Greenpeace has stepped up its fight against fish aggregating devices (FADs), a controversial non-selective fishing method, with the release of undercover footage which shows European vessels accidentally capturing endangered species such as whale sharks.

According to the influential environmental NGO, this fishing technique — which is widely used in tuna fisheries — poses a serious threat to what is known as bycatch, or fish caught unintentionally in the taking of the target species. The organization has been actively advocating against the method for over a decade.

The video released on Tuesday, which reveals the fishing practices of two French and three Spanish vessels, was edited from footage sent to Greenpeace from sailors on five tuna fishing boats in the Indian Ocean.

It shows how FADs, which are non-selective floating traps, can also attract endangered species. One scene shows a net containing short fin mako sharks, rays and turtles. The video also depicts the inadvertent capture of a whale shark, which is the largest known fish on earth, with a natural lifespan of up to 100 years. Another sequence captures the moment when a trawl net full of fish — apparently bycatch — is dumped back into the ocean.

On its website, Greenpeace hosts an interactive presentation charting the damages caused by FAD fishing. The NGO recently criticized Petit Navire, one of the leading brands of canned tuna in the French market, as one of the worst offenders.

Though the French company declined to respond to VICE News' request for a comment, in an article published by the Huffington Post, Petit Navire's Director General, Amaury Dutreil, describes Greenpeace's campaign as "simplistic and reductionist," claiming the NGO does not take into account efforts by the brand to reduce its reliance on FADs. Petit Navire claims to be designing nets with escape panels for sharks, and advocating the use of sonar to allow fishermen to selectively target appropriate fish populations.

Speaking to VICE News, Greenpeace France spokeswoman Hélène Bourges explained the mechanisms behind FADs:

"FADs are floating objects that can be more or less handmade. Objects such as buoys, bamboos or ropes are sunk deep into the water and then drift out into the open sea. Since these are the only shelters available, animals congregate around them."

The issue, according to Greenpeace, is that this type of installation attracts not just tuna, but also "[…] small fish, rays, turtles, and sharks. A whole ecosystem is recreated around the FAD."

According to Bourges, the FADs installed by the tuna vessels are equipped with GPS signals for easy tracking and sonar relays that detect the volume of fish present under the device.

"When they arrive, they surround the FAD with a seine [a fishing net that hangs vertically in the water] and bring up everything that is there. They know perfectly well that FADs don't only attract tuna. And even in terms of tuna, we know for a fact that the catch will contain many juvenile albacore, the species most consumed by the French. These are fish that have been caught before they have had a chance to reproduce."

Bourges claims that the Greenpeace crew were able to monitor FAD fishing fleets via AIS (Automatic Identification System) signals, a tracking system used on ships to identify and locate vessels. They were also able to determine which brands the boats were supplying. This is how French brand Petit Navire, which is supplied by FAD fisheries, got caught in Greenpeace's nets. Bourges told VICE News that a petition sent to the Director General of Petit Navire, calling for a ban on all FAD-sourced fish, has collected nearly 35,000 signatures.

Bourges added: "There is no magic wand, but what we do know is that consumers have a good amount of power. Nine out of 10 families have a can of tuna in their kitchen cabinet. We have already led successful campaigns in the United States, in New Zealand and in Australia."

Bourges also stressed that alternative fishing methods do exist. "Line fishing is a perfectly feasible way to catch tuna, and is a method already practiced by several brands. Purse seine net fishing on free-swimming schools, without FADs and targeting single-species schools of fish, is also [acceptable]. The problem lies in the joint use of seines and FADs."

According to WWF, more than 85 percent of the world's fisheries are currently under threat, having been pushed to their biological limits.