Whale Shark Biology

The Whale Shark is the biggest fish in the sea and only a few species of whale are larger. It is thought to reach up to 20m in length and a massive 34 tonnes in weight, yet it feeds on microscopic plankton rarely more than 3mm in size! The combination of its immense size and characteristic checkerboard pattern makes the Whale Shark almost unmistakable and completely unforgettable.

There is a great deal of mystery surrounding Whale Sharks due to the difficulty and costs involved in studying them. Therefore, much of the information we have is based on a limited amount of evidence resulting in a certain degree of uncertainty.

At birth Whale Sharks are around 55–64cm in length.  The only pregnant female caught to date was nearly 11m, weighed 16ft and contained 307 embryos measuring 42-63cm in length.

Estimations of sexual maturity are as high as 30 years (6m for males and 8m for females) with a life span of anywhere between 60 and 100 years.

Whale Sharks are included in the 25% of sharks that are ovoviviparous. Ovoviviparity is the method of reproduction where fertilised eggs develop within the womb. The unborn young are nourished by the egg yolk rather than the female, who gives birth to fully developed live young. Other sharks are viviparous (the embryo develops inside the body of the female) or oviparous (eggs are laid by the female and develop outside the body).

If it is normal for all female Whale Sharks to carry up to 300 embryos, then whale sharks could be one of the most productive live bearing shark species.  However, this information is based on only one individual. It is unknown how often Whale Sharks reproduce, how many embryos survive or even where Whale Sharks go to mate or give birth. The question is; if Whale Sharks are this fecund why are there so few in the Oceans?

The Whale Sharks that have been tracked are generally slow swimmers, averaging 1km/hr, but capable of short bursts of strong, powerful swimming occasionally reaching 3.9km/hr.