Cadmium May Be Eel-Killer

May 13, 2008 -- The European eel slithers its way more than 3,400 miles downstream to the ocean to spawn -- but cadmium accumulated upriver may make the voyage fruitless for the highly endangered species.

So finds a new study by researchers at the Centre National de la Recherche Scientifique in Arcachon, France who exposed eels to cadmium in the laboratory and found that although the eggs of cadmium-exposed eels initially matured faster in the ovaries, the eggs -- and the eels -- were more likely to die than unexposed eels.

"They show that a moderate cadmium concentration is already almost lethal to the eel," said Willem Dekker of Wageningen IMARES, a marine research institute in IJmuiden in the Netherlands, who was not involved in the new study.

The cadmium levels found in eel tissues in the experiment were less than those in eels captured from the Gironde estuary in southwest France. Even at these lower concentrations, four of eight cadmium-exposed eels died in the last three weeks of the experiment, while none of the unexposed eels died in that period. The findings appear online in Environmental Science & Technology.

European eel populations have declined sharply since the 1980s, with only 10 percent surviving each generation, and an overall dropoff of up to 99 per cent since the 1960s, Dekker said.

Cadmium exposure is certainly not the only cause of this decline, the researchers noted. Overfishing, contamination from other pollutants, and hydropower stations that act like "meat grinders" to migrating eels also pose threats, Dekker said.

The eels have a four-stage life cycle, which contributes to their susceptibility to cadmium, the researchers say. In the first stage, larvae drift toward the European coasts after hatching in the Sargasso Sea. The larvae morph into glass eels, a transparent form, which enter rivers and begin to move upstream.

The glass eels (a delicacy that currently fetches