28 June 2010

The toothy grin of the ragged-tooth shark

Judith Browne
Photograph by Geoff Spiby

Ragged-toothed sharks might look like they need to see the dentist, but you’re more likely to find them hanging out at your local aquarium, particularly if it’s the Two Oceans Aquarium. While they inhabit the Atlantic, Pacific and Indian Ocean, these large sharks adapt well to life in captivity and even reproduce there, making them one of the most popular of their kind in shark tanks worldwide.

Nearly all sharks have many rows of serrated teeth, ready to replace the old ones, but ragged-tooth sharks have adapted over time to grip fish and other slippery prey in their impressive splay of needle-like teeth. Raggies, as they are often called, lose and replace thousands of teeth in their 30-year lifespan.

In part because of their more vicious grin, making them victim to spearfishermen, these sharks are threatened around the world. They are slow to reach sexual maturity, are vulnerable to over-fishing given their inshore habits, and give birth to very few young.

Why so few young, when these female sharks have two uteruses and lay many eggs?

Known in Australia as the grey nurse shark, the raggie has a most unusual nursing routine. The species is ovoviviparous, meaning they bear live young from eggs that hatch inside the uterus. The young sharks develop and eat each other until there are only two young left, one in each uterus. To provide further nourishment for her young, the mother continues to produce eggs that are eaten by her two remaining young. When they are fully developed and able to fend for themselves, she gives birth to them in a lengthy labour.

This isn’t the only unusual thing about these sharks. While they can breathe underwater, they have been observed gulping air at the water’s surface. By swallowing air and storing it these sharks can hover motionless in the water, neither sinking nor swimming.

Come to the I&J Predator Exhibit and watch these smiling sharks at what seems like zero gravity or book your first encounter.

blog comments powered by Disqus