Fishing or global warming, what is the origin of the collapse in the number of cod in the North Sea?

Eaten fresh under the name of cod and highly appreciated by the French, cod is a species of fish characteristic of cold waters. But today cod stocks in the North Sea are literally collapsing. A team of 4 researchers led by the Wimereux-based oceanology and geosciences laboratory demonstrates for the first time that fishing and global warming are to blame.

It is a laboratory overlooking the sea, located in Wimereux, a few kilometers north of Boulogne-sur-Mer, it is from here in his small office that Grégory Beaugrand directed the research. 2 years of work which, thanks to a new digital model entitled “Fishclim”, has allowed us to show how fishing and climate influence cod stocks in the North Sea.

If the climatic regime persists or becomes even more unfavourable, many cod stocks located in the center and south of the North Sea will disappear.

Grégory Baugrand, director of research

“When you look at surface temperatures in the North Sea, you see a sharp rise in temperatures in the late 80s. The impact of fishing and climate has varied over time. Overexploitation has led to a large reduction in the stock of cod by about 77% while currently we have rather a climatic effect strongly unfavorable to the recovery of this stock, i.e. the climatic effect is of the order of 64%.” Dr. Grégory Beaugrand, Director of Research, Oceanology and Geosciences Laboratory of the CNRS/University of Lille/University of the Littoral Côte d’Opale.

And the researcher explains the climate impact on cod:

“The critical phase for cod is the larval phase, it is a phase in which it is present in the planktonic environment between March and October and during this phase growth must be quite fast but for this it needs suitable prey in its environment adapted to the larvae. However, these prey items have significantly decreased following the warming of the North Sea by about 1 degree.”

Another lesson from this work published in the scientific journal “Biology of Natural Communications” : If the climatic regime persists or becomes even more unfavourable, many cod stocks located in the center and south of the North Sea will disappear. And this regardless of the fishing quotas imposed. The international team of these 4 researchers therefore recommends adapting fisheries management to the climate.

This would allow us to have much more realistic quotas which would allow us to extend the exploitation of the stocks. We show that indeed it can be extended this way for more than 20 years and increase cumulative catches by about 30%”

In the 1970s, the cod stock peaked at 440,000 tonnes. In 50 years the temperature of the English Channel and the North Sea has risen by 1 degree. More lobster, less cod. By 2100, the fishermen of Boulogne-sur-Mer were able to witness the arrival of species from warmer waters.

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