food from the water. However, researchers at Ningaloo have observed that the sharks usually feed by actively swimming through a mass of zooplankton or small fish with their mouths wide open. Whale sharks have also been observed to hang vertically in the water and feed by sucking water into their mouths.

Very little is known about the reproduction of whale sharks, most information coming from a single egg found in the Gulf of Mexico. It is thought that the young develop in egg cases that are retained in the mother's body until hatching. Despite their large adult size, whale sharks are very small at birth, probably 40 to 50 centimetres.

Whale sharks occur world-wide in tropical and temperate seas and are thought to be highly migratory. However, there is little information currently available on this aspect of their behaviour.

Researchers have fitted a number of whale sharks at Ningaloo with "smart tags" that record the animal's location and depth over a long period of time. If, and when, these tags are recovered, they will provide a insight into the migratory habits of this species.

The Department of Conservation and Land Management (CALM), which controls the Ningaloo Marine Park, has prepared log books for tourism operators who take divers out to swim with the whale sharks. The data from these logbooks will be used to build up profiles of individual sharks and migratory habits.

Tourism based on whale shark watching has increased dramatically in the last few years and Government agencies have taken steps to protect these magnificent animals. The Department of Fisheries and CALM have combined to declare an indefinite closed season for this species under the Fish Resources Management Act and the Wildlife Conservation Act.

Specific guidelines for human interaction with whale sharks are outlined in a brochure prepared by CALM.