Sharks give us the willies. Oh, sure, many divers love to dive with them, but that's because the element of danger always threatens to line the inside of our wetsuits. For the purposes of this article, we can leave out nurse sharks, dogfish and whitetip reef sharks - they are poodle puppies. Grey reef sharks, hammerheads and the like are the rottweilers - not necessarily mean or aggressive, but get too close and they'll put the fear of God in you.
The south-west plateau at Sha'ab Rumi in Sudan is swimming with grey reef sharks. They look the part - torpedo-shaped body, serious dental work and a burst of speed that makes a McClaren F1 look like it stalled on the starting line.
Ordinarily, they meander like youths hanging around a park - intimidating, but not football-hooligan-shouting-abuse nasty. Until, that is, you get in their way.
I have dived the site numerous times and had no problems - that is, until I found a cleaning station. These are normally special places where nature waves the white flag, and predators become grannies waiting for their blue rinse.
In Sudan, the sharks stop, go almost vertical and pull their heads up to reveal a surprisingly large oral cavity. Small wrasse and butterflyfish rush from a patch of reef that looks like any other, and give them the equivalent of a dental clean-up and Turkish bath rolled into one.
Grey reef and other requiem sharks need to move about or to be in moving water so that oxygenated water passes across their gills. Most cleaning stations are swept by currents; if they are not, stopping off is akin to you holding your breath. At this one sharks stop often, but stay only for a short time.
Figuring that great experiences come to those who dare, I entered the cleaning station and waited for a shark to stop. Soon a young male cruised by, eyeing me suspiciously, unsure of what to do. He passed several times and eventually decided he wanted some privacy, so he quickened his pace past the cleaning station before turning towards me.
There was no real aggression. The pectoral fins were not down, his body didn't arch and his head didn't swing, but he charged to show his discontent. He veered left at the last second, close enough for his wash to hit me. I figured I had pushed it long enough and left. Turning to check on the shark, I saw him upright with his mouth open, enjoying a spruce-up - exactly where I had been a moment before.
It was one small moment in my life, but I won't forget it in a hurry. Sharks have that effect - try as we do to rationalise it, the underlying Jaws factor is still present. Pick up any marine life guide and the words 'potentially and dangerous' still sit together when describing many species. But that's why they make our dives so much more thrilling.

Hammer between the knees
Kevin Goodchild
Hammerheads hold a fascination for me, so when my buddy and I happened across a shoal off Angarosh Reef in northern Sudan, I wanted to get as close as possible.
Hammerheads, in my experience, are shy sharks which prefer deepwater drop-offs and keep their distance, but every so often you meet an inquisitive one.
Angarosh has two plateaux, one at 24m and the other at 40m. It was a rough day, but the six of us made for the edge of the first plateau.
The dive guide had indicated that this was a good place for hammerhead sightings and, sure enough, within a couple of seconds the faint outlines of about 10 sharks could be made out in the distance.
A couple of us, including the guide, swam out, my video camera recording the scene.
We were well out into the blue, but the deeper plateau was clearly below us and so was the guide. He called me down and, as I joined him, I caught sight of a solitary hammerhead moving over the coral. It came closer and closer. My eye was jammed up against the video viewfinder, which isn't the best in the world.
All of a sudden there was a clonk and the housing vibrated - that was the moment I realised I was deep. The hammerhead was slowly circling me.
Closer and closer she came, but I couldn't bring myself to leave.
The shark carried on around, moved up slightly, showed me its teeth and carried on circling. It moved down and that's when I managed to get the footage of it swimming between my legs. It was a very bizarre feeling, but we were both calm.
After that, it headed back out into the blue and I had to make my way slowly back to the shallows to perform some decompression. I would not have missed the experience for anything in the world.

