If Looks Could Kill

Contributed by Scuba Diver Australasia

If looks could kill, the whale shark would be the most deadly creature in the sea. Up to 14 metres in length, weighing as much as 20 tonnes, and sporting hundreds of teeth, it is outclassed in size only by the true whales. But Rhincodon typus, as it is known to marine biologists, feeds low on the food chain. Its teeth are tiny and its diet consists of planktonic crustaceans, fish eggs, coral spawn, jellyfish, small schooling fishes, squids, and the occasional tuna. Other than the rare collision with a boat, it poses no threat to humans, and has become one of the most prized living destinations for underwater tourists around the world.

Perhaps because their appearance belies their gentle behavior, the sight of whale sharks feeding has captivated divers for decades. Instead of passively filtering planktonic animals from the water column, as is the habit of similarly sized whales and its cousin the basking shark (Cetorhinus maximus), whale sharks migrate around the world’s tropical waters, actively seeking out and sucking in their tiny prey. A cavernous mouth located at the front of the head, rather than slung beneath, is large enough to swallow two humans simultaneously. As it swims to the surface, muscles in the mouth create a powerful vacuum effect then close on their target. Modified gill rakers act like a sieve, seawater is expelled through the gills, and food finds its way into the stomach.

Accidents can happen, of course. But when a whale shark swallows something too large to digest – say a large fish or market buoy – it can cough up the unwanted meal by forcing its stomach up its throat in a process called gastric inversion. Other curious evolutionary adaptations include a checkerboard pattern of light spots and stripes on a dark background covering its back. Scientists suspect the coloring developed as protection from the ultraviolet radiation to which the sharks, which spend a large amount of time feeding near the surface, are exposed.

While the whale shark does not prey on humans, the reverse is not the case. Hundreds are taken each year by directed fisheries and as incidental bycatch in tropical and subtropical oceans around the world. The flesh is the most valuable product, with fisheries in India and Philippines driven by demand from Taiwan, where whale shark meat fetches between US$2 and $7 a kilogram - and there is a lot of meat on a 20-tonne shark. Like many other shark species, its fins are also prized by Asian restaurants serving shark-fin soup. A single large whale shark fin can sell for thousands of dollars, though due to its lower quality, most are used as decorative signage for retailers and restaurants dealing in the fins of other species.
Demand is growing, catches are already falling and some populations appear to have been seriously depleted, according to the IUCN - World Conservation Union. Fortunately, whale sharks recently joined a list of species managed by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). The 'Appendix II' listing means the 166 member countries of CITES must certify that any exports of whale shark products will not harm wild populations.

The campaign to add R. typus to the list was not an easy one. A proposal to add whale sharks was defeated in 2000. A second attempt, co-sponsored by the Philippines (where the species is already fully protected) and India, came just two votes short of passing during an initial discussion at the 2002 CITES meeting. The primary opposition came from member nations resistant to the idea of using CITES to regulate the trade in marine fishes in the first place. But later in the same meeting, following a presentation by Project Seahorse, CITES members agreed to list all species of seahorses on Appendix II, and the precedent of including a commercially valuable species of marine fish had been set. Proposals to list both the whale and basking sharks then returned to the table and passed by slim margins.

While seahorses, among the smallest fishes, may have paved the way for the protection of the largest, much of the support for the listings can be attributed to powerful arguments about the economic importance of whale shark ecotourism in developing countries. The task of securing a future for whale sharks is far from complete, but continued support from the diving community will go a long toward ensuring their survival.

James Hrynyshyn,
Biologist & communications
coordinator with Project Seahorse
www.projectseahorse.org

Rogest Research Team: www.rogest.com

Project Seahorse is an international marine conservation organization that conducts scientific research, establishes marine protected areas, advances environmental education and works to restructure global trade. More information is available at www.projectseahorse.org.

This article was originally published in Scubadiver Australasia

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