Plenty of cod in the sea?

Published: 21st Sep 2012

This week we have been following with interest the mystery of the North Sea cod population.

It started with the Sunday Times sounding the death knell for the cod, and the Department for Environment, Food and Rural Affairs (Defra) and the Centre for Environment, Fisheries and Aquaculture Science (Cefas) immediately "setting the record straight" on exactly how many cod are left in the North Sea.

Before you write this off as a story of minor importance, think of it as a cautionary tale on the press's sometimes iffy relationship with numbers.

At the heart of the matter is the newspaper's statement that "fewer than 100 mature cod are left in the North Sea." Defra replied saying this isn't correct, and there are actually around 21 million cod in the North Sea.

The author of the article, Jonathan Leake, took to Twitter to respond to Defra's call for a rectification:

So who's right? We decided to dissect the article to see how the confusion might play out to a reader.

Let's start with the headline.


Adult cod: 100
Non-adult cod: unknown

The paragraph which follows adds some context:

 "FEWER than 100 mature cod are left in the North Sea after decades of overfishing, government experts have found."

Adult cod: fewer than 100
Other cod: unknown (and it's not looking good)

By now, you might have a question floating in your head: at what age do cod reach maturity? Callum Roberts, Professor of Marine Biology at York University, can answer that question for us. He's quoted in Sunday Times article in question saying:

"Many industrial fisheries are now so intensive that few animals survive more than a couple of years beyond sexual maturity [age four, on average, for North Sea cod]."

Chris Darby, head of the team at Cefas, is then quoted in the article saying:

"Our latest assessments suggest in 2011 there were 600 cod aged 12 to 13 in the North Sea, of which about 200 were caught. None of the catches recorded at North Sea ports around Europe showed any fish aged 13 or over.

"Analysis of that data suggests there are fewer than 100 such fish in the whole North Sea."

Adult cod: unknown
Cod aged 12-13 years: around 400
Old cod (over 13 years): fewer than 100

Defra rebutted the feature and countered with their own figures:  

"We know there to be around 21 million mature cod in the north sea. Cod start to mature from a year old and are fully mature at age six. There are a small number of cod over the age of 12 years old which has always been the case in the North Sea even when fished at lower levels in the 1950s and 1960s. Cod older than 15 have rarely been recorded in the North Sea." [emphasis added]

Adult cod: around 21 million
Cod aged 12-13 years: around 400
Old cod (over 13 years): fewer than 100

It gets even more complicated when we look at how the wider press reported the number.

The Telegraph, for example, ran a story the following day headlined:

From 21 million mature cod left in the sea, we're again now left with just 100. This is out by a factor of 210,000. 

The Guardian also ran a Q&A on the topic which features entirely different figures: 

Because? We are overfishing them, of course. Left to their own devices they can live for up to 25 years. But now, thanks to decades of hauling them from the water before they have so much as imagined another fish naked, there are fewer than 300 cod left in the North Sea that are older than 13.

Which means? Which, since cod become more fertile as they age, means fewer experienced older lovers to populate future generations. Plucked from the sea in their millions by fishermen, the majority don't make it far beyond their first birthdays.

Really? Really. The study looked at 500,000 fish caught in North Sea ports across Europe and found not a single adult cod over the age of 13 among them. The figures suggest there are around 191 million one-year-old cod, just 18 million three-year-olds and fewer still aged four or over.

One year old cod: 191 million
Two year old cod: ?
Three-year old cod: 18 million
Cod aged 4+: fewer than 18 million
Cod aged 12-13 years: fewer than 100
Old cod (13 years +): fewer than 300

As a final example, a post by the Atlantic Wire features a picture of an understandably distressed cod escaping the merciless hands of a northern European fisherman:

Adult cod: 99 
Other cod: unknown

Enough fun. How many cod are there in the North Sea?

Let's go back to our primary source. Cefas pointed us to the most recent International Council for the Exploration of the Sea (ICES) report on cod (table, p. 863):

In total, the ICES estimates there are 436,900,000 cod in the North Sea. Of these, 21,200,250 are mature. The estimates assume that all cod aged 6 and over are mature, the majority of 4 and 5 year-old cod are mature, and a minority of those younger than 4 are mature.

The articles in question all have one thing in common: they lead with a catchy but misleading headline and expound on the numbers in the following paragraphs. 

This press analysis raises a one important question: Are the last paragraphs on an article as important as the headline and the first paragraph? Whatever your opinion on the subject, one thing is certain: they should not contradict each other. 

Before you heave a sigh of relief and head to the fish and chip shop, let's have a look at Cefas' final estimates of the North Sea's cod population:

Total cod: 437 million
Mature/adult cod: 21 million
Mature cod aged 13+: Estimated to be fewer than 100.

Flickr image courtesy of Derek Keats


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