Plenty more fish in the sea?
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Hello and welcome to More or Less on the BBC World Service, a haven of statistical straight-talking in a world of nonsense. Today we're starting with a particularly fishy statistic. The Daily Telegraph, a British newspaper, recently carried this headline. Only 100 cod left in North Sea. A dim future for cod, you might think.
Could the headline 'Only 100 cod left in the North Sea' be true?
Well, here's what Brian Buchan thought. He's a trawlerman who's been fishing in the North Sea for decades.
It made me so hungry. In 34 years of North Sea fishing, we've seen more cod this year than we've seen in the last 30 years. Then we get a headline from someone who probably doesn't even know what a cod looks like. It just makes my blood boil. 100 cod in the North Sea? More like 100 million cod in the North Sea.
It's not a trivial issue. Overexploitation and conflicts over fisheries cause major problems worldwide, so our reporter Hannah Barnes went trawling for the truth.
Well, let's start with the headline, 100 cod left in the North Sea from the Daily Telegraph. Could it possibly be true?
I don't think so. I think people are going out and catching more than 100 cod in a single net at any one time in the North Sea. So it was clearly wrong.
That's Dr Tom Webb, a leading marine ecologist. It turns out that The Telegraph took the story from another British paper, The Sunday Times, which claimed that there are 100 adult cod in the North Sea. A different claim, but still wildly wrong. Here's what happened. The Sunday Times got the story by looking at data from ISIS, the International Council for the Exploration of the Sea. And it then asked researchers from the British government's Centre for Environment, Fisheries and Aquaculture Science, or CFAS, for help with the numbers. But, to quote CFAS, the journalists misunderstood the data. For some reason, they decided to class an adult cod as over 13... But that's not million-adult cod. It's an ancient cod.
Now, we shouldn't be surprised that there are very few cod over 13, just as we aren't surprised there are hardly any humans older than 100. Here's Dr Karl O'Brien from CFAS.
Cod start to mature at ages one and two, and they're fully mature by age six. The bulk of the mature cod in the North Sea at the moment is constituted of fish which are actually younger than seven years of age.
So where did the newspaper get the idea that CODs reach adulthood at 13?
Who are the fishermen and scientists disputing the 100 cod claim?
Well, in the same article, the Sunday Times states that COD can live to 25, which implies a 13-year-old COD is merely middle-aged, looking forward to paying off its mortgage and getting its kids off to university. Dr Tom Webb thinks the journalist got that 25 figure from a website called Fishbase. He says that although Fishbase is a pretty reliable source of fish-related information, the idea that cod in the North Sea lived to 25 is, well, a bit of a red herring.
For each species, it has a front page with some headline statistics. For instance, maximum age, which for cod is given as 25. But when you delve into where those statistics come from, it's all very well referenced in fish base. And you can actually find that the estimate of 25 was not from a North Sea cod. It was from a cod in the Barents Sea. And the only estimate for a North Sea cod of maximum age is 11.
So here's a question. Given what we now know about when cod mature, just how many adult cod, as the Sunday Times had put it, are there in the North Sea? Remember, they said there are just 100. The right answer? Well, using the same data set the Sunday Times used, it's actually... 21 million.
And as for the Daily Telegraph's version... Only 100 cod left in North Sea.
Well, here's a more accurate version of that headline, based again on the same data.
Only 436,900,000 cod left in North Sea.
This could be a more or less record, the most wrong number we have ever reported. But all this raises a more general question. How difficult is it to measure fish stocks across the world and how reliable is the official data?
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