Yesterday, having sailed across more than 1,000 nautical miles of beautiful Pacific ocean, I witnessed a very ugly and clinical marine massacre by the world's largest tuna fishing vessel. Since we left the Taiwanese longliners two weeks ago, some of you have probably been wondering why we've been relatively quiet. I wanted to write about it and build up the excitement as we searched for the world's biggest tuna destroyer - Albatun Tres - a Spanish purse seining vessel. But I couldn't reveal anything as we needed to keep it all secret so we could take them by surprise. We found them on the 22nd of May but they took off at high speed and we had to chase them.

Five days later, in the early hours of Tuesday morning we found them again close to the Phoenix Islands in Kiribati where they looked like they were fishing. As soon as the sun started to come up we got into the inflatable boats and headed off to catch them and try to prevent them from netting any tuna. Our photographer and videographer went up in the helicopter to document the action from the sky and I was entrusted as the photographer on the water. This placed a huge responsibility on my shoulders as I would be the only one on the water taking pictures but I rose to the challenge with enthusiasm, duck tape and sandwich bags (official camera waterproofing issued by Greenpeace!).

It was very surreal to finally arrive next to the enormous fishing vessel, known as a 'super super seiner' due to its size. It is 115 meters long and can catch 3,000 tonnes of tuna in one fishing trip. Before seeing it with my own eyes - I found it hard to believe that such a fishing vessel existed. But even more shocking to me than the size of the ship was the vastness of the net. They were already hauling it in when we arrived but its circumference was still about as big as a football stadium! Sadly, we had arrived too late to stop the net from being closed.

It was very quiet and serene on the surface and all we could see were the yellow floats on top of the water like a giant necklace. We couldn't see any fish and had no idea of how many were caught inside the net. Raoul, our 3rd engineer on board, arrived on a jet ski and pulled a 25 meter long banner across the inside of the net saying "No Fish No Future". Usually I hate jet skis but they are really useful for something like this as there are no propellers to get entangled in the net.

While the banner was going out I was leaning over the bow of the inflatable trying to get the best possible pictures and I started to fall overboard but Adrian, our second mate and boat driver grabbed my life jacket and pulled me back safely. I dread to think about how I would have felt to have gone in the water, killed my camera and lost all the pictures! Thanks Adrian!

It didn't take very long before the net was pulled in alongside the Albatun Tres and the only part left in the water was holding all the fish. At this point I started to see the tuna jumping up out of the water at the surface but still couldn't tell how many were inside. The water in and around the net began to turn a dark shade of red as a large scooper was lowered down into the frantic pool of fish and pulled up again - full to the brim with over a thousand tuna (approximately 2 tonnes). I felt shocked and angry each time they dropped the scooper into the net and brought it up again, equally full as the time before. The fish were immediately dumped into a hole on deck that presumably led to a massive freezer. They did this again and again - maybe between 8 to 10 times - until the net was nearly empty and then they pulled the remainder on board. In just 30 minutes we had witnessed many thousands of tuna vanishing from the Pacific ocean and into a freezer.

I got back on the Esperanza around 8:30am and sat down in the mess for breakfast after changing all my wet clothes. Had it not been for everyone else around me talking passionately about what we had just witnessed I probably would have sat there wondering if it had all just been a horrible dream.

I have never seen such a sleek and sinister fishing vessel like the Albatun Tres. It can travel at 19 knots and has state of the art equipment that enables it to wipe out a school of tuna with great ease before swiftly moving onto the next. It can catch twice the amount in one trip than some Pacific island countries catch in an entire year. It is just one in a fleet of similar sized Spanish vessels that poses a significant threat to the sustainability of the tuna fishery here. We're working on getting vessels like these out of the Pacific and into the scrapyards where they belong in order to reduce the amount of tuna disappearing from this fragile region.

Read the news story to find out more.

Slideshow images © Greenpeace/ Paul Hilton and Lisa Vickers