Thirty per cent of tinned tunas tested in a dozen countries were mislabelled or had other irregularities, according to a new report based on genetic analysis.

Some of the 50 brands sampled contained different species of tuna across the same product, or two different species in the same tin, an illegal practice in Europe.

Some tins, for example, labelled as skipjack – a plentiful tuna-like fish found in the Indian and Pacific oceans – also had bigeye or yellowtail tuna, both species with declining populations.

The independent report, commissioned by Greenpeace, was timed to coincide with the annual meeting of the International Commission for the Conservation of Atlantic Tunas, running in Paris through Saturday.

ICCAT’s 48 member states, including the EU, are charged with ensuring the sustainability of fisheries in the Atlantic.

The mixing of species and inclusion of under-sized tuna from over-fished stocks is due mainly to the use of so-called fish aggregation devices, or FADs, she said.

These man-made floating objects – some makeshift collections of flotsam, others high-tech constructs – attract the fish in open seas, where they are then caught in huge, curtain-like draw nets.

Endangered species of turtles and sharks also get trapped and die.

Once in the freezers, identification and sorting of juveniles is very difficult, resulting in multiple species in the same tin.

Destined mainly for supermarket shelves, skipjack (Katsuwonus pelamis) accounts for 60 per cent of the total.

Yellowfin (Thunnus albacares) or bigeye (Thunnus obesus), both under pressure from industrial fishing, comprise 24 and 10 per cent of the global tuna market respectively.

Thunnus alalunga, better known as albacore, follows with five per cent, while Atlantic Bluefin (Thunnus thynnus), highly prized in Japan, is less than one per cent.