Blast fishing turning Tanzania's waters into 'killing fields'

It turned out we didn’t require a boat to meet Tanzania’s blast fishermen.

We just needed to follow a motorbike down a bumpy country track to a clearing close to the beach.

It was an uncomfortable drive – but nothing to match the queasy hours we’d spent on the rolling Indian Ocean tracking these men from a frustrating distance.

Four men to a boat, two or three standing look-out and another manning a powerful outboard engine.

We watched them watching the ocean and the flocks of gulls that act as nature’s spotters for the tuna beneath the waves.

There were five or six crews out in what our local guide called "bomb central".

But only once did we manage to catch on camera the moment one detonated an explosive in the water.

And then – whatever the correct nautical term is for it – they scarpered, cranked up the motor and disappeared beyond the swell.

It was clearer than the crystal blue water that my aim of asking them some tough questions out there had, well, foundered.

But undercover of night, and far from preying eyes, two young men agreed to talk to us, and with disturbing ease show us how they manufacture bombs.

It was a well-practiced routine – and for obvious reasons I won’t give you the ingredients – but they told us they knock out 10 or so every day.

The casing was a plastic bottle. What goes inside is apparently readily available - in part thanks to Tanzania’s boom in construction.

Blast fishing is another industry, pardon the all too tempting pun, that is booming here.

In our film, we talk to a marine conservationist who estimates, with confidence, there are 50,000 undersea explosions a year.

It’s a cheap way of harvesting fish, fast.

The costs are born by a stunningly beautiful undersea environment reduced to rubble.

The coral reefs that occur along two thirds of Tanzania’s coastline face, in the words of one environmentalist we spoke to, "obliteration".

With them will go the habitat and breeding grounds for countless species of fish.

To me, the saddest section of this On Assignment are the pictures of a reef recently attacked. It looks like a battlefield strewn with fish, both dead and dying.

In the killing zone, it seems much goes to waste. Blast fishing is brutally effective, but it is not efficient.

On Assignment will be broadcast on ITV tonight at 10.40pm