THE SHOOT: Purse seine fishing for tuna
LOCATION: Bismarck Sea, PNG
CREW: 1 x director, 2 x cameramen (Richard Wollocombe and Mike Bhana), 5 x divemasters
SETUP: Initially based on the fishing boat, with later liveaboard support

FOR PART OF THE SIXTH PROGRAMME in the South Pacific series, entitled Fragile Paradise, we travelled to Papua New Guinea to examine the practice of purse seine fishing for tuna.
True to form, we didnt just want to see it from the topside - we wanted to get inside the net.
The first stage of the shoot is to get onboard a fishing boat and head out to sea. Purse seine boats can be enormous, and ours is up there with the big boys. With kilometre-long nets, it can fish hundreds of miles offshore, and can store 800 tonnes of tuna onboard.
The fishing technique is a slick operation, and happens on a scale thats hard to imagine.
On finding the tuna, the boat does a huge circle around the school, paying out a 200m deep wall of net as it goes.
When it comes back to its starting point the two ends meet, and the tuna find themselves inside a giant column of net.
At this point the bottom of the net is still open, and its a race of man against fish to get this gap winched shut (purse-ing the net) before the fish realise they are trapped, and dive for safety.
Once the net is pursed, the tunas fate is sealed, although the net is so vast that they may still not realise their fate. This is the point at which we plan to drop in and join them - any earlier, and we could scare them and cause them to bolt, but too much later and we could miss our chance.
Closing the net is just the start of the process. Once the fish are trapped, the real action starts on the inside.
A giant winch will begin to gather the net tighter and tighter - with us and the fish inside...
OK, so from a diving perspective this whole scenario presents us with a catalogue of challenges: risk of entanglement in the net, overhead obstacles, overhead speedboats, heavy cables, lines, the possibility of angry sharks trapped inside the net - the list goes on.
But every shoot we do requires a lot of careful planning and the film crew are experts, experienced at diving in a range of conditions, and (of course) we always have to complete a thorough risk assessment.
On this shoot we also have net-diving expert Mike Bhana, who will act as a safety advisor as well as being second cameraman.
Of paramount importance is having a clear line of communication between the divers and the fishing boat, so that the net-hauling can be stopped immediately should anything happen.
We want the divers to be as streamlined and unencumbered as possible, so we settle on a visual signal, rather than comms.
A surface snorkeller will track them at all times. In an emergency the divers will signal to the snorkeller, who will pass the message to the surface-support boat. It will sound an emergency air horn and radio the fishing-boat captain.

IN RESPECT OF SHARKS, there are two scenarios to worry about: being trapped inside the net with scared or angry sharks, or being outside the net, where any shark in the area is likely to be in feeding mode, attracted by the smell and noise of the trapped and dying fish.
Tuna schools are known sometimes to be associated with mako and oceanic whitetip sharks, so we need to take this possibility seriously.
We bring along some shark billies, 36cm lengths of pvc pipe, to prod away anything that comes too close, and also a Shark Shield for emergencies, or for when we are outside the net and may not see something coming. The Shield is a device that, strapped to the ankle, emits an electric field that will repel most sharks over a 3m radius.
To reduce the danger of entanglement in the net, we streamline our first stages by covering them with a mesh net cable-tied onto our BCs.
This smoothes off the jutting edges, so that if we do contact the net we should just slide along it, rather than getting snagged.
The final precaution is making sure that all present have some seriously sharp and heavy-duty knives, in case the worst happens and we do have to cut ourselves free.
Dropping into the net for the first time is an awe-inspiring experience. Immense curtains of black mesh hang from the surface in folds and disappear ominously down into the deep blue gloom. The net is so large that laterally its just a wall disappearing into the blue.

