The first time I heard the term 'pair trawling' I thought it was actually 'pear trawling' and made some reference to a pear-shaped net. It never occurred to me that two trawlers would string a net between them. But of course that is what they do.

I've heard it compared to stringing a vast net between two Land Rovers and sweeping the African plains, catching and killing everything in its path. That sounds horrific - but in reality that's probably a lot easier for us to picture than what goes on underwater.

On the surface pair trawlers don't look particularly ominous. The Ocean Star and Ocean Crest (pictured) - the trawlers we recently tried to stop fishing - are among the smallest pair trawlers operating around the UK. Yet this pair have been observed killing dolphins in this fishery for years now.

But of course, pair trawling is like an iceberg, it's the bit you can't see below the water that counts.

The nets vary in size, but even the 'small' ones used in the English Channel sea bass fishery are about 100 metres wide at the mouth. When fishing, the net doesn't break the surface of the water - these are mid-water trawls. They are pulled through the water for several hours at a time. Last year we observed one pair with its nets in the water for an 11-hour trawl - although six to eight hours is more usual.

A dolphin can hold its breath for a matter of only a few minutes. Unlike humans, dolphins can go on holding their breath, and a dolphin trapped in a net will struggle as much as it can to break free. But in the end, unless it can reach the surface in a few minutes it will asphyxiate and die.

Check out our pair trawling animation for an explanation of how these fishing vessels operate, and what risk they pose to dolphins.

Take action - tell the EU Fisheries Minister that you want pair trawling for bass banned.

Willie, Campaigner