After dark
Divernet
Why dive at night To see the animals in their night-clothes! says John Bantin, who takes us through the essential guide for nocturnal divers. We also hear from four Diver contributors on favourite dives made in the hours of darkness - from a transformed Scottish rock to the unknown creature of Belize, and from a virtual paddle in Bermuda to a return to the womb in PNGBELIZE BASS ROCK PAPUA NEW GUINEA BERMUDA

The underwater world takes on a different complexion at night, and that isnt only because you see things differently. Lighting up the details of the reef with your underwater lamp reveals the marine life in a full spectrum of vibrant colour that you would never see during daylight hours. Thats because everything is illuminated by daylight, filtered blue as it passes through many metres of water.
     But many of the animals take on a different colour scheme at night, too. Its as if they know that none of the other animals can see them properly. Many fish hide in the reef - parrotfish by building themselves a protective cocoon of mucus - while the nocturnal hunters are out looking for a meal.
     And it isnt only the whitetip reef sharks and the moray eels that hunt at night. Crinoids such as triffid-like basket-stars and featherstars creep from their daytime hiding places to feed on the planktonic soup. Its at this time that the coral polyps come to life, protruding from the hard corals, waving their hungry arms.
     Strangely enough, many of the more skittish fish seem unaware of divers with lamps at night, and they will seem mesmerised by your torchbeam. Others, such as the groupers in the Caribbean and the whitetip reef sharks of the Maldives and of Cocos, have learned to take advantage of this rabbit-in-the-headlights syndrome to make their hunting easy.
     How often do macro-photographers find their subjects mysteriously disappearing from their viewfinders, as opportunistic predators literally suck their victims out of the shot
     Rays feeding, hawksbill and green turtles browsing, goatfish probing for their supper in the sand; all are commonly encountered at night. Its also during the hours of darkness that the octopus stalks its prey of unsuspecting shellfish, and crabs and lobsters parade out in the open.
     Then there are those animals that are particularly sought-after by night-divers. These include the flashlight fish in the Indo-Pacific, the rosy-lipped batfish of the Galapagos and Cocos islands, and unbelievably vividly coloured Spanish dancers.
     Night-diving is more fun if you do it well, and that means making use of specific techniques. But first you need to have mastered the basics.
     When you first go night-diving, it is loss of spatial awareness that presents the greatest challenge. At times it can be difficult even to know which way is up!
     Unable to make a visual check on your whereabouts, you need to rely on your instruments to tell you how deep you are and in which direction you should be going.
     Control of buoyancy is essential unless you are diving over a fixed-depth bottom, because when its dark its easy to go deeper than you intended.
     If you are a confident diver none of this should be a problem, but anyone still flapping is probably not yet ready to dive in the dark.
     Finding your way around can be difficult for any diver, however. You suddenly get to realise how much you rely on your eyesight. Its one thing to follow a wall or cliff, but once out on flatter terrain, odd things can happen.
     I remember with fondness one time when my wife and I gently made our way in the dark from the shore out to our liveaboard dive boat. We kept meeting a group of fellow-divers. They would cross our path, appearing out of the darkness at right-angles to our route. Someone was going round in ever-widening circles, and it wasnt us!
     Using a compass in the dark can be fraught with difficulty, because you cant always tell immediately if the needle or compass-card has jammed. You must constantly recheck for this.
     A reliable lamp is essential, and you should always carry a back-up, stowed ready for use. Any lamp can fail as a result of flooding, running out of charge or simply by blowing a bulb. There is a huge range of lamps with a variety of features from which to choose, but the vital difference is between having one that functions and one that doesnt.
     Our eyes have an amazing range of sensitivity and can adjust to suit whatever light is available. Thats why the actual brightness of your underwater lamp is almost irrelevant. However, if your buddy is using a lamp of a very different output to yours, one of you is going to feel as if he or she is travelling in the dark, so try to match each other as far as possible.
     That said, underwater lights are available in a wide range of outputs and burntimes. They can run on replaceable dry cells, or rechargeable nickel-cadmium or nickel-metal hydride batteries. Generally, the bigger the battery, the longer the burntime for the same wattage of lamp.
     This is complicated because there are different types of lamp. Tungsten bulbs give a comforting warm light, while more expensive HID lamps give a cold bluish light in a far greater quantity (watt for watt), which penetrates the water further. Reflectors can give a wide, soft beam or a selective narrow beam.
