The critically endangered European eel population is facing collapse in Spain’s Ebro Delta, where populations have plummeted by more than 80% in recent years, according to a new study.
The study’s authors warn this decline may be as severe, or worse, than the crash of the late 1970s and early 1980s when overfishing pushed the species, Anguilla anguilla, closer to extinction.
“Today, I went to the field and saw two individuals. So, you think, ‘OK, the levels are dangerous, but the species is still there,’” study co-author Miguel Clavero, a biologist at Spain’s National Research Council, told Mongabay by phone. “But we have lost the sense that, in the past, there would have been 30 or 40 eels.”
The study pulled decades of data from traditional fisheries and monitoring programs in the Ebro Delta, a key Mediterranean wetland. Researchers found a 90% population decline in lagoons and 80% in marshes over the past 14 years.
Once abundant across Europe, these eels play a critical role in freshwater ecosystems. In many Iberian rivers, they’re the only predatory fish, helping regulate prey populations. They also serve as a key food source for otters and many bird species.
Overfishing remains a primary driver of the species’ ongoing collapse. Despite years of conservation warnings, eels continue to be commercially exploited as their scarcity has driven prices up, creating a profit incentive to harvest more.
“What is really needed, urgently needed, is to stop the commercial exploitation of the eel,” Clavero said, adding that current populations are below previous worst-case scenarios.
Invasive species may also be accelerating the decline. The Atlantic blue crab (Callinectes sapidus), first detected in the Ebro Delta in 2012, is a voracious predator suspected of preying on young eels. The wels catfish (Silurus glanis), another invasive species, has also been linked to eel losses.
Unlike many fish species, European eels belong to a single population. They all spawn in the Sargasso Sea in the Caribbean. The larvae then hitch a ride on the Gulf Stream back to Europe, where they live in fresh and brackish water for most of their lives before returning to the ocean to reproduce and die.
“Because they all reproduce in the same area and there’s no genetic structuring, eels can end up either in Norway or Morocco and have the same parents,” Caroline Durif, a senior researcher at Norway’s Institute of Marine Research and expert on the European eel, who wasn’t involved in the study, told Mongabay by phone.
According to Durif, numbers of young eels migrating to Norway dropped from tens of thousands to as few as 200 per year. “The more time series we have from everywhere in the distribution area, the better. Levels are so low now that it’s hard to see that it’s still decreasing,” she added.
Banner image: The European eel population has declined by up to 90% in Spain’s Ebro Delta. Image courtesy of Miguel Clavero.
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