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The Whale Shark
The Whale Shark is the largest fish in the entire Ocean! The "whale" part in its name describes his length which is comparable to whales. They are also "filter feeders" like whales. Basically, they swim through the water and use their immense gills as a filter, capturing plankton and vegetation as it swims.
The Whale Shark is also called the Rhinocdon typus and it is an enormous shark. It's actually the biggest shark and fish in the world! Would you believe an average adult is the length of a school bus?! They typically grow to about 10-12 m (33-40 ft), but may reach 18 m (60 ft) in length. They can weigh up to 15 tons. Of course no one really knows for sure, because there isn't much known about the size of whale sharks at maturity. People are truly fascinated by these gentle giants, yet surprisingly little is known about their life history, compared to other large sharks.
It's hard to imagine a fish that big, but I can tell you first hand that even a young one is humongous! I went scuba diving in Zanzibar, in East Africa, and our dive master pointed through the water ahead of us excitedly. I saw a beautiful school of silvery fish swim by. Then my eyes focused just behind the fishes, and I realized they were covering a much bigger creature! It was grey with pale spots, and stretched longer than our whole group of divers. Back in the boat, he explained we had seen "just" a baby whale shark. Imagine what it would be like to swim beside an adult!
Since they are filter feeders, they naturally have very large mouths. In fact, the mouth of this beast can reach widths of 1 to 1.5 meters (3 to 5 feet).
In comparison, they have very small teeth but make up for that in quantity. An adult can have up to 300 rows of teeth and include about 3,000 teeth in its entire mouth. Imagine the dental bill!
Just how big do they get? The biggest one ever measured had a length of about 13 meters (42 feet) and weighed more than 22 metric tons (more than 48,500 pounds)!! But even still, experts claim that there must be bigger ones out there. This species can live 100 years or longer. That gives them a lot of time to grow!
This shark is a slow and leisurely swimmer with an average speed of just 5 kilometers per hour (3mph). Because of their gentleness and harmlessness, they are often visited by shark divers.
The Whale Shark On National Geographic
Whale sharks are filter-feeders that travel the world's warm oceans. They are usually solo, but in areas where food is concentrated, whale sharks gather in large numbers.
This is a slow and leisurely swimmer with an average speed of just 5 kilometers per hour (3mph). Because of their gentleness, they are visited often by divers.
The skin has pale yellow markings of stripes and dots on a dark gray background. Each individual has a unique pattern that allows identification, just like human fingerprints. This is an incredible tool for research and conservation. For example, the World Wildlife Fund (WWF) has identified 458 different whale sharks in the Philippines using photos of their skin patterns. Young whale sharks appear to have a tough time out there. The mother leaves her young after birth, and less than 1 in 10 are thought to survive to adulthood. However those that make it may have a lifespan of up 100 or 150 years! Again, no one really knows for sure. Some researchers think the whale shark's closest relative is the relatively puny zebra shark.
These sharks love temperate and warm waters. Therefore, it generally tends to stay in waters along the equator.
Whale sharks are nomadic. genetic studies (of whale shark history and evolution) have shown that they swim all around the globe through temperate and tropical waters (other than the Mediterranean), with no real barriers to movement. They usually stay in deep waters (about 800 m / 2,600 ft), but sometimes move closer to coastal areas, especially near coral reefs.
Over the last 15 years, many studies have placed satellite tags on whale sharks to track their movements. Results confirm that most tagged sharks are very mobile but they swim slowly. They stay within 125 miles of shore, and make regular deep dives (up to 240 m / 790 ft), sometimes coming to the surface to feed. One shark traveled 13,000 km over a three-year period!
Each spring they migrate to the continental shelves around Australia, possibly to feed on the plankton (tiny marine animals and plants) that occur there in great numbers. In fact, marine scientists think the location of whale sharks can be used to measure the presence of plankton and the overall health of our oceans.
Whale Sharks are some of the most social of all sharks. But there is still a cloud of mystery surrounding the exact details such as social structure and dominance.
When it comes to humans, this species poses virtually no threat. Many divers sometimes even hitch a ride with one of these gentle giants! The number one injury to humans from this shark is getting hit with the huge tail fin. This shark is truly a docile creature.
The whale shark is a "filter feeder", like some whales. The mouth is at the very front of its head (different from most sharks who have their mouth on the underside of the head). It is also gigantic, nearly five feet wide. This allows the whale shark to swallow a lot of plankton, using its gills as a "suction filter" while it swims. Relative to other sharks, they have very small teeth but make up for that in quantity. An adult can have up to 300 rows with about 3,000 teeth in its entire mouth! However it can't bite or chew.
Information about the diet comes from the examination of stomachs inside sharks caught by fishermen. Aside from plankton, common whale shark foods include small fish, algae, cephalopods (like squid), jellyfish, and shrimp.
The whale shark's breeding method was debated in the past. Some researchers believed they were egg-layers("oviparous") because egg cases were observed in the oviducts of females during autopsies. Others claimed they were live-bearers ("Viviparous"). It remained a mystery until a 1995 finding proved they give birth to live young.
In fact, like many other sharks, the whale shark is Viviparous.html">OvoViviparous": the embryos develop inside egg cases, but they hatch inside the uterus. The female caught in 1995 contained about 300 embryos, the largest litter size reported for any shark species. These baby sharks certainly don't start out as giants. Normally, they range in size from 30 to 50 cm (11 to 20 in) at birth.
Humans and Conservation
This species poses no real threat to humans. Unfortunately the reverse isn't true. Whale shark deaths due to human activity are caused mainly by collisions with boats and by fishing.
The biggest danger is the international demand for shark products: fins, liver oil (used to waterproof wooden boats), skin, and meat. Sadly the meat is often discarded. Whale sharks are also victims of "Bycatch", which is the accidental capture of non-target species in fishing nets.
Whale sharks are harmless and unafraid of swimmers. So when they form large groupings, they attract human interest. Diving expeditions like the one I was on have become very popular over the last twenty years or so. This kind of ecotourism is a double-edge sword: the increase in diving and boating activities can interfere with whale sharks. However, it also brings increased attention to the study of these mysterious creatures, which is a positive outcome.
Conservation groups like the WWF work with tour operators to raise awareness of whale shark movements and promote safer boating practices, to hopefully avoid collisions with sharks. In turn the operators help to collect information during sightings of the animals. Increased interest means there have been a lot of new observations of these sharks in recent years. Scientists have been able to learn much more about them as a result. This information is badly needed because our knowledge of the species' biology and ecology is still poor. In fact, we still don't know how many exist in the world. Discovery of the mating and pupping areas of whale sharks remains a mystery.
Large marine vertebrates like the whale shark need special conservation attention because they travel so widely around the globe. Since they move past the boundaries of many different countries, programs for managing and protecting their populations have to be international.
Written By: Kara Levevre
Castro ALF, Stewart BS, Wilson SG, Hueter RE, Meekan MG, Motta PJ, Bowen BW & Karl SA (2007). Population genetic structure of Earth's largest fish, the whale shark (Rhincodon typus). Molecular Ecology 16: 5183-5192.
Joung S-J, Chen C-T, Clark E, Uchida S & Huang WYP (1996). The whale shark, Rhincodon typus, is a livebearer: 300 embryos found in one 'megamamma' supreme. Environmental Biology of Fishes 46: 219-223.
Stevens JD (2007). Whale shark (Rhincodon typus) biology and ecology: A review of the primary literature. Fisheries Research 84: 4-9.
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