Loggerhead turtle caught in the net of a purse seiner. 12/04/2009 © Alex Hofford / Greenpeace

Greenpeace has taken drastic action to highlight overfishing which is driving the decline of tropical tunas and killing a range of other marine species. The use of man-made floating objects called Fish Aggregating Devices (FADs) in conjunction with purse seines – a curtain of fishing net which is drawn into the shape of a bag made for catching schools of fish – dramatically increases bycatch.

A shocking video, secretly supplied by fishers on board Spanish and French industrial tuna fishing vessels, reveals huge numbers of bycatch such as sharks, turtles and rays killed during the commercial fishing trips aboard ships which supply some of the major European brands of canned tuna, including Petit Navire in France, and Princes and John West in the UK.

"We selected the strongest images from hours of footage," said Hélène Bourges, a Greenpeace oceans campaigner in France, "The video exposes the bycatch of non-target species, being caught and dead or dying, thrown back into the sea."

She points to FADs as the primary cause of this intolerable increase in bycatch for the industry.

Fish aggregating next to an illegal FAD. 11/06/2012 © Alex Hofford / Greenpeace

A FAD is a floating man-made object used to attract tuna, but it also entices a large range of other marine life. Once a mini-ecosystem has aggregated around a FAD, industrial tuna nets, several kilometres long, are deployed. They take everything from threatened species of sharks to large numbers of juvenile yellowfin and bigeye tuna.

FADs are increasingly used by the tuna industry to target skipjack tuna for canning – about 60% of tuna are now caught this way.

Globally, FADs generate 3–6 times more bycatch of non-tuna species than the same fishing method without FADs.

When it comes to tuna species, only about 60–70% of the catch are skipjack, the rest are bigeye and yellowfin, the vast majority of which are juveniles. While skipjack populations around the world are relatively healthy, most yellowfin and bigeye stocks are not. For example, below 20% of bigeye populations on both sides of the Pacific remain. While some of these juvenile tuna are kept for canning, a considerable number are thrown back overboard. The estimates for all the tuna, sharks, billfish and other fish discarded by vessels using FADs is over 100,000 tonnes per year, or enough to fill 625 million tuna cans.

Purse Seiner Fishing in the Indian Ocean. 04/15/2013 © Jiri Rezac / Greenpeace

Too many major tuna brands are still using destructive FADs. According to Petit Navire, one of the companies who source their tuna from the vessels featured in the footage, approximately 7% of what their ships take is bycatch, but this doesn't include juvenile tunas.

Parts of the fishing industry already recognise that FADs are a problem. They are trying to limit the number of FADs to 150 per boat, and some are fishing 'free school' without FADs. Disappointingly, others (including some Spanish ship owners) do not limit the use of FADs, and can deploy up to several hundred per vessel.

There are currently very few regulations limiting the use of FADs and so downstream industry stakeholders, such as canned tuna brands, have a crucial role to play. They must commit to sourcing only FAD-free caught tuna.

MW brands, which own a variety of tuna brands, has made this commitment for its brands in Italy and the UK, but not for Petit Navire in France.

"We calculated that the volume of bycatch generated to supply Petit Navire, the leading brand in the French market, is around 2,000 tonnes per year," said Hélène Bourges.

Greenpeace divers display a banner by a fish aggregating device, or FAD. 11/22/2011 © Alex Hofford / Greenpeace

The eight recognised species of 'true' tuna are Atlantic bluefin, Pacific bluefin, Southern bluefin, bigeye, yellowfin, albacore, longtail and blacktail, and there are a further eight species in the extended family that are normally called 'tuna', including the skipjack tuna commonly found in cans.

We need your help now to stop the devastating pillage of our oceans.

Lyn Drummond is a Media Specialist at Greenpeace International.