'Bluefin tuna wouldn't eat human meat'

If you happened to read the Berlin-based daily Tageszeitung (taz) on Wednesday, the article entitled "SOS, food chain!" [German: SOS, Nahrungskette!] may have shocked you. It addresses the topic of what tuna fish eat, surmising that they "consume drowned refugees" in the Mediterranean Sea.

The article, however, apart from being an obvious - and quite disrespectful - satire, is also wrong when it comes to the science.

Christopher Bridges is a highly recognized marine biologist and gave us the lowdown on his area of expertise, the bluefin tuna.

DW: What does a bluefin tuna eat?

Christopher Bridges: A bluefin tuna is what we call a top predator, which sits right at the top of the food pyramid. Mostly they will be eating what we call swarm fish - quite often herring, anchoveta, sardines - anything that moves around in large numbers.

What about humans?

Extremely unlikely. First of all because they normally feed in shoals, groups of 20, 30, 40, 50 different fish that all vary in size. And they generally follow herring, anchovy or sardine shoals themselves, where they can maximize their feeding. That means that a floating body would not be very tasty for a tuna.

The German paper taz has published [a satirical] article stating that it's not only plausible but also quite likely that tuna would eat human beings - in particular refugees who drown during their attempt to reach Europe. As an actual tuna expert, do you find that indeed probable?

No, not at all. The drowned bodies spoken of here are mostly eaten by sharks, which are of course predators on any type of dead substances. Or, they will be consumed by seabirds, because seabirds of course are very keen on spotting anything that is floating on the surface of the sea. When it comes to tuna, they are extremely choosy about what they actually eat. We see this in our tuna farms that they differentiate, in particular, between frozen and unfrozen fish.

They will actually spit out what they do not like, most often the frozen fish. So I think it would be very, very unlikely that they would actually eat humans. And the other thing regarding the idea that humans consumed by tuna may end up on our plates - most of the can tuna we eat in Europe comes from the Pacific Ocean.

How many tuna are in the Mediterranean Sea?

That’s a very good question, because nobody really knows at the present time. What we know is that roughly 14,000 tons can be taken out per year, so it would be a large number of fish that are swimming around. This number is only for bluefin tuna - there are also many other species like bonitos and albacores - which are smaller tuna. So it's safe to say that there are several million such fish swimming around in the Mediterranean.

Your particular concentration is ‘bluefin tuna’ - how big is this fish?

They can range from two kilograms - that’s a very young tuna - to anything up to 500 kilograms. And they are over two meters long.

This particular kind of fish is endangered, is that right?

That’s correct. That is why we had very strict quotas over the last five to ten years, and we have a recovery plan that is going well at the present time. The indications are that the population is recovering, albeit slowly, so therefore we still keep the quotas. In the old days, 70.000 tons were allowed, and now it’s down to 14.000 tons. It remains an endangered species, but there have been good signs in the last three years that the population is starting to recover.

What did you personally think about the taz article?

To be honest, I think it is very, very speculative.

But on the other hand, I would say the sea is a recycling area. So everything is recycled. You could write the same story on dead seals; you could write the same story on dead whales. But the chances that a top predator like a tuna actually eats something that is lying on the surface are extremely small. They prefer their prey to be alive. The chances of people landing in a tuna can, thus, would be like a million to one. At least.

Christopher Bridges is a marine biologist at Düsseldorf's Heinrich Heine University. His area of concentration is bluefin tuna.