THE FIRST DISORIENTATING FACTOR is the sheer noise of the boat. Close to the imposing hull, the din from the engine is astonishing, and the clanking and banging of machinery seems to resound through my body.
Despite all this, theres a fisherman on a hookah surface supply mending the nets. Hes wearing trainers, and pulls himself along the net with his hands, nothing more than a bubbling garden hosepipe gripped in his teeth, and tiny red swimming goggles.
Unable to equalise air pressures using his nose, his eyes bulge, and his goggles are half-full of water.
Nearby, we come across a solitary barracuda nosing around in the gathered folds of net, trying to find a way out. He seems a little concerned, but obviously is not yet aware of how bad his situation is. He swims slowly, testing the net, looking around for the way forward.
While the net is still stationary we get in close. With the surface sunburst behind it and the clear blue water, it has an eerie beauty all of its own. There are few fish to be seen, but with a net so large this doesnt mean that theyre not there.
We set out to look for the tuna. To keep some sense of orientation in the blue, we follow a line about 10m from the net edge. There are no signs of any sharks but, just as things are starting to feel more relaxed, theres a sudden loud clanking noise as the main winch cranks into action, and the net starts moving surprisingly fast. This turns my adrenaline up a notch, and puts us all on our guard.
There is still no sign of tuna, but there are a few schools of smaller fish scattered about, and I see
a small shark swimming on the outside of the net, apparently curious. Were about to go and film it when cameraman Richard and I suddenly both spot a young turtle trapped on our side - the inside - of the net.
Like the barracuda, hes swimming along trying to find his way around. He tests the net here and there and then, unused to barriers in the ocean, tries to find its edge.
Were concerned, and go in to take a look, but as we get near the net starts to close in overhead, and the back wall starts moving straight towards us.
Its not safe to hang around. We signal to get out of there and head for the safety of the middle of the net, and away from the fast-closing wall.
Just then the bottom of the net comes into sight, and we can see that there are definitely no tuna in with us. It seems were not going to get our sequence this time. Weve not been deep, so when its safe to surface we make straight for the edge of the net, and haul ourselves over.
On the outside, we immediately resume looking for the turtle. We catch up with him quickly, and its clear that hes running short of breath and starting to get worried. Swimming to and fro, trying to find a way around the net, he starts to get more and more agitated.
All he has to do is turn and head to the middle of the net to be able to surface and breathe, but as we watch him panic sets in, and instead of trying to find a way round he starts blindly trying to push through the net.
Its heart-breaking to watch but, being on the wrong side of the net, theres nothing we can do. Even if we were to try to cut a hole, in his state of utter panic he would probably bolt away from us.

SUDDENLY, JUST AS EVERYTHING starts to look very bad indeed, the surface-supply guy from the boat appears from nowhere, on the inside of the net. He grabs the struggling turtle with both hands and drags it to the surface, flinging it over the edge of the net.
As the turtle bolts off at lightning speed, relief floods my veins. Later the captain tells me that its considered bad luck to land a turtle onboard.
As dives go, its been intense - with so much going on, the need for vigilance has been constant. You have to take your chances when you can, so weve also only had four hours sleep, but its only when the adrenaline-high subsides that we feel the exhaustion. Its 6am, but it already feels like a long day as we head back to the dive boat for breakfast.
Reviewing the footage, we do have some nice shots, but were here to film tuna, so weve got a long way to go if the shoot is to be a success.

OVER THE NEXT FEW DAYS we shadow the fishing boat as she covers a lot of ground, searching for the elusive fish. Several times we see tuna bait-balls at the surface, or wide tracts of jumping fish, but the captain tells us that theyre too skittish for the boat to catch them.
Finally, on the penultimate day of our shoot, the fishermen locate a large floating tree trunk in the open ocean. These kinds of objects are known for attracting tuna and other pelagics.
Its late in the afternoon and will be getting dark soon, so they set a marker on the log and wait until morning.
At first light, the seiner is already setting her nets as we load up the dive tender and head over.
The light is still low as we drop in, and at first there is little to see. Then, looking down, I can dimly see that in the depths below there are a lot of fish.
We descend deeper and, as the view clears, the fish begin to rise. There are thousands and thousands of yellowfin tuna inside the net.
They pour up from the depths below, and pass us at speed.
Its an incredible number of big fish and, looking up, its a mesmerising sight as they whirl and stream gracefully against the blue.
The combination of the immense scale of the net, and the amazing number of fish makes for one of the most mind-blowing spectacles I have ever seen under water.
We spend some time filming the scene, but then the net starts to move, and the unease of the fish grows.
Having got the big wide shots, we work our way a little shallower, so that we are right in among the fish. Its an intense place to be - with absolutely everything in view moving, its hard to reference, and I have to keep a constant check on our depth.
Even our trusty bubbles are being taken sideways, and sometimes down, by the sheer force of several thousand tuna all moving as one. The net itself is also moving but, despite this, in the end it provides the best reference we have.
As the space gets smaller and smaller the fish become more and more frenetic, and at times the water is so densely packed that, as the fish pass overhead, they block out the light.
Things are really getting hectic, and as the floor of the net starts to rise, its time to get out of there. The fish arent so lucky, and as we film from the outside the net structure collapses in still further, and the situation turns to panic.

STUNNING 30KG FISH JAM THEMSELVES INTO THE MESH in their frenzied attempts to get away. Their gaping mouths protruding from the outside, they frantically try to gulp enough water and oxygen over their gills. Like the turtle, theyve given up trying to go around. They blindly wedge themselves further and further into the net, until they can go neither forwards nor back.
Its not a pretty sight, but as film-makers were here to document the fishing process. As things get more and more desperate for the fish, a green plume of blood emanates from the bottom of the net, where the dead are beginning to collect.
We turn the Shark Shield on and finish what filming we can until the vis drops to nothing.
Later, on the fishing boat, we learn that the catch was 150 tonnes - at least 7000 fish. Its been an incredible, thought-provoking experience.

* For more behind-the-scenes insights, and to see the team in action, look out for the 10-minute Making Of... film at the end of Fragile Paradise - programme six of the BBCs South Pacific series, which is due to be screened this summer.