Will a sea bird eat a dead fish
Satire exposed: Tuna do not eat human flesh
If you read the article “SOS, food chain!” In the daily newspaper 'taz' on Wednesday, you may now swear that you will never eat tuna again. The theme of the play was the feeding of the animals - with the idea that the tuna, as a predatory fish, also eats drowned refugees in the Mediterranean Sea.
However, apart from the fact that it is obviously satire, the text is also wrong in every scientific respect. The marine biologist Christopher Bridges explained to us about his main research object: the bluefin tuna, also known as bluefin tuna or greater tuna, one of the most popular and valuable food fish.
DW: What does a bluefin tuna eat?
Christopher Bridges: A bluefin tuna is a large predator, known as a top predator, and is at the top of the food chain. It mainly eats so-called schooling fish such as herring, anchovies and sardines - everything that swims around in schools, i.e. in large numbers.
What about people as food?
That is extremely unlikely. First, because they usually feed in schools - that is, in groups of 20, 30, 40 or 50 fish, all of which are of different sizes and weights. And because they usually chase after active schools of herrings, sardines or anchovies. This is how they try to enlarge their prey. So a dead human body floating on the water is not particularly attractive to a tuna.
The 'taz' has published a (satirical) article in which it says that it is not only possible but also likely that tuna will eat people - especially refugees who try to cross the Mediterranean Sea and drown in the process. As a marine biologist who works a lot with tuna, what do you think of this?
The dead bodies are probably mainly eaten by sharks, which are after all dead matter. Or they become the prey of seabirds, who enjoy everything that floats on the surface of the water.
Tuna, on the other hand, is very picky when it comes to food. We see this in our tuna farm. The animals differentiate, for example, between fresh and deep-frozen fish. If they don't like something, they spit it out again - like frozen fish.
And one more thing about the fear of human meat from tuna stomachs ending up on our plates: Most of the canned tuna we eat here in Europe comes from the Pacific.
Some species of tuna weigh over 500 kilograms
How many tuna are there in the Mediterranean?
That's a good question, nobody really knows. What we do know, however, is that around 14,000 tonnes are allowed to be caught each year - so there are quite a few tuna swimming around in the Mediterranean. And I'm only talking about the bluefin tuna now, but there are many other species, for example the bonito tuna or the albacore tuna. Both are smaller types. So it's safe to say that there are a few million tunas in the Mediterranean.
They are mainly concerned with the bluefin tuna. How big is such a fish?
The size of the bluefin tuna varies - from around 2 kilograms in a juvenile fish to 500 kilograms in an adult. And they grow to be over two meters long.
This species of tuna is critically endangered, right?
That's right. This is exactly why we have had very strict catch quotas over the past five to ten years - and so far things have been going pretty well. We have evidence that the population is recovering, but very slowly. The quotas therefore continue to exist. In the past up to 70,000 tons of the predatory fish could be caught per year, today 14,000 tons are still allowed. The bluefin tuna remains an endangered species, but the findings of recent years show that we are on the right track:
What do you personally think of the said article from the 'taz'?
The article is very, very speculative.
On the other hand, the ocean is a recycling zone - everything is recycled. You could write the same story about dead seals or dead whales. The real chances that a tuna will actually eat something that is floating on the surface are, as I said, extremely slim. Tuna prefer live prey. The chances of human flesh ending up in the tuna can are about one in a million.
Prof. Dr. Christopher Bridges is a marine biologist at Heinrich Heine University in Düsseldorf. Here he heads the 'Ecophysiology' working group and is primarily concerned with the bluefin tuna.
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