IN A WORLD IN WHICH we know so much, why is it that we seem still to know so little? I lightly ponder this question as I warm myself under a pleasant sun and heat my core with a cup of hot tea, 16° south of the Equator.
Although it's just after the winter solstice, the water remains a balmy 27°C. Regardless of that, I am chilled from the hour-long dive.
Around me, a bustle of boats ferry recreational and scientific divers back to the diving dock at Tetamanu Village, a quaint retreat beautifully perched at the edge of Tetamanu Pass, on the southern end of Fakarava Atoll in French Polynesia. They too have returned from a dive in the pass.
The quizzical looks on their collective faces belie their thoughts. I sense that they are wondering whether I'm here to work or just for fun.
Yesterday, there were an unbelievable number of camouflaged grouper on our dive. "Around 17,000," according to Yvonne Sadovy, a marine biologist I met at the village studying the spectacle. Now, 24 hours later, one could count the number of grouper on a single hand; they had literally vanished overnight.
"It's a bit ironic." She smiled as we watched another group of divers return to the dock. "We think we know when the spawn will happen, but only the grouper know exactly when."
Sadovy was also here last year on Fakarava, the second largest atoll in Tuamotu Archipelago, which has grown increasingly popular for its unique, narrow pass, suiting the largest density of spawning grouper on the planet.
"Apparently they spawned much earlier than expected, ahead of the full moon." She chuckled. "And all these divers here today came from around French Polynesia to witness the amassing of grouper only to find that they're done with business and have left the pass!"
Ironic indeed! I too came to Fakarava, a UNESCO Biosphere Reserve, to photograph the phenomenon, in my case with a group of divers booked with Bluewater Dive Travel from Los Angeles led by photo professional Ron Watkins.
We also came to focus (literally and figuratively) on the ubiquitous sharks at Fakarava and then at Rangiroa, another atoll in the Tuamotus for which French Polynesia is famous.
Serendipitously, my dive buddy Chris Dascher and I arrived on Fakarava a day before the rest of our dive group, well before the full moon and other expectant divers. As such, we were able to manage
a handful of dives with Sadovy and a few others before the building crowds.
It's difficult to convey any sense of real perspective on what we witnessed. The density of animals within the narrow channel separating lagoon from ocean was immense. Grouper enveloped us in massive schools at the Roses, a pristine reef of tabling corals at 20m, near the entrance to the pass.
Inside, at a point where the channel narrows and the current accelerates, we tucked ourselves in at 25m between chunks of current-worn rocks to shoot ridiculous numbers of grey reef sharks at the Wall of Sharks.
"Seven hundred according to our census," Sadovy reminded me. Mesmerised, we watched them swim in slow motion into the tide.
They were clearly patient, and there for a reason. Under cover of darkness they would wreak carnage on the procreation-focused grouper.
Now, three days later, it's over and the grouper herds are gone. Their numbers thinned, exhausted and wounded, survivors have made haste to the relative safety of the lagoon until next winter's solstice.
We are now counting sharks in "dozens" versus the crazy "hundreds" along the wall, as they too have dispersed. It seems that the pass has returned to a "routine normalcy", demanding less of our frenetic attention.
Only now do I begin to really see the stunning visibility and spectacular underwater vistas Tetamanu Pass offers.
In the Tuamotu island group, it's the pass diving that draws divers from around the globe. Many of the atolls are quite large, several more than 300sq miles in area. Their internal volume coupled with limited, narrow passes to the ocean creates a special, high-current environmental transition zone between pelagic and lagoonal life-forms.
When the tide is moving, particularly on flood tides around full and new moons, the current in the pass channels can be extraordinary. On outgoing tides a smorgasbord of food sources, from plankton to baitfish, floods from the lagoon to support resident populations of apex feeders from sharks to mantas and even marine mammals.
Falling water brings reduced visibility. And while outgoing tides are certainly dived, it's the incoming tidal bores in French Polynesia that usher in the super-clear ocean water we seek as underwater shooters. During our 10-day trip we take advantage of every tide cycle, diving as much as our bodies and computers will allow.