Teething troubles
Tony Williams
This one is slightly embarrassing, but I was inexperienced, which is my excuse. It was, after all, my first open-water dive.
It was a hot, spring day and I was off Cornwall on a wreck near the Manacles. I went in with my club instructor, who led me around and, as it turned out, got me hooked on British diving.
The wreck was full of life. Although most people on the boat had dived it before, I was amazed - I'd never seen anything like it.
After about 30 minutes, we started up the shotline and stopped at 6m. I took the opportunity to gaze around and caught sight of a large shadow in the water. I studied it intently, but couldn't make it out as the visibility was bad. After a minute, it vanished.
As we started the final leg, however, it returned - and it looked huge. At first I thought it was another boat, but as my head broke the surface, I saw the unmistakable shape of a large dorsal fin coming straight for me. I was petrified for a moment, but then assumed it was someone in the club playing 'let's scare the rookie'.
I put my head under, expecting to see a diver with a cut-out fin, and came face to face with the massive jaws of a shark. I grabbed the handrail on the back of the boat and hauled myself in as fast as possible. I leapt aboard - fins, weightbelt and all - and dumped myself on the deck muttering 'shark', like the extras do in a Jaws movie just before they're snapped in half.
To my horror and amazement, everyone on the boat laughed, grabbed their masks and fins and jumped in. I thought they were mad. 'It's a shark,' I called after them weakly.
'Yeah,' said the skipper, 'It's a basking shark.'
'So?' I almost shouted, exasperated that I was the only sane person about. I was also the only diver left aboard.
'They don't have teeth,' said the skipper patiently, just as a parent might reassure a small child that a teddy bear is quite safe. I relive that day on virtually every club night.

Surface tension
Neville Widdrington
Try dives aren't the most exciting element of instruction, and the sites students visit are generally not the best. A person's first time under water is generally thrilling enough for them, without whale sharks, sea-lions and manta rays to complicate matters. So instructors often don't relish the try dive, but we do in the Canaries, where just about anything can come in from the Atlantic.
I had been at our usual site, about 10 minutes away from the port, with a couple who were rightly feeling pleased with themselves.
On the way back, I spotted a fin breaking the surface. At that distance, I couldn't tell what sort of shark it was.
I drew the boat alongside and couldn't quite believe what I saw - I was staring at a hammerhead. It was about 1.5m long and wasn't interested in anything other than a small yellow plastic bottle floating on the surface.
You very occasionally see hammerheads off some sites, but never on the surface. I think the bottle probably contained sardine oil, used by the local fishermen to attract tuna.
The shark turned in tight circles, bumping the bottle, and didn't even notice the boat stop. There was no way I wanted to pass up this opportunity, so I excused myself, grabbed my mask and snorkel and slipped in.
As I came up, the guy asked if he could join me. 'Come on in quickly,' I mumbled through my snorkel, 'this is amazing'.
As he joined me, the shark didn't falter from its yellow-bottle mission. We got within a metre, and it didn't even acknowledge our presence. Its well-muscled body shimmered in the sunshafts. I was enthralled, gobsmacked even, but unfortunately I didn't have my camera. Thankfully there was someone else to act as a witness, otherwise no one would have believed it.

Night fighter
Alan James
I love night dives. The creatures you find are so different and daytime fish are more docile and easily approached.
A couple of years ago I was in Yemen on a liveaboard and enjoyed several nocturnal diving experiences, but it was the last which remains the most memorable.
Yemen is off the beaten track and our shark encounters had been varied. I had seen plenty of whitetip reef sharks, grey reef sharks, even a tiger, which thought I was lunch, but it wasn't until this final dive that I really felt intimidated.
My buddy and I entered the water from the dive boat's rear platform. He had a few equipment problems and said he would join me on the bottom, knowing I was keen to get started and that it was only shallow.
I drifted down towards a collection of large boulders, interspersed with gravel. As I neared the bottom, I shone my narrow-beamed torch down to see where I was headed. Instead of the gravel beneath me, I saw a large grey fin, and I clipped it as the shark whipped past under my own fins, even though I had pulled my legs up. It then shot away, obviously as surprised as I was.
I regained some composure and raised my camera and strobe to see where it had gone. Shining my torch slowly around into the darkness, the light painted my new friend's grey, sleek form, circling me menacingly. I remember wondering whether it would be a safe time to fire the flash and capture an image, but before I had reached any decision or plucked up the courage, the shark turned away, its image growing smaller as it retreated.
It's gone, I remember thinking with some relief - but it hadn't. Like the bad guy in a horror movie, the 2m-long creature returned and charged my torch beam. I turned my only defensive weapon - Nikonos V with 15mm lens and old-type viewfinder - into a hammer. As the shark made contact with me, I thumped its nose and, in the process sheered the 6mm bolt holding the viewfinder in place.
My next recollection was looking up at the surface in darkness, without my regulator. I was rolling around helplessly and could see the torch on my buoyant strobe bobbing around just above the bottom.
Don't ask me my state of mind as I hugged the nearest rock and replaced my DV in total darkness. Let's just say that I was very glad I had a spare pair of swimming trunks on board.
I watched my torch bobbing on the strobe for some time, surmising that the shark's anger was directed at that rather than at me.
After a few minutes, I assumed that the shark had dealt its blow and gone, so I retrieved my equipment and shone the beam around, searching for my attacker. It was nowhere in sight. At that precise moment, my buddy arrived and gave me the OK signal. I returned with the internationally recognised shark sign and he gave me an even more enthusiastic OK sign and proceeded to set off into the inky blackness.
I spent most of the dive looking behind me, waiting for the next blow. Luckily, it never materialised.

