Sydney, Australia

I have been studying marine biology, focusing on sharks and wanted to get closer to those that I have read about. When I finally stepped into the shark tank in Manly Aquarium and saw a very toothy grin ahead of me I felt extremely nervous but kept on walking (negatively buoyant and without fins), my scuba gear like a giant octopus against my back.

I see them now in the waters of the aquarium and not from the plexiglass tunnel like most people. I view these creatures inches from my mask, nothing except water separating me from them. Dark shapes, shadows in the murky blue, gliding softy through the water towards me. Sleek and streamlined, rows of teeth, a curved dorsal fin, the grinning slit of a mouth. Grey nurse sharks, a species nearly extinct in the wild, four hundred left to wander the seas. I felt sorry for the sharks trapped in places like this tank, swimming round and round, following the contours of the glass. That is of course till I stopped and thought about where the rest of the species are, stuck on walls or fleeing from men with nets. Even when kept in captivity they still look like what they are: Masters of the deep, a species so adapted to killing they have no natural predators. Born into the world when the eggs hatch inside the mother, the strongest pup must kill his siblings before he can leave the uterus. Once out into the world he has at his disposal a streamlined body that can travel at amazing speeds, seven rows of teeth and a mastery of senses including two that humans do not even possess.

The first is an ability to detect the electric fields given off by fish and to travel quickly to their source, a sense so acute that he can feel a twelve-volt battery several nautical miles away. The second relies on the lateral line, a long string of pressure sensors extending down the sides of a shark to the nose, with which he can feel vibrations around him. This sensitivity is most acute in the nose, and if hit there the shark will flee from any humans unfortunate enough to need to defend themselves. Attacks by Grey Nurse sharks are extremely rare however because they will only eat what they can fit inside their mouths and therefore do not register divers as food. This does not apply to a shark that feels threatened however as it will bite to defend itself, everting and dislocating its jaws to a size where it could swallow a basketball or alternatively your head.

Suddenly a massive dark shape charges into me, throwing my tank around and eclipsing the light as I stagger back. A two hundred and fifty pound Tasmanian stingray, looking like a black pancake being hurled upwards from the pan has just careened into me. Like a cat this ray is trying to get its food and its belly scratched at the same time. Looking up as she slides over my body I can see her mouth, rows of rollers designed to crunch up mollusks and crustaceans.

Usually all I think about is the past and future but there, under the water with these sharks cruising around my head I was fully absorbed in the present. This is a state I would like to be in more often - without the help of underwater predators.