     Brightness is not always an advantage. I can remember trying a new, high-powered, high-voltage HID lamp with a very wide beam and ruining the night dive for all the other divers with me. It was so bright, all the animals thought it was daytime!
     How you use you lamp is important. Shining it into the eyes of other divers is not clever because it causes them to lose their night vision temporarily. Head-mounted lamps are especially guilty of causing this effect, because you blind everyone you look at.
     Instead, shine your light on to the signal you are making with your hand.
     And keep your lamp steady. Slowly and carefully pan it round to get an idea of where you are and what there is to look at. If you wave it so that it flashes across the field of vision of other divers, it will attract their attention.
     If you want to take photographs at night, its a good idea to attach a lamp to your strobe so that you can see where your camera is pointing - unless it has its own built-in aiming light, that is.
     Moving on from lamps, ensure that your kit is rigged in such a way that it cannot snag on anything. A carelessly dragged octopus-rig or high-pressure gauge can cause a lot of problems if either gets jammed into a crevice and impedes your progress.
     Can you read your gauges in the dark Fortunately many diving computers now have their own integral lighting - providing you know how to operate it.
     Wear a full suit at night, even if its only a skin in the tropics. This is because of the danger of bumping inadvertently into hard or unforgiving objects, and the fact that stinging jellyfish such as sea-thimbles can be attracted to your lights.
     In fact, in some waters you will start to see masses of planktonic animals gathering in your torch beam, and many of them would prove unwelcome visitors in any personal orifices. How do you get rid of them Occlude your light by holding it against your body, or by putting your hand over it, and move on.
     Why occlude your lamp if you want to lose its light, rather than simply switching it off Because a bulb is most likely to fail during the initial current surge when it is switched on, so its best to switch it on when you enter the water and keep it on until you have surfaced and been picked up or climbed out of the water.
     Besides two underwater lights, its sometimes a good idea to wear an illuminated marker of some sort.
     Chemical glowsticks were favourite once but small LED lamps that run on long-life lithium batteries are becoming more common. By tying such a marker to your BC or tank valve, you can be more easily identified by your buddy and wont end up surfacing with a person other than the one you went in with!
     Some divers use permanently flashing strobes. These have not been proved to cause epileptic fits, but they can certainly be a source of irritation to other divers.
     If you need to use a surface-marker buoy at night, you can fix a beacon such as an LED light to it, but generally pick-up boat coxns will know where you are without this aid. They will see the green glow from your light under the water.
     If you need to get back to your starting point, whether it be a moored boat or the shore, its always a good idea to mark a route on the way out. This is when properly secured flashing-strobe beacons come into their own. You can usually see their light even if there is some obstruction between you and the beacon.
     Inexperienced dive-guides sometimes expect divers to make all sorts of complicated signals with their lamps when they surface.
     Experienced guides know that because divers are bobbing about on the surface waves, they can expect only one or two signals to be reliably delivered. So a steady light means come and pick me up when you can. A frantically waved light means that you have an emergency situation.
     If you are picked up by dinghy, RIB or panga, dont shine your light in the eyes of the boatman.
     Turn off your lamp as soon as it is safely aboard and keep it turned off. He may need to pick up other divers and he will certainly need to navigate. A bright light within the boat will ruin his night vision.
     Underwater lights are rarely looked after in the way that they deserve. Batteries should be fully charged before use or, if they are dry cells, you should try to keep a record of how long they have been used for.
     If you need to break open a lamp to charge it or change the batteries, be sure to check the sealing O-rings for cuts, dirt or hairs, regrease them and replace them if needed.
     And always start a dive with a fully charged lamp. With luck, you will never need to resort to that back-up light.

Night
Night is the time for Spanish dancers - this one is in Komodo.
Crustaceans
Crustaceans dance by night too - theyre all out in the open.
Basketstars
Basketstars which hide during the day come out to join the nocturnal parade
Night
Night is a good time to settle down and look closely at habitats such as anemones provide
Whitetip
Whitetip reef sharks hunt by night in some numbers at Cocos.
Sting
Sting ray in the Maldives
A
A timid blue-spotted ribbontail ray, disturbed on a night dive.
BELIZE BASS ROCK PAPUA NEW GUINEA BERMUDA



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