Author: Iain Page, September 2006
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 completely nuts over them.
Just one reported sighting at our local dive sites here in Phuket and Phi Phi brings "whale shark fever" to all of the 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! Of course, they could be blissfully unaware that the elusive whaleshark could be swimming directly above their head as these creatures are generally spotted cruising gracefully just below the surface!
So what do we actually know about these magnificent creatures?
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.
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.
So how does a whale shark get so big? Not by eating humans, that's for sure. Our combination of skin and bones is deinitely not high on the list of any shark's favourite meal.
Whale sharks are actually pescetarians who 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.
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 prior to hatching but inside the mother's body. Therefore, the embryo's food source is the egg yolk and not directly from the mother.
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.
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 tend to turn up randomly all year around the most likely time to see one depends on the area you are diving. During the months of February to April when plankton blooms tend to occur, the best place to see them is north of the Similans Islands at the dive sites of Koh Bon, Koh Tachai and Richlieu Rock. The best opportunities to see whalesharks in Phuket and Phi Phi are during the period of May to October. This may be due to the monsoon wind causing plankton to be transported from the Indian Ocean by surface currents.
However, bear in mind that these are all wild animals. As with all of nature, nothing can be guaranteed or accurately predicted. 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!
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:
If all divers follow these simple rules, we can increase the likelihood of underwater encounters with these beautiful giants. We can also then ensure that those encounters are stress-free experiences for both the whale sharks and the fortunate divers.
1Florida museum of Natural History
2Wilkipedia - online encyclopedia
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