WE DRIFT OUT THROUGH a shallow and narrow channel at the southern end of Meemu Atoll. The current is very gentle, so I find it easy to cross from side to side, stopping to look at a moray eel, gorgonians and an anemone with resident anemonefish, then by a mound of coral where the outer end of the channel begins to open up.
Nothing is happening yet, but this innocuous hump is our reason for diving here, a cleaning station frequented by manta rays.
I loiter well to the back of the group, and off to one side. Including our guide Sylvia there are only eight of us, so its easy to see whats going on, while keeping a bit of space to my camera and myself.
A moderately large manta flies past and curves gracefully round the group, checking us out as it maintains a distance of 3 to 5m, but there are signs of something going on in the distance.
Sylvia turns my way, makes flying gestures, then holds up fingers to signal that six more rays are on the way.
The information has barely registered when the main show zooms past, like a flock of migrating geese.
The leader chooses the route, with five followers in an offset chain behind, flapping their wings and riding each others slipstream.
All goes quiet for a few minutes. Is that it This far off the beaten track, manta rays are less accustomed to spectators. Have they decided to make themselves scarce
Then two bigger mantas come through in the lead, followed by the six slightly smaller rays in formation. One of the larger ones pauses over the coral head, nose slightly up and tail slightly down, as a team of cleaner wrasse ascend to explore its mouth and gills.
The act is repeated, the flock of mantas always approaching against the current. Each time one peels off for the services of the wrasse, I grow curious about the rest of their route.
Looking the other way, I see them bank and turn high up the sides of the channel, then ride with the current and deeper until they are out of sight.
No doubt they then repeat the turn. They soon approach again from outside the atoll and into the current.
We divers are grouped either side of the cleaning station, leaving the approach and exit clear for the mantas. It just seemed a natural thing to do.
After a few circuits, with the mantas taking turns to be cleaned, they are obviously growing used to us.
Their flight path closes in and they pretty much circle where they please, twitching slightly as their undersides are tickled by our bubbles, occasionally shooting upwards in individual and formation displays of loops and rolls.

LAST TIME I VISITED THE MALDIVES, a manta cleaning station on North Male Atoll had been the check dive.
This time its the second dive for most of us, except for a couple who couldnt do the earlier check dive at Medhufushi Thila as their luggage was late. It had been left behind by the seaplane, and caught up on the next flight.
If I wasnt so tired from the international journey and itching to dive, I would have happily volunteered to ride the de Havilland Twin Otter back to Male and escort their bags.
The view of the reefs from low altitude had kept me busy, with the lens of my pocket camera just small enough to poke through the small ventilation hole in the window. I had also browsed the inflight information to learn that Maldivian Air Taxi is the largest operator of seaplanes in the world.
From the Valley of the Rays, the plan was to tour a couple of atolls further south. The mv Sheena, from Werner Laus dive centre at the Medhufushi resort, is the only liveaboard based this far south in the Maldives.
Our intended route further south really was exploratory, mixing dive sites found on Sheenas previous trips with new dives. Having said that, Im sure nothing we divers find will ever be new to the local fishermen.
So much for plans. Standing at the front of the dhoni to guide the captain to the drop-off point, Sylvia had slipped and injured her knee. She had completed the dive, but clearly cant continue with the trip, so our next dive is back near Medhufushi, after swapping her for new guide Hassan.
The change doesnt impact on the overall trip, because we are also unlucky with the sea conditions approaching the switch of monsoon.
Our intended southern exploration is redirected to tour more sheltered sites at the north of Meemu Atoll, and then on to Vaavu Atoll further north again.
Similar changes of itinerary had been dictated by the weather in the past two weeks. Earlier in the season, I am told, diving had been reliable to the south.
Hassan likes to dive channels with an incoming current, where the clearer water from the ocean concentrates everything from small fish to sharks at the entrance. This would be easy to plan with the predictable tide-driven currents of the UK, but Maldivian patterns are far more complex.
As well as tides, the circulation of the Indian Ocean, which throws all sorts of erratic back eddies as it passes between the atolls, and the wind, play significant roles in determining whether a channel flows in or out.
Sometimes a planned incoming current is actually a drift outward. On most dives our captain Harish and Hassan guess it right, but an incoming current doesnt come directly into a channel; it arrives along the edge of the atoll, then splits between the channel and continuing along the atoll wall.
As a consequence, dives begin along the atoll wall from the upcurrent corner of a channel. Divers need to be happy making negative entries and fast descents. We then descend along the buttress and drift across the channel entrance, looking for sharks in the cooler deep water. As we meet the opposing buttress, we ascend and loiter with the densest shoals of fish.
This is usually where the current is strongest, splitting between the channel and along the outside wall. Some use current hooks. I prefer to be more mobile, even if it does mean gulping air to regain my position in the current as
I loop out chasing fish. From the corner, we have instructions to either drift into the channel or along the outer wall of the atoll, depending on where the waves are breaking and it is safest for the dhoni to pick us up. We use a delayed SMB whenever there is rain or waves, with everyone carrying one, just in case.
Its a generic dive plan that works well across the narrower channels. We get the clearer water coming in from the ocean, the deep hard and soft coral of the outer walls, hordes of fish concentrated on the current-swept corners, whitetip and occasional grey reef sharks over the lip and on the bottom of the channel, and the occasional extra such as manta rays, eagle rays and dolphins.
Peering into the depth at Rakeedhoo Kandu, we see a grouper as big as a small car, barely visible in the shadows below.

