Greenpeace has uncovered widespread use of illegal driftnets in the northwest Indian Ocean, one of the world's most ecologically vulnerable fishing grounds

During two weeks at sea, Greenpeace says it filmed seven ships within 50 square kilometres using driftnets to catch tuna.

Another eight vessels seen on radar were using navigational patterns that also suggested use of nets.

Nicknamed the 'walls of death' for the quantity sea life they catch, the nets were banned by the United Nations 30 years ago.