Modified: The catch goes into a net that keeps the fish alive in the water and when finished, they are counted, weighed and returned to the marsh.
Between 2008 and 2025, the Route Fishermen’s Sports Society has organized 175 standardized competitions in the waters of the largest marsh in Andalusia, and this, which may seem like another hobby, is an X-ray of how we lost the Erza, thanks to an emeritus professor at the University of Córdoba.
A curious (quite) natural experiment. Carlos Fernández-Delgado, the emeritus professor in question, realized that the fact that the rules hadn’t changed in so many days gave us a historic opportunity to compare the state of the wetlands. And he did it.
The data speaks for itself: in 2008, fishermen caught 4.6 kilos per hour. In 2025, about 1.1 kg. It is 76% less.
Interestingly, between 2008 and 2012, the catch decreased by three-quarters of kilos per year. And then it was stable, as it were; without increase or decrease. The question is, what happened between 2008 and 2012?
We know what it was. Fernandez-Delgado goes into detective mode. Analyze water quality, wetland levels, rainfall or participant decline. But none of this hides the answer: none of these factors showed any statistical correlation with fish declines.
Then he thought of the most obvious thing: the great predator of the Spanish rivers. It is true that prior to July 2011 no records place catfish in Iznazar; But it is also true that there are testimonies from fishermen who say that it was already visible in 2003. It is not clear, but (always according to Fernández-Delgado’s calculation) the dates fit and this means that when the Andalusian government started to act on the matter it was too late.
Obviously, this is not a demonstration. But observational as they are, the data seem persuasive.
The moral of this story is different. That, in the end, 91.9% of what is caught in that swamp is carp and carp is also an exotic fish. Instead of coming to Iznazar at the beginning of the 21st century, it came between the 16th and 17th centuries. But they are as exotic as catfish.
On the other hand, barbel (which is a native species) is about 8%. As we often repeat, the world changes very quickly and the decisions we make must be conscious. Another thing to do is blind.
Picture | Yulia Matuzava
In Xataka | We’ve been saying for half a century that a German introduced catfish to the Ebro, but that’s only part of the problem: the story of the fish that ate Spain.
