The awesome is par for the course in Cocos - in this case a scalloped hammerhead...

Divers can get a glimpse of hammerhead sharks almost anywhere in the tropics where there is also cold water, from Layang Layang and Sipadan in the Far East to the Sea of Cortez in the West, and even the Red Sea. But if you want to see hammerheads bouncing off your mask, go to Cocos Island.
Cocos is a lonely outpost in the Pacific, 36 hours sailing from Puntarenas in Costa Rica. Always hung with thick cloud and continuously bathed in torrential downpours, the centre of the island enjoys more than 7 metres of rain each year.
Its steep cliffs and impenetrable rainforest inspired Michael Crichton to write Jurassic Park. It was also the island where they found King Kong in the movie of that name.
Robert Louis Stevenson based Treasure Island on a true story that has seen many entrepreneurs lose their shirts seeking gold in Cocos. When the army of Simon Bolivar threatened the cities of imperial Spain, the Spanish evacuated their treasures - some would say in a foolhardy manner - using an English ship. Predictably the crew stole the cargo, but they couldnt wait to get home to divide their booty. Each took his share and buried it somewhere on Cocos Island.
The event was well documented at the time but, despite many efforts, including extensive use of modern technology, none of this treasure has ever been found. For divers, the real treasure of Cocos is under the water.
This could be described as the best diving location in the world. Why Upwellings of cold water mix with tropical surface water, providing fierce currents that can send you spiralling up or down without warning. One moment you are warm, the next you are chilled to the bone. One moment you enjoy 50m of visibility, the next you have problems reading your gauges.
A strong pair of leather-faced gloves for dragging yourself along unforgiving rock faces is essential. Neoprene gloves are torn to shreds within a couple of dives.
Look for respite from the flow by ducking into a hole in the cliff wall and you find it crowded with sea urchins. Skin being penetrated by their long spines becomes a familiar feeling.
It doesnt sound too good so far, does it Yet, tough though these conditions are for humans, they are exactly what the fish seem to prefer.

Parasite removal here
The waters around Cocos attract wandering pelagics from all over the Pacific. They congregate here to mate and get cleaned, because this rocky outpost in the eternal blue is home to barberfish that like to eat parasites from pelagics skin. None need this service more than the thousands of hammerhead sharks which queue up for attention.
Hammerheads form an ever-present backdrop to every dive in Cocos. To get close, wait near a fluttering group of barberfish. Using a Buddy Inspiration rebreather, I had the advantages of almost indefinite gas duration and no-stop times, and not a bubble to alarm what are rather skittish creatures. Lying among the barberfish, I was able to get good close-up photographs even with my super-wide-angle lens.
I was in the best diving location in the world, armed with the best equipment with which to dive it.
Hammerheads are very timid. Now and then a great dark shape, made up of thousands of close-packed big-eye jacks. would make its way sedately past the cleaning stations and frighten away the predators. Life under water is a game of bluff and strategy.
Photography is not easy in the waters around Cocos, because of the continuously varying thermoclines. Water temperature can vary by as much as 10 in a moment and this causes refraction in the water. The shapes of the sharks shiver and the divers shiver too. Many of my shark images ended up with deckled edges for this reason. Dive guides on mv Undersea Hunter told me that photographers return time and again in pursuit of elusive perfection.
Because the currents are caused by cold upwellings, they come intermittently, like gusts of wind. Swimming in these currents feels like being outdoors in a hurricane. But the hammerheads and vast schools of whitetip reef sharks enjoy surfing in them.
They also like to hole up together in convenient spots on the cliff walls, like dogs exhausted after a long chase. On more than one occasion, lying in my own Royal Box on the cliff wall, whitetips would come and huddle down with me.

