For millions of years the giant bluefin tuna has been one of the most successful predators in the ocean.
But serious overfishing is threatening to wipeout the species.
Stocks in the Mediterranean have now fallen close to a level at which the tuna will be unable to breed.
The World Wildlife Fund warns that bluefin tuna could disappear from the Mediterranean within three years.
Scientists are now beginning a tagging process to work out if anything can be done to save it.
Al Jazeera's Nick Clark reports from the Catalan coast in Spain.