Fish are a vital source of protein around the world, but there are ever more fishermen chasing ever fewer fish. Most wild fisheries are at, or near, breaking point and it is estimated up to a third of all fish are caught illegally, feeding an underworld of crime.

We find out how the growing pressure is leading to violent clashes on the high seas and joins an Indonesian coastguard patrol chasing and shooting vessels out of their waters. We ask Interpol how it is trying to police the oceans and find out how illegal fishing is tied up with a criminal underworld of drugs and human trafficking.

Plus, experts tell us what consumers should look out for, and we discover fish farming may not be the answer to the problem.

(Photo: The Indonesian Navy blows up the illegal fishing vessel the MV Viking in the waters of Tanjung, West Java, 2016. Credit: Antara Foto, Reuters)