SETTLING INTO a relaxed rhythm, we discover that Fakarava has much to offer beyond the Roses and the Wall of Sharks. One of the coolest dives we do is directly in front of the dive centre, in the pass channel at slack tide.
There, live corals dominate the sloping channel walls and transition to lanes of coral rubble and current-scoured rocks on the bottom at 25m. While there are plenty of grey reef sharks to keep us company at this site, I often trade the wide-angle lens for macro to chase rubble-loving gobies for my image collection.
Arguably among the best features of this dive are the resident schools of snapper under the boat docks, several quite tame Napoleon wrasse and dozens of blacktip sharks cruising the flats in knee-deep water.
The village also offers a unique night dive. Dascher and I made this dive sans our cameras on our day of arrival, deciding to ease into the trip after 24-hours of air travel.
Made at dark, on a shallow plateau across the channel where the current runs mild on both tides, the ever-present grey reef sharks from the pass come to the diver's lights immediately. They have learnt that the lights attract small fish, and they go after them with gusto.
I regret failing to follow up later in the trip for a night dive with my camera - the digital images taken by Watkins and others on our BDT team still have me kicking myself!
Perhaps we save the best dive for last, but not by design. Late in the week Dascher, Jan Zegarra and I have the opportunity to extend our normal drift-dive beginning with the Wall of Sharks to well beyond the dive-centre exit.
We ride the current into the lagoon as far as our air supply will take us. As the channel transitions into a wider lagoon opening, the bottom quickly shallows out to around 3m. This feature change makes for a natural venturi, accelerating the current for a considerable distance into the lagoon.
In the late afternoon sun we zoom over beautiful hard coral gardens on the crystal-clear tide. Only the occasional bommie provides brief respite from the current. and it's amusing to watch my buddies "bail out" of the flow to briefly shoot training schools of bluegreen chromis among the lush coral heads.
Too soon the week is up and it's time to move on to Rangiroa, an hour's flight north-west; a different diving experience.
The following morning Pitou, owner of Six Passengers Dive Shop, picks us up from the MAITAI Rangiroa resort. At the dive centre he gives us the skinny on what we might expect over the next few days. As at Fakarava, the dives are all related to the pass, and we will spend our time around Tiputa Pass on the north-east side of Rangiroa.
The first two dives are interesting, but with fewer sharks than we had witnessed on Fakarava they don't cause much excitement for our crew. The third dive at dusk is a different matter.
As daylight wanes, shoals of surgeonfish form and begin to move frantically 5m or so above the bottom. Suddenly, a group of several dozen fish burst from the shoal, swim at lightning speed high into the water column and discharge a cloudy mix of sperm and eggs. If you blinked, you missed it!
As the remaining light slowly leaves us, we follow the shoal with the current and try to predict the exact moment of ascension, which happens at random several times a minute.
I think I have nailed a shot or two of the moment of spawn, but a review reveals a series of smeared images. The spawners had moved faster than my rig's ability to freeze motion, even with the strobes lit for a mere few milliseconds!
The following day we're in for a treat. Pitou plans a bluewater dive for our team well outside Tiputa Pass, where his hand-held noisemaker coupled with some bait expects to raise some bigger predators.
"I'm hoping we can draw in a silvertip shark or two with the fish-heads in a basket beneath a float," he says. "They're usually the first to the bait, followed by the grey reef sharks. Give them plenty of room, let them come to you."
After dropping into hover-mode at 10m, we don't have long to wait. First to charge from the depths is a sleek 2.5m silvertip, the first I've seen on the trip.
It chews on the basket of fish-heads, which provide an additional draw to a half-dozen grey reef sharks. Strobes flash and heads spin as we adjust to the rapid, developing action surrounding us.
For an hour we remain connected, mostly with the greys, until our pressure gauges reach minimum reserve bar.
Unlike in Fakarava, the Rangiroa sharks engage directly with our team, even well after the fish-heads are gone. They swim above, below and even into our dome-ports as we track them.
As I photograph my teammates photographing sharks, it reminds me of the iconic slow-motion scene in the The Matrix in which Neo learns to dodge bullets. Weightless and nimble, my dive-mates twist, their motions dampened by the thickness of seawater as they contort for yet another image capture.
We surface to fist-bumps and high-fives as we doff gear and climb aboard the RIB, exhilarated by the encounter.
"Did you see the sailfish?" Pitou asks me excitedly as I climb aboard last. "It was swimming around you while you were handing up your camera!"
No, unfortunately I didn't. "Maybe tomorrow when we do this dive again?" Pitou's question is more of a reassuring statement meaning: you lucky dogs, you're going to do this dive again! Another round of fist-bumps!
As much as I remain interested in shooting big animals for the afternoon dive, Pitou cannot promise that the bottlenose dolphins that occasionally show in the afternoon will turn up, so
I decide to shoot macro.
Besides, it's killing me that the reef is covered with beautiful pygmy flame angelfish that are not found on Fakarava. I desperately want a good shot for my image collection.
Of course, Watkins thanks me in advance for "taking one for the team", reminding me that "we'll surely have an encounter with dolphins now that you're shooting with the wrong lens!"
And... he's right! The playful pod that have been mostly amiss with Pitou's other clients all week show up to frolic with our team for 20 minutes. I miss the wide-angle opportunities in which the rest of our divers capitalise - but I do get my shot of a flame angelfish.

ON OUR FINAL DAY we have another super experience with sharks on the bluewater dive, but don't see another silvertip, or a sailfish. On the second dive, I do have the right lens for shooting dolphins, but the five males chasing a single female, according to Pitou, do only a quick "drive-by". They have more important things on their minds…
We end the day with another treat. Pitou guides us along the pushing tide of clean, oceanic water, from the mouth of Tiputa Pass to deep inside the lagoon, in a spectacular drift-dive perhaps a mile long. The current rips and, at one point, takes our exhaust bubbles and spirals them laterally in the water column in blatant defiance of the laws of physics.
Then, from the Polynesian gods on our final dive, comes one final gift; an encounter with a magnificent 5m great hammerhead shark.
Only Watkins, our photo pro, has the presence of mind to move past our collective shock and awe to snap a fleeting headshot as we fly past the beast.
All good things must come to an end and, while none of us looks forward to our flights home, it's gratifying to know that our memory cards and hard drives are loaded with memories and even a few great images to remind us of the treasures of French Polynesia.

GETTING THERE: Several airlines fly daily from Heathrow via Los Angeles to Papeete. From there Air Tahiti flies to Fakarava and Rangiroa. Show your c-card at check-in to get an additional diver's weight allocation.
DIVING & ACCOMMODATION: Fakarava: Tetamanu Village & Sauvage, www.tetamanu Rangiroa: MAITAI Rangiroa, booking@ and for diving
Six-Passengers, which has nitrox, www.the6 Bluewater Dive Travel offers guided trips including one targeting the grouper spawn,
WHEN TO GO: Year-round but for the grouper spawn and maximum sharks go just before the full moon immediately after the winter solstice.
MONEY: French Polynesian francs
HEALTH: Nearest chambers in Papeete (two hours from Fakarava and one hour from Rangiroa)
prices: Flights to Papeete for £1500, domestic flights £335. Upcoming Bluewater trips on French Polynesia Master: 10 nights' shark-diving from US?$5400; grouper spawning/shark-dives from $5675