A DIVE AT WHITETIP STATION is one of the very few times I have seen dolphins while actually diving on scuba. First they circled the dhoni on the surface, then, during the dive, we hear the typical clicking, though under water you have no sense of sound direction.
Crossing the lip of the channel at 30m we look in all directions - then someone gesticulates wildly into the distance.
Twenty or more dolphins are passing at the limit of visibility, their grey and white colouring blending so well with the blue of the water. A similar scene occurs several times on the dive, though never close enough for photographs.
Between dolphins, I spot a solitary grey reef shark and a whitetip. Well, the site is called Whitetip Station, though a dive at Shark Point proves shark-free, with a sting ray and a big shoal of barracuda present instead.
The sharks put on a better show at Vattaru Kandu, where the repetitive patrol of one whitetip lets me slowly edge in on the limit of its route while it gets used to me.
Through the next few dives the sharks remain sporadic and out of camera range. In recompense, I meet a few co-operative sting rays, happy to snooze as
I edge closer until my camera is almost touching them.
Also surprisingly tolerant are the brightly striped oriental sweetlips, nowhere near as twitchy as I have found them on other trips.
Many let me get to well within 1m as they enjoy the attention of cleaner wrasse wriggling through mouth and gills, blood red highlights from inside contrasting nicely with the bright yellow, black and white exterior.
We always have the dive sites to ourselves, even at the northern extent of our route at Vaavu Atoll, where Sheena shares an anchorage with liveaboards from Male at the southern extent of their itineraries.
We see their dhonis depart for dives and we go somewhere else, or simply go half an hour later and avoid the crowd. No doubt their dive guides do the same.
A welcome sign returning from the early-morning dive is a checked green tablecloth hanging across the stern of the Sheena. It means that the weather is good and we can eat breakfast outside. The tablecloth provides shade from the rising sun.
Between Cocoa Pops, sausages, egg, toast, fresh pineapple and bananas (not all in the same mouthful), we reach
a consensus that the channels at the northern extent of our route have provided less good diving than those we dived on the way.
The hard and soft coral is less vibrant, the channel profile does not provide the same rush of current and the shoals are less dense. For those interested in the bigger critters such as sharks and rays, these have been fewer and further away.
Hassan and Harish agree, and plan a loitering journey back south to look at more channels close to those that had provided the better earlier dives.
We say goodbye to Vaavu with a dive well out on the eastern extent of the atoll at Golden Wall. The channel crossing at the start of the dive follows an undercut lip with dense overhanging soft corals.
At the far corner we drift into the channel and swim the length of a sheer wall of golden soft coral. The current is by then gentle enough to allow some of us to use our remaining air, swim back out and drift in all over again.

WE RETURN TO MEEMU ATOLL via Vattaru Falhu, a sort of baby atoll between Vaavu and Meemu, to repeat an earlier dive that yielded our best sharks so far. The channel at Vattaru Kandu delivers again, though this time I stay shallow and watch from above. All these channel crossings at 30m have been slowly clogging up my dive computer, and I want to give myself and the computer the chance to fizz off.
A couple of days later, its still dark when we board the dhoni. With a seaplane to catch a day later, this early-morning dive is the only way for three of us to get a dive in and keep 24 hours clear before flying. It is our only other repeat dive, too, this time at Happy Corner, near our overnight anchorage.
The previous day it had been so good, with 20 to 30 eagle rays flapping happily past as we crossed the channel.
We dont get lucky with the eagle rays again, but whitetips and sting rays are in the channel, and large shoals of bigeye trevally congregating about the corner with, below, a tight ball of barracuda.
I surface dead on 7am. Daylight has arrived, though dark clouds suggest impending rain. My trip is over, but four of the divers have a few more days at the Medhufushi Resort, allowing them two more dives from Sheena plus land-based diving before their flights.
I watch them depart and then return from the Mantas and More trip raving about manta and eagle rays, grey reef sharks and countless whitetips.
A few days extra at the resort to follow on from the liveaboard suddenly makes a lot of sense.

FACTFILE
GETTING THERE: Flights with Emirates via Dubai, www.emirates.com
DIVING & ACCOMMODATION: Built in 1995 and modernised in 2007, the 24m mv Sheena can do 14 knots. It has two generators and produces three tonnes of fresh water per hour. Capacity is 14 guests and all seven air-conditioned cabins have private bathrooms. There is a spacious saloon and several sun decks, www.wernerlau.com. Rental equipment is available from Medhufushi Resort.
WHEN TO GO: Year-round. The driest months with best visibility are in the north-east monsoon, from January to the end of April, when John Liddiard was there. Other months have more plankton, with increased chances of manta rays and whale sharks. Air temperature is 24-30°C, water 26-30°C, so a 5mm wetsuit is plenty.
MONEY: US dollars
PRICES: Regaldive offers a weeks liveaboard diving on Sheena including return flights with Emirates from £1599, 01353 659 999, www.regal-diving.co.uk
FURTHER INFORMATION: www.visitmaldives.com