IT FIRST HAPPENED during a morning dive in the Philippine island of Cabilao. The water was clean, interwoven by a tangle of sharp sun-rays, when a dark silhouette appeared, approaching me directly.
It was an exciting experience, which I enjoyed as a spectator, not as a photographer. My camera had a macro lens fitted, ready for an appointment with a blue anemone with clownfish, so I didn’t even bother to look into the viewfinder.
Things quickly went crazy, with divers screaming into regulators, the divemaster knocking repeatedly on his tank and divers fin-kicking in a vain bid to keep up with the giant.
Bubbles were bursting everywhere, and when the encounter was over we triumphantly raised our arms and high-fived each other.
Over the years I was lucky enough to find myself close to these giant filter-feeders several times, but never for more than a few seconds.
Yearning for a giant shark adventure, I found myself browsing jaw-dropping photos of a whale shark aggregation off Isla Mujeres.
This couldn’t be true! Everything else had to wait – I was off to Cancun!
Flying to this part of Mexico from Europe is not the most demanding of trips. A fast ferry brought us from Cancun jetty to the Island of Women (as Isla Mujeres translates), in under 20 minutes.
Loading the luggage into the cab, I was already searching for any signs of whale shark madness on the island. I was so excited that I almost expected sharks to walk among the crowds on the streets, or at least to breach above the surface of the sea.
Experience in underwater wildlife photography has taught me that inflated expectations result in disappointment. But I had seen the photographic evidence, and couldn’t wait to hit the water.

NEXT MORNING, SHORTLY AFTER DAWN, the small boat Lilly M left the jetty carrying six eager snorkellers. Two powerful engines would guarantee a quick transfer, plus the ability to explore a large area of sea. No one knew exactly where the whale sharks would be feeding this morning.
Whale sharks are pelagic shark species living in the open sea. They migrate over long distances – transfers from Africa to Australia have been reported. They are solitary creatures. But why do they gather off Mexico’s Caribbean coast in such big numbers
The answer is simple: food. During the summer months, bonito tuna spawn in these waters. In the night, females release eggs and males roe into the water. The eggs are slightly positively buoyant, so rise slowly to the surface to form a plankton delicacy that whale sharks can’t resist.
The result is an aggregation unparalleled in the world. Hundreds of sharks feed over a surface area of a few square kilometres, and in clear blue water! This combination distinguishes the Isla Mujeres phenomenon from those of Donsol in the Philippines, Ningaloo in Australia or La Paz on Mexico’s Pacific coast.
While Lilly M is cruising the quiet sea, we scan the horizon for any sign of whale sharks. Pinpointing them took longer than usual that day, but with the help of other boats we come across a large group of animals.
The water is boiling, as sharks harvest the plankton near the surface, their wide-open mouths partly protruding above it, followed by big dorsal fins, and finally the flag-waving tail fins. The scene resembles a busy port for small vessels.
For us six snorkellers, seeing this phenomenal concentration for the first time, it was almost unbelievable. Sharks swam in groups between ships, between snorkellers, between each other.
Everywhere I looked, I could see the dark shark fins. Incredulously, I twisted my head this way and that – then jumped in.
Seeing a whale shark under water is always a fascinating experience, but one that is usually momentary, followed by days, months or even years of waiting for the next one.
Here it felt quite different. After the initial face-to-face encounter, I was still looking at the camera display to review the first shots when I realised that another giant was rushing straight at me.
I was trying to get the best possible position from which to photograph it when another shark approached from behind. There were incursions from all sides.
At the same time, these animals were so respectful to the others also wanting to enjoy the bonito plankton that collisions were rare. The sharks elegantly avoided snorkellers, boats and each other.
Occasionally there may be a collision with a small boat, or a careless snorkeller who doesn’t respect the animals’ need for living space, but otherwise man and beast can co-exist in peace.
Only two snorkellers are allowed in the water with a locally certified whale-shark guide at any one time, so we were split into three groups, jumping into the water at 15-minute intervals.
Sometimes there was no need to swim, and at others it was necessary to turn on full-fin propulsion to gain a good position.
Climbing the steps into the boat after round one, grinning from ear to ear, I still couldn’t believe what was happening.

IF THE CONCENTRATION OF PLANKTON in the water column reaches a certain high level, some sharks remain anchored motionless at an angle of about 45°, tail frozen and mouth at the surface, gulping in gallons of water at short intervals and filtering the bonito spawn.
This very rare phenomenon, called botella feeding, can be observed at Islas Mujeres. While it is going on, the animal seems to be oblivious to its surroundings.
After noon, fully fed sharks begin to move into deeper water. Then, at about 1pm, they finally all disappear from the surface and can no longer be located from the boat-deck.
Our opening day ended with the tally of which every lover of the underwater world dreams – dozens of intensive encounters and hundreds of nice shots. Lilly M was the last of the daily boats to leave, and carried six of the most tired but satisfied snorkellers under the sun.
Sipping mojitos, we enjoyed the late-afternoon atmosphere under the palm trees and finished the day with dinner at a Cuban restaurant.
When dealing with nature, the most beautiful things can go wrong miraculously fast. Hurricane Ernesto had been hurtling uncompromisingly through the Caribbean and seemed set to hit north-eastern Cancun with some force. Whatever happened, the memories and images of that day could not be blown away.
The next day Ernesto shrouded the sky in thick black clouds and blew in at 70mph. It wasn’t life-threatening intensity, but it put paid to any thought of sea trips for the next three days, so we decided to explore the island by golf cart.
The south end offered a nice view, with big iguanas lying atop steep rocky walls, and we found a beautiful sandy beach with palm trees near the northern tip, albeit coloured in shades of grey thanks to Ernesto.
On our last day the wind calmed down. We set off to sea and hoped for a miracle, but the conditions had changed dramatically. After several hours of searching, we managed to find some feeding whale sharks but the waves were still high and the visibility poor, leaving us with a very different impression.
Was it worthwhile to come over for a single day of swimming with hundreds of whale sharks in clear water Absolutely!

FACTFILE
GETTING THERE: Fly to Cancun via Miami with BA from London Heathrow
SNORKELLING: Daily tours from Isla Mujeres, www.islamujeres sportfishing.com
WHEN TO GO May-September, July-August (whale sharks) are the peak seasons. August-October is Caribbean hurricane season but last year only two stronger storms reached Cancun, and such storms are rare there.
MONEY: Mexican pesos, US dollars.
LANGUAGE: Spanish but English widely spoken.
PRICES: Dive Worldwide has packages to Puerto Aventuras resort south of Cancun for ocean and cenotes diving which include day trips to snorkel with the whale sharks for £150 on top of a starting price of £1695, www.diveworldwide.com
FURTHER INFORMATION: www.visitmexico.com