Animal ambush
At one time, at Submerged Rock, I counted more than 30 in a crowded dormitory of sharks, varying from 30cm to a good 2m long. Raising my camera resulted in an explosion of activity. If only I had been diving with another Inspiration-user armed with a camera!
I always searched for an area which had an undisturbed sandy patch, indicating a sheltered spot. Located comfortably out of the flow, I was ready to ambush animals with my camera as they passed.
There were times when to raise it to my eye would subject the flashgun to the passing current and rip me from my hiding place. Once I watched a big old green turtle swimming hard towards where I waited. He battled round a headland for a full 20 minutes before giving up and allowing himself to be swept away.
As the only closed-circuit rebreather diver on the charter, I had to dive alone to use the equipment to full advantage. I often tried to rejoin the group during its safety stop, cruising on the current out in the blue, but at other times would come up on my own deco-buoy and use a very large surface flag.
I promised that I would always be at the surface exactly one hour after submerging, and the Undersea Hunter crew did all they could to accommodate me.
Going down slow
My descents were necessarily slow, too. Encumbered by a camera and the disciplines of closed-circuit, together with the less-than-streamlined effect of the big yellow box on my back, I inched my way down a buoyed line at a sea-mount called Bajo Alcyone (which was named by Jacques Cousteau after the vessel he was using). I was so slow into an almost impossible flow of water that I was in danger of meeting my fellow-divers coming back the other way, their open-circuit nitrox supplies exhausted.
The others observed my activities with amusement. I might be lying in wait, unaware that a whale shark was hovering over my head or a hammerhead almost lying on my back while enjoying the ministrations of the barberfish.
But fish interacted with open-circuit scuba divers, too. At Dirty Rock, flotillas of mobulae (from the same family as manta rays) bathed in divers exhaled bubbles, and large almaco amberjacks constantly tried to brush their own skin on the rough edges of the scuba equipment. Huge female marble rays cruised, pursued by numerous male admirers. Such were the numbers of spiny lobsters that there were places along the cliff walls where it was hard to get a hand-hold.

Action from the top
Our check-out dive was an easy, current-free experience on the sheltered side of the tiny island of Manuelita. It was a good introduction to Cocos. I must have seen 50 hammerheads, together with marble rays and countless eagle rays browsing on the seabed. Then, on the ocean side of the island, it was all action, with currents, hammerheads and shoals of jacks escorted by silky sharks.
Silvertip sharks have their own private cleaning station at Cocos. It is in 10m of water and aptly named Silverado. I saw some magnificent specimens, sadly trailing fishing lines from their mouths.
Fishing is banned in the waters of Cocos but this doesnt stop the worlds long-line fleet lying in wait for the sharks as they make their way to and from the manicurists. We pulled in a line that had drifted into the islands waters and found a dead silky shark attached. The week, before the crew of Undersea Hunter had pulled in a similar line with 60 dead sharks attached.
Many of the sharks I photographed had cuts and abrasions from close calls. One hundred million sharks are killed each year to fulfil the demand for shark fin in the Far East. The world shark population cannot sustain such slaughter.

Mv Undersea Hunter was used as a research vessel until being rebuilt in 1990 as a diving support vessel. She accommodates 14 passengers in air-conditioned luxury and carries two fast chase boats. Nitrox and facilities for those who use either semi- or closed-circuit rebreathers are available and there are two dive guides qualified to teach the use of nitrox or rebreathers. The vessel has all modern navigation aids and satellite telephone and is a favourite among film-makers such as Howard Hall.

Sea Hunter is a more recently equipped vessel with even more spacious accommodation for up to 18 passengers. It is usually fully booked well in advance. Both vessels are immaculately maintained.