SHARK attack behaviour
The upset shark pushes its pectoral fins downward and moves erratically. (You have the chance to swim away and avoid).

The back is arched and the movement becomes exaggerated, with the head moving from side to side. (You still have a chance to escape unharmed, but it doesn't take long to reach phase three.)

Seeing no other way out, the shark charges, often with a bite. (Ouch, you pushed it too far).
No pictures!
Matt Harris
I used to work in the Marshall Islands, which is pretty much jammed with sharks. On this particular day, I was accompanying a Thai underwater photographer and film-maker who wanted some images for a brochure. He requested a lot of shark action, so we headed for the north point of Arno Atoll, renowned for its grey reefs.
We were alone and there was a strong current - good shark-watching conditions. After a few minutes, we came across a juvenile grey reef shark about a metre long that seemed to tolerate us being close enough for photography. I left my companion, who was loaded down with a double-decker Nikonos V rig and strobes, and went off to find another subject.
At one point, I turned and saw him in about 7m, right up against the reef wall with the shark in between. I couldn't believe anyone would voluntarily trap a shark like that. The wall virtually touched the surface and he wasn't letting the shark go. The strobes were still firing and the shark was getting more and more agitated.
Then it snapped. It had had enough and wanted to show it with the classic first-stage warning - the pectoral fins went down. I started after the photographer, screaming through my regulator for him to back off, but he just carried on oblivious to me and the shark's discomfort.
I swam as fast as I could, but the shark was getting even more annoyed and moved above the photographer, arching its back and whipping its head around until it was more or less spinning on the spot.
I stopped, knowing it was too late to save the situation. Luckily for the photographer, who was still snapping away, it was only a small shark. It moved suddenly, grabbed his camera, shook it violently for a few seconds and darted off.
The upshot was a bleeding finger where the shark's teeth had penetrated his glove and a flooded camera where it had grabbed the lens and wrenched it away from the camera body.
Had the photographer backed off, he would have had some incredible shots.

The bronze whaler
Mark Kininmonth
A couple of years ago I was working as a dive instructor in Cairns on the Great Barrier Reef. The centre was similar to many others in the region, in that it offered both training and guided dives to qualified divers.
I was taking a group of three students to a popular site called Moor Reef. I had a Swiss couple and one Italian, but they spoke good English and were confident and capable in the water. It was a good day, but a slight current was running along the wall. Nothing unmanageable, but I needed to take care to ensure that I didn't lose anyone.
As it turned out, the current was the least of my worries. A group of qualified divers and their guide went in as I gave the students a briefing. We entered the water about 15 minutes later.
The dive went well, starting in the channel and running out to the seaward side. Everyone completed the exercises and had a blast on the tour, but one got low on air, so I decided to ascend next to the reef wall which, as it turned out, was quite near the surf zone.
Obviously we couldn't stay there, so I coaxed the divers out and signalled the boat, which was about 200m away. I got an OK back, but they were recovering the other divers, so we had to wait.
We were in blue water now. It wasn't rough, but after a couple of minutes I heard a muffled call from the Swiss girl. She was gesticulating excitedly. I dipped my head under and saw that we were being scrutinised by a large shark - a bronze whaler.
These puppies are often bad news, so I organised the group into a circle, with me in the middle. After all, if anything untoward should happen, the instructor should always stay safeÉ
At this stage the shark hadn't come too close, but I decided to signal the boat a little more frantically all the same.
The girl was fascinated and started to take some photographs while the shark carried on circling, its eye flicking from person to person.
To their credit, the group remained calm, possibly because they didn't know just how potentially dangerous the shark was. This helped when it moved a little closer.
Bronze whalers have attacked many times and scientists think they are attracted to splashing, which is a sign of distress or injury. A nervous person makes the right noises for a hungry shark, so I spent most of my time making sure that the students remained still.
My head moved constantly between the boat and the shark for what seemed like hours, but was probably minutes. The boat eventually turned up and the shark vanished.
For a time, I had visualised the headline: 'Tourists and dive instructor taken by shark while on a training dive,' but the shark was simply curious. Just another example of sharks not being the killing machines that people believe them to be.

