We stayed still as the manta floated, somersaulted and performed the most majestic ballet for us.

GO GO GO! YELLED ALEX FROM THE STERN. Commando-style, 10 of us leapt from the boat. There was a sea of arms and fins and a rather painful elbow in my ear as the group splashed its way into comfortable spacing, like a herd of buffalo jumping into a croc-infested river.
The sea was flat, the sun was shining and the tell-tale wings of giant manta rays were splashing along the surface almost everywhere we looked. Close cousins of sharks, the mantas are gigantic filter-feeders scooping up the tiny plankton and small schooling fish in the water column. They are one of the largest animals in the oceans, and occur around the globe in the tropics and in warm temperate seas.
There are few places where you can experience such close encounters with this inspiring creature but this was one of them - Ningaloo Reef in Western Australia. The rays were here to take advantage of the famous coral-spawning event that occurs every March and April. Along with the whale sharks, they are a major attraction for tourists.
Looking down and trying to focus in the gloom, the unmistakable shape of a manta appeared, then two more rose out of the green soupy mixture of plankton. At more than 4m across,
it was an awesome spectacle. Manta rays have been reported measuring up to 9m across, although most that we encounter are a respectable 4-5m and weighing in at around 1400kg.
The one gliding and tumbling gracefully around us was large enough to make me feel like an insignificant dot in the ocean. I couldnt help thinking of The Abyss as we watched them twirl and pirouette like alien spacecraft, oblivious to our presence just feet away.
For a creature that appears as though its barely moving, it cant half shift!
We were snorkelling today, and at full pelt and wearing good fins, even the fittest of us struggled to keep up when the rays decided to take off.
After fewer than five minutes we sat bobbing in the water, puffing and wheezing, while these incredible creatures swam effortlessly away at a deceptive speed.
We soon spotted another manta and were able to spend time with it as it performed its ageless ballet around us. This one has epaulettes, my partner Paddy gurgled through his snorkel. Must be the boss.
Individual mantas can be identified by researchers because of the distinctive patterns on their shoulders and undersides, as individual as our own fingerprints. Our manta (as I was now thinking of it) had a military-style white stripe across its shoulders.
These unique markings can also help us identify regional differences between populations and learn more about these animals. Where they go when not feeding and congregating off Western Australia remains something of a mystery. So little is known about the species that it is almost impossible to know just how commonly it occurs, or whether it is endangered.
Looking up from our private manta show, I found that Paddy and I were alone. He was head-down, 3m away, but as I swam over he looked up gleefully and gurgled incomprehensibly. I shook my head: No idea what youre saying,
I gurgled back.
He pointed to his stomach and made a sign to enlarge it. Surely he wasnt talking about diets out here in the Indian Ocean.
No, he spluttered at the surface, she looks pregnant! And indeed our manta did look pregnant.
Manta reproduction is again a mystery. I knew that, like some of their close relatives the sharks, these rays give birth to live young and have only one or two pups at a time, but no one as far as I knew had ever seen a birth.
Of the few reports, it seems that baby mantas are as oversized as their mums, measuring in at a massive 1.2m. I wondered how many pups our manta would have, and how close she was to giving birth. We stayed still as it floated, somersaulted and performed the most majestic ballet for us.
Paddy was eager to dive and get closer. Just dont touch it! I warned. Mantas have a mucous coating that protects them from marine diseases and infections. In some areas of the world where divers regularly touch mantas, the animals have developed angry skin lesions.
Down went Paddy, shrinking to toy size next to the enormous cloak of the wings. Predictably, the manta began to dive too. Grinning through his snorkel, I could see water flooding into Paddys mask as he surfaced. Just brilliant! he said breathlessly.
This is where I started to feel a little weird. As a marine biologist, I am usually quite rational about the real risks from wildlife. The boat was 500m away and I could see heads popping up around the ocean waiting for a pick-up, but the calming wonder of the manta experience had just subsided.
Whats up Youve gone pale, said Paddy. I explained as calmly as I could that I had a very bad feeling. Something was unnerving me. He, bless him, calmed me as much as he could, by using such carefully thought-out approaches as: For Gods sake, dont be so soft!
I was still worried - something in the water had changed. I felt like a buffalo separated from its group while a lion paces around.
Paddy was becoming agitated at my mounting concerns. I looked at the distance the boat was from us, and looked back down into the water.
The manta was still with us. She doesnt look worried, I thought, but how could one tell A certain furrowing of its gills, perhaps
I expected the manta to bolt at any second, and for a grey shadow to appear below us. The visibility seemed to be getting worse, and so were my nerves.
I think we should get on the boat quickly, I said to Paddy, quite calmly.
I heard the boat change direction and come heading towards us at increased speed. Get on the boat! the skipper said, as he pulled up.
No we have a manta here, Paddy yelled back.
I know, just please come back onto the boat. We were joined by an American couple who had swum over to see our manta ray. It was the mix of urgency and forced calm in the skippers voice that had us all leaping from the water and landing unceremoniously on the dive deck in a jumbled heap.
I pulled off my mask and fins. I didnt want to worry you, said Rob the skipper uncomfortably, but the spotter-plane saw two large tiger sharks heading straight towards you.
Oh, I said, giving Paddy a hard told you so look as he stared at the two dark shapes now cruising next to the boat, just metres from our private manta show.
Our fellow manta expeditioners sat opposite, still tugging their fins off. Their jaws dropped. Nice as it was to see two 3.5m tiger sharks up close from the safety of the boat, it was less nice to think that they may have been investigating us. It was about lunchtime, after all.
Of course, knowing that the rays make up the diet of tiger sharks, it was hardly surprising that a couple of peckish specimens should be attracted by the prospect of a manta snack.
I didn't like to think that they may have considered a couple of snorkellers as a starter.
The sunset accompanied us as we returned to shore, in a daze of wonder ticking off two of the biggest wildlife attractions of the remarkable Ningaloo Reef, albeit one of them being quite unplanned.
The mantas were still visible in the bay, their graceful wings flapping in the air. Still performing their ballet, but this time with no audience other, perhaps, than the tiger sharks.
I hoped they enjoyed the inspiring and ageless performance as much as we did, and could avoid the temptation to take a nibble out of the main players, at least until they had taken a bow.

Rays make up the diet of tiger sharks