Once again here on Koh Tao we are spotting Whalesharks with increasing frequency at the moment at dive sites such as Sail Rock, Chumphon Pinnacle and South West Pinnacles. With plenty of interest and questions about these gentle giants of the oceans here are a few interesting facts.
Almost as old as the Dinosaurs!
Whale sharks have been around for over 60 million years which means they survived the last days of the dinosaurs! Whale sharks don’t have a lot in common with whales, besides their massive size and their feeding habits. Sure, they both give birth to live young, but being cold blooded, the whale shark remains a fish whereas the whale is a mammal.
Whale sharks are filter feeders, they open their mouths, let water come in and their bodies filter out the food releasing the water and any debris back into the ocean. They sieve plankton through their gills for much of their nourishment. But they also eat shrimp, algae and other marine plant material, sardines, anchovies, mackerels, squid, tuna, fish eggs and albacore.
The distribution of whale sharks indicates the presence of plankton and the overall health of our oceans. Whale sharks do have about 3,000 tiny teeth, less than 6mm long, but they don’t use those teeth to eat. They also tend to eat in a vertical position.
As Big As A Bus!
Whale sharks grow to be as long as 12m (40ft), however the average size is 5.5m to 10m (18 to 32ft). They weigh up to 18.7 tons (20.6) so around the size of a school bus and twice as big as a great white shark they are indeed the biggest fish in the ocean.
The longest Whaleshark measured was found stranded near Mangalore (India) and had a length of 12.1 metres. However, scientists allow a guess that even larger animals exist. The heaviest specimen ever found (in March 1994) weighed 36,000 kg.
Big they may be, but are they fast? No! They can only reach a top speed of 5kmph, swimming by moving their body side to side (the great white only uses his tail to swim). Their speed and their gentle habits makes it really easy to swim alongside them. However, if they stop swimming, they die. They have to be constantly moving in order for them to breathe.
They are known to populate all tropical oceans and seas, enjoying the warm waters (21 to 25 degrees Celsius) of the South Atlantic, South Pacific and Indian Ocean. Some of them are easily witnessed during their spring migration to the continental shelf of the central west coast of Australia, attracted by the plankton supplied by the Ningaloo Reef.
Up to 400 whale sharks may gather to feed of seasonal food sources. However, they usually roam the oceans on their own and are mostly only seen in the company of remoras. The latter uses the whale sharks as a means of transportation and one of their main functions is to remove parasites. It is very likely that these bony fish also swim into the mouth or spiracle of the whale.
Their reproduction is still a bit unknown. Female whale sharks produce eggs and unlike most fish species the eggs actually hatch inside the mother instead of in the water. Females are thought to give birth to open 300 fully developed live young, many never make it to maturity. They’re only about 0.6m (2ft) long when born.
At the age of 25, the young whale sharks are ready to reproduce, usually when they reach an average size of 4metres. Whalsharks can live up to 100 -150 years.
Adult whale sharks have no predator, except man. They are currently listed as a vulnerable species and we still ignore how many are still swimming freely in the wild. They continue to be hunted in parts of Asia, such as the Philippines and Taiwan despite long-standing bans. They are being hunted for their fins, and meat which is claimed to have medicinal properties.
Their slow-swimming movements makes them easy to be slaughtered in large numbers. According to the IUCN, the Indo-Pacific population of whale sharks is thought to have reduced 63 percent over the past 75 years. The Atlantic population is thought to have reduced 30 percent.
Like human beings with fingerprints, Whale sharks have a unique pattern of stripes and spots on their skin. Organizations like WWF are building a library of these fingerprints to keep track of some whale sharks, whereas others are also tagged and followed by satellite. This allows us to learn more about Whale sharks, their migratory pathways and the global population.
Author: Marie Killinger (PADI DM #389090)