I am trying to slow my breathing, because they can sense fear. The shark grabs the chunk of fish, turns and ... uh-oh, it's swimming straight for me. I scramble backwards, emitting a pathetic underwater whimper. Then the animal whips sideways and disappears.
Once, if you'd asked, "Would you strap on a tank and let big, hungry bull sharks swim around you without a cage?" the answer would have been obvious. This, despite being a shark fan. I loved Jaws: the fin slicing through the water, the flashes of teeth, the mauling scenes. As a kid I read every shark book in the library.
But I must have had my rose-coloured holiday goggles on when they asked if I fancied a shark dive because I answered, "Yes please. By the way, I've only been diving once and that was just a baby dive four years ago. I had heart palpitations when I saw a turtle."
"You'll be fine," said Andrew. "Just be here early so we can get you ready."
Envisaging hours of training in a pool, I showed up at Beqa Adventure Divers in Fiji's Pacific Harbour, at 8am. Those who do the shark dive are supposed to have their open water certificate, or to have logged at least 30 dives.
But journalism can be cruel. I'm given a wetsuit and some flippers and ordered on to a boat named Predator.
Joining me are a dive-mad couple from Wellington and a deep-sea fisherman from Nelson with a great white tattooed on his back. Our dive crew includes Manasa, who will hand-feed the sharks, Eliki, who will film the action for a DVD, and Andrew, my guide. I'm the only wuss on the boat.
Beqa Adventure Divers has been operating this shark dive, renowned as the world's best, for nine years. Its owners say it's safe because the sharks have been conditioned to follow a routine. Each week, up to 1000kg of fish scraps are reintroduced to the food chain to get tourists up close and personal with the sharks.
Despite the Fijians' affinity with these animals - the shark-god Dakuwaqa is said to protect fishers from danger at sea - it's a controversial operation.
Some say that feeding sharks encourages them to associate food with divers. Others believe it upsets the ecological balance of the ocean.
Beqa Adventure Tours, which operates the dive three times a week in a marine reserve called Shark Reef, says the dive has invaluable educational merits.
With the shark population continuing to dwindle because of over-fishing,
and the shark not exactly revered as man's best friend, this is a way for people to better understand them.
Kiwi TV presenter Phil Keoghan brings shark attack victims on this dive for his show No Opportunity Wasted, to help them overcome their fear.
The fact that the late Steve Irwin has also done the dive is not such a comforting thought, particularly as he wanted to see a tiger shark, the most dangerous species after the great white.
They haven't seen a tiger since November, says Andrew during the 20-minute ride to the reef. We're more likely to see whitetip, blacktip and grey reef sharks, silvertips, tawny nurse, sicklefin lemons and bull sharks. We should also see up to 270 varieties of fish, including giant trevally, Napoleon wrasse and giant grouper.
We drop anchor and Manasa throws fish scraps off the boat. Immediately the water starts churning with trevally. The other divers jump in excitedly, and begin their descent to 32m.
After a brief training session, Andrew and I will meet them at 10m. It's the amateur version, but I'm still being thrown in at the deep end.
Any questions? "Why won't the sharks eat us?"
"They're not interested."
It's hard to believe we're not on the menu, but at 10m it's obvious we're just part of the scenery.
We kneel behind a low coral wall, in front of which the ocean drops off into an area known as "the pit". Manasa pulls fish scraps from a rubbish bin as crew stand by with metal poles.
I've never seen so many fish. The water is thrumming with thousands of jacks, snapper and trevally, swirling furiously in a spiral. A grouper with Angelina lips is the length of my leg. Others are tiny, bright yellow or blue, or striped like zebras. The fish nibble at the scraps but never get too cocky. They know the food is for the sharks.
There must be 50 of them, blacktip and whitetip reefs, a couple of greys, long, sleek and quick. They wriggle towards Manasa and grab chunks of fish from a chainmail-gloved hand. As they swim off, he strokes them like cats.
This is easy, I'm thinking. I'm breathing through a tube with sharks less than 1m away and I'm not scared. After 30 minutes I'm feeling a little disappointed that I'm not scared. But if the reef sharks are the cats, I'm yet to meet the dogs.
"Bull sharks are responsible for most attacks on humans after tiger sharks," says the guy from Nelson as we take a break before our second tank. Thanks, mate.
Andrew explains that sharks are scavengers that mostly feed on dead or dying fish, hence the thousands of healthy fish that are happy to swim with them. Most shark attacks on humans occur in shallow, murky waters when the sharks mistake their prey. Once we're in their territory, in the clear Fijian waters, we'll be easy to make out.
Still, the mood on the boat has changed. Manasa issues a warning about the tiger shark. Most divers will retreat from the water immediately if they see one. If a tiger appears, he will tap on his tank. We shouldn't panic but be aware that it will probably circle us several times. It's a curious shark.
We follow a different line until we've reached 10m and Manasa takes his place in the pit. Three grey shapes emerge. Forget the reef sharks - these guys are huge - they could rip us to shreds in a heartbeat. But it's remarkable how calm they are. The bulls approach from the left, often flanked by remoras (the tiny suckerfish that feed off their scraps), approach the outstretched fish heads, clamp their jaws around them, exposing those fierce teeth, then swim off.
Sometimes Manasa teases them, moving the flesh away from their jaws so we can get a better look. And he rubs them affectionately under the chin, or playfully grabs their pectoral fins.
For the next half an hour, we'll see about eight bulls circling within a 10m radius. Respect is the best word to describe how this feels. The bulls are meatier than the other sharks, and their movement is more graceful and powerful.
Then one of them comes at me. We lock eyes. My tank knocks against the coral as I instinctively move out of its path. I have visions of all the air escaping, of the shark ripping my torso in half and my final moment observed from inside its mouth. But it turns just as quickly as it came and vanishes into the depths of the ocean.
Back on the boat, Andrew gives me a dirty look when I ask why they don't put the Jaws theme tune on the DVD, but I still think a reminder of why we're usually scared of sharks would have been appropriate.
After all, this time the humans emerged unscathed.
Air New Zealand operates nine services a week between Auckland and Nadi. In addition to these is a weekly direct service between Wellington and Nadi and Christchurch and Nadi. For fares and schedule information go to airnewzealand.co.nz
WHERE TO STAY
You can find out about the Lagoon Resort Harbour at www.lagoonresort.com. Details of Pearl South Pacific are at www.thepearlsouthpacific.com
Beqa Adventure Divers is based at the Lagoon Resort. The shark dive goes out three times a week. Divers must be certified or have logged 30-plus dives. Divers with fewer than 10 dives must be supervised. See www.fijisharks.com
General information on Fiji is at www.bulafiji.com.
*Rebecca Barry flew courtesy of Air New Zealand and stayed at the Lagoon Resort, and the Pearl Resort, Pacific Harbour, courtesy of Fiji Tourism.