Whale Shark FAQ
by Shark Research Institute
What are the whale sharks feeding habits?
Whale sharks are planktivores, meaning that the feed primarily on plankton, which are microscopic creatures found in huge quantities throughout the oceans. They will also eat sardines, anchovies, mackerel and the occasional small tuna.
When a whale shark is feeding, it pumps large volumes of water over its gills and out its gill slits. The shark’s gills have very fine gill rakers which function as sieves and strain plankton from the water. This is known as “filter feeding.”
Even though the whale shark is a planktivore, it still has a mouthful of teeth—some 3000 teeth in 300 rows, as a matter of fact. That’s why the whale shark is known as Rhincodon, which means “rasp-tooth.” However, these teeth are very small (less than 1/12 of an inch), so they essentially serve no purpose.
How long do whale sharks live?
Scientists don’t know for certain how long whale sharks live. We do know that some species of sharks that live for 100 years are not able to breed until they are 20 years old. This means they must spend 1/5th (20%) of their lives evading capture until they can reproduce at all. It appears that male whale sharks are not able to breed until they are about 30 years old. If 30 years is 1/5th of a whale shark’s expected lifespan, it may then live for well over a century, possibly even 150 years or longer.
What about whale shark reproduction?
In 1953, a shark egg case containing a 14.5 inch [36.8 centimeter] whale shark embryo was found in a trawl net in the Gulf of Mexico. The find created a controversy that lasted 42 years; some scientists speculated that whale sharks are oviparous (egg laying), while others believed they were live-bearers and the egg resulted from a premature birth.
In 1995, the controversy ended when a team of scientists from National Taiwan Ocean University examined a 35-foot [10.6 meter] pregnant whale shark that had been harpooned by a Taiwanese fisherman. Her twin uteruses contained 300 embryos ranging in length from 16 to 25 inches [40 to 63 centimeters]. This was proof that whale shark embryos emerge from egg cases while still inside the mother’s body, and that whale sharks are therefore live-bearers. Of the 300 embryos, 15 were fully-developed and ready to be born.
Newborn whale sharks measuring 21 to 25 inches in length [55 to 63 centimeters] have been caught in the Pacific Ocean off the coast of Central America. In January 1996, there was an unconfirmed report that newborn whale sharks were found in the Marshall Islands. Newborn whale sharks have also been caught in the Gulf of Guinea, the Atlantic Ocean, and the Persian Gulf.
Nobody knows how frequently whale sharks reproduce, and the gestation period for the animal is also unknown. In fact, no one has ever witnessed a mating or birthing event.
: Range and Migration
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