THE world’s largest fish, whale sharks (Rhincodon typus) can reach lengths of 12m and weigh up to 21 tonnes. Although massive, they are docile and harmless to humans; they feed on tiny marine animals, including plankton, squid, crustaceans and schooling small fishes.
Whale sharks populate tropical and warm temperate seas, inhabiting both deep and shallow coastal waters and the lagoons of coral atolls. Electronic and satellite tagging of whale sharks have found that they can dive to depths of 700m and take long-distance migrations that can last years.
Tracked migrations included travels of over 2,000km from north-west Australia towards Asia. Of three sharks tagged in the Seychelles in 2001, one travelled west to Zanzibar, the second north-west to Somalia and the third travelled over 5,000km to Thailand.
Individuals can be distinguished through the pattern of pale spots and stripes on their bodies, which is unique to each fish. Whale sharks are believed to start breeding at around 30 years and give birth to live youngs. They have traditionally been hunted for their meat, liver oil, fins, skin and gills, and are also accidentally captured in fishing nets targeting schooling fish such as tuna.
In Taiwan, the “tofu sharks” were hunted extensively until an annual quota of 80 fish was set in 2002. The figure was reduced yearly and by November 2007, whale shark fishing was banned in Taiwan.
The International Union for Conservation of Nature Red List of Threatened Species has classified whale sharks as “vulnerable” to extinction. They are also protected by the Convention on International Trade in Endangered Species of Wild Flora and Fauna and the United Nations Environment Programme’s Convention on Migratory Species.
To safeguard the species, conservationists are promoting whale shark tourism. In 2003, Belize reported an economic return of US$3.7mil from whale shark ecotourism and the economic value of a single whale shark there was estimated at US$34,906 annually. Whale shark dives on the Ningaloo Reef in Australia brought in US$5.93mil in 2006.
Sources: Whale Shark and Oceanic Research Centre, Pew Environment Group
Whale sharks in trouble