Sharks of Phuket, Thailand: Whale Sharks

Author: Iain Page
Written September 2006

Whale Shark Fever

Whenever divers think of sharks the first one that usually comes to mind is the largest of them all, the whale shark. A combination of its size, beautiful pattern and the fact that it is completely harmless are what makes us divers go nuts over them. Just one reported sighting at our local dive sites here in Phuket brings "whale shark fever" to all dive crew. The signs of this "disease" are easy to spot; your guide will probably spend the whole of every dive looking out into the blue! But what do we actually know about these magnificent creatures?

All In The Name

So where did the whale shark get it's name from? Quite simply the whale shark gets its name from it's size - a shark as large as a whale. The whale shark is in fact a member of the carpet shark family (Orectolobiformes) who derive their name from the fact that their body markings are considered to have a carpet-like pattern. Other members of this family include the leopard shark and grey bamboo shark.

Size Matters

The first identification of this species was a "tiny" 4.6 metre specimen harpooned in Table Bay, South Africa in 1828. Although there is some debate as to how big they get it is thought that whale sharks may grow up to 20 metres¹ in length. However, the largest specimen regarded as accurately recorded was 12.65 metres in length and allegedly weighed in at a whopping 21,000 kilogrammes². Yes, that really is meant to say 21,000. This makes the whale shark by far the largest fish in the ocean.

Food Matters Too

So how does a shark get so big? Not by eating humans, that's for sure. Whale sharks feed on a wide variety of planktonic (microscopic) and nektonic (larger free-swimming) prey, such as small crustaceans, schooling fishes, and occasionally on tuna and squids. As a filter feeder the food is literally filtered out of water passing into its mouth. However, unlike most plankton feeders it doesn't need great motion to get the water to pass through its mouth in the first place but is literally able to suck the water in. This also explains its ability to capture free-swimming prey such as squid.

Baby Talk

So where do baby whale sharks come from? Like most sharks quite how whale sharks mate is rather obscure. However, the end result is the birth of live young (viviparous) although initially it was thought that they laid eggs (oviparous). This was because of the discovery of a single egg off the coast of Mexico in 1956. However, in 1996 a pregnant female was caught in Taiwan and, when cut open, it was discovered that 300 embryos were inside. This actually means that whale sharks are in fact ovoviviparous, a birth method where the embryos develop within eggs but inside the mother's body. Therefore, the embryo's food source is the egg yolk and not from the mother.

Predators

Although juvenile whale shark remains have been found in both blue sharks and marlin there is no doubt that the whale shark's biggest predator is thought to be man. Over-fishing for use as food and for shark fins are the main cause with accidents with boats another cause. The whale shark is currently listed on the World Conservation Union's Red List of Threatened Animals as "indeterminate" status. This category applies to species known to be endangered, vulnerable or rare, but currently lacking enough available information to appropriately place it into one of these three categories.

Thailand Whale Shark Encounters

One of the great things of diving from Phuket is the possibility of whale sharks. These great creatures can be seen not only around Phuket and Phi Phi by day trip but also in the Similans islands and the southern dive sites of Hin Daeng and Hin Muang. In fact, these last two dive sites have probably given divers the greatest chance of whale shark encounters in recent times. Although they can be discovered all year round the most likely time to see one is during the months of February to April when plankton blooms tend to occur. However, bear in mind that, as with all wild creatures, nothing can be guaranteed. It is just a question of being in the right place at the right time. Just ask the Open Water student who recently saw one on only his third open water dive!

Good Behaviour

Although undoubtedly the highlight of many peoples' diving experiences it is important that we, as divers, act responsibly in the presence of these fantastic creatures. The following recommendations have been developed by The Shark Trust, the Australian Department of Conservation and Land Management, PADI International and the Project AWARE Foundation for use when diving with whale sharks:-:

• Do not attempt to touch, ride, or chase a Whale Shark.
• Do not restrict normal movement or behaviour of the Shark.
• Maintain a minimum distance of 3 metres from the Whale Shark.
• Do not undertake flash photography.
• Do not use underwater motorised diver propulsions

Credits

Thanks to Mik Jennings for whale shark photos above. Visit his web site for details of his whale shark experience.

References

¹Florida museum of Natural History
²Wilkipedia - online encyclopaedia

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