A 14-day trip including flights (via the USA and San Jose, Costa Rica) and liveaboard accommodation on either vessel costs from£2400. You can find more information on

  • John Bantin travelled to Cocos with Maldives Scuba Tours Worldwide, 01449 780220


    In the strong currents of Cocos, the initial part of a dive with a Buddy Inspiration closed-circuit rebreather and a camera was a time of enormous task-loading. Thats my only excuse for what happened on one occasion.
    I would have to dump all the air from the BC fast, exhale through the nose to lose gas from the counter-lung, duck-dive down, inject diluent into the counter-lung to inhale, clear my ears, check that the camera was working properly and had not flooded, and set the appropriate mix on my three-mix deco computer.
    I would switch the Inspiration over to the high set-point for oxygen pressure (1.3 bar), inject more diluent into the counter-lung, continue to clear my ears, take control of buoyancy by injecting air into the BC and so on, all the time finning like hell to hit the right spot on the dive site, rather than be sent past it in the flow and back to the boat for another try.
    On one occasion I was distracted by my three-mix computer which, for some unknown reason, took me 11 minutes to set to the mix appropriate to my depth. At the same time I found myself within a vast shoal of big-eye jacks and whitetip sharks and shot lots of film. I spent most of my time at 28 to 30m, with a maximum depth of 34m.
    After 50 minutes the other divers followed the dive guide into blue water to do a shallow decompression-stop drift away from the massive down-currents encountered in the shallows on the reef.
    I decided to join them, but as I prepared to switch back to a low set-point (0.7 bar ppO2) on the Inspirations computer, I discovered to my horror that I could not have looked at the ppO2 display at any time during the dive, because I had never in fact set the high set-point.
    The Inspiration cannot be set up at the surface with a required oxygen pressure higher than atmospheric pressure (1 bar), so you have a low and a high set-point. You rig the rebreather at the surface at the low set-point and switch to the higher one when you are below, say, 5m.
    My mistake meant that I had done the dive not on a high level of oxygen but on a high level of nitrogen - higher than I would have had breathing ordinary air.
    If I went up now, I guessed that I would probably have missed well over 40 minutes of decompression stops. I was due to be severely bent!
    I stayed at around 7-10m and continued to breathe at the high set-point I had now set, which gave me about 70 per cent oxygen. After 10 minutes the other divers drifting above me started to ascend and climb into the pick-up boat. I had no way of telling them what a gross mistake I had made.
    So I too ascended and climbed into the boat, switching the Inspiration over to 0.9 bar at the surface (which would mean I breathed 90 per cent oxygen). I asked to be dropped back in where it was shallow but without currents. Seventeen minutes elapsed before I was able to go down and breathe a high level of oxygen (1.5 bar ppO2) at 9m for 45 minutes.
    I ascended to the surface (returning to the low set-point of 0.7 bar at 6m) over another 10 minutes, kindly accompanied by Peter Krahl, one of the guides. It was getting dark and it was not a bad dive. We were surrounded by large marble rays.
    Back on Undersea Hunter I opted to breathe 100 percent oxygen from the DAN oxygen-therapy set for 90 minutes while we decided what further action to take. I had no symptoms of decompression illness. I went back in to do a night dive with Peter, hanging from a line at the stern of the boat at 6m and breathing 100 per cent oxygen.
    I did this for another 45 minutes and ascended very slowly over another ten minutes. I still had no symptoms.
    Back in the UK, reconstructing the dive with the aid of a PC and Proplanner software, I realised that I probably did not need any more recompression once I had done the initial re-entry. But with no knowledge of what recompression was necessary at the time, I breathed for another 90 minutes off the DAN set back on board and waited for the bad news.
    Luckily, none came. I missed the next dives and 24 hours after the fateful dive I did a shallow dive to 10m for an hour with the Inspiration set at 1.5 bar of oxygen pressure.
    I got away with it. At no time did I have any symptoms of decompression illness.
    It seems that it is the routine actions that can be overlooked. Before that day I would never have believed I was capable of such a profound mistake.
    Fortunately, the Inspiration gave me the facility to do something positive about the problem I had made for myself. Inspiration-users must never fail to watch their ppO2 displays. Failure to do so can be fatal. Always, always know your ppO2.
    ... and one of the silvertip sharks that hangs out at the Silverado cleaning station
    an eagle ray reconnoitres the seabed