Eye of the thresher
Gavin Anderson
It was long, very long, possibly twice the size of your average grey reef shark. Its enormous tail, which it would use to herd and stun small shoals of fish before finishing them off, thrust gracefully back and forth through the water as it came towards us over the reef.
Peering through my viewfinder, I could scarcely believe what I was seeing, because the pelagic thresher shark (above) is extremely rare.
I was diving with a small group of seasoned divers off the Brothers Islands. Tony Backhurst, who had organised this safari to the southern Red Sea, was just a few metres ahead and I had seen his eyes almost pop out of his head when he spotted the thresher. He was perfectly positioned to shoot some of the best video footage of his life.
My hear thumped as I wondered how long this beautiful creature would keep coming towards us. Its silvery body glistened in the early morning sun, like a well-polished classic Porsche.
It came to within 4m, and its eye, several times larger than an average shark's eye, studied us. This was one of those unique moments in a diving career, and I wished I could communicate to the shark that we meant no harm.
That eye conveyed intelligence and an unusual awareness. I couldn't imagine this shark attacking a diver though, strangely, pelagic thresher sharks are listed among the top 20 most dangerous shark species.
Our magic moment was soon over, as the thresher changed direction. Deciding to stay with it as long as I could, I swam alongside, firing off a couple of shots as it headed for deeper water.
My breathing rate was returning to normal, but no sooner had we finished giving each other exaggerated OK signals, than it all began again. A second thresher appeared, possibly disturbed by half a dozen divers yelling under water and pouring out bubbles at crazy rates.
Instead of disappearing into the deep, it climbed some 20m above us, circling like a plane waiting to land. Seeing it from this perspective showed off its design to best advantage. Gracefully it flew over us and away into the distance.

Good to meet you
Ken Sullivan
Most people equate the Galapagos with hammerheads, and we certainly had our share of close encounters on a two-week liveaboard trip there. But what stuck in my mind was what happened on the last day, at a site known as No Man's Rock, which was hyped up in the briefing as offering strong currents, massive drop-offs and large sharks. We were pretty keyed up as we jumped in.
The rock is a pinnacle in sight of the island and my buddy and I decided to circumnavigate it first.
The current wasn't that strong, so we finned slowly around the rock face, looking at the marine life that profited from the high-energy environment.
Then, as I rounded the seaward corner, I saw it: a 3m-long oceanic whitetip coming the other way. We met almost face to face.
Its classic elongated pectoral fins with their dazzling white curved ends were unmistakable. Not to be confused with the whitetip reef shark, this aggressive and increasingly threatened species will eat almost anything it can catch.
To say I was shocked was an understatement, but I wasn't alone. The shark looked surprised when he caught sight of me. I gulped, and weighed up my options. A thousand wildlife documentaries came to mind. I remembered that wild animals are fine unless you startle them - which is exactly what I had already done.
I decided that the best thing to do was to drift back towards the shore and get out of its way.
Unfortunately, the shark came to the same conclusion and we stayed parallel to each other.
Luckily my buddy, who still hadn't seen the shark, came the other way round the pinnacle. The shark dealt with the situation by calmly pulling its head around and moving out to sea.
I wasn't scared as such - concerned, yes. However, I have seen many sharks and have yet to feel threatened.


SHARK BITES: In 1808, a basking shark washed up on the Isle of Stronsa was reported to be a sea snake with a mane like a horse and six separate feet.
Hammerhead sharks have long been the fascination of scientists trying to fathom the development of the head. Popular consensus now recognises that it probably gives the shark lift and lessens the energy output required to swim.
There are approximately 350 species of shark and only a handful are known to have attacked people.
The whale shark is the largest fish in the seas and can reach more than 14m in length.
Most sharks must move to pass water over their gills and to maintain depth - unlike fish, they have no swim-bladders. Bottom-dwelling sharks, however, have the ability to pump water, allowing them to stay still for extended periods.
Sharks' sensory organs are very advanced and little understood. They have the usual sight, smell and touch, but also the ability to detect electrical signals, thanks to organs known as the ampullae of Lorenzini.
Reproduction in all shark species is slow. Relatively few young are born, some in eggs, others live. In some sharks, the sand tiger for example, the first-born devour younger siblings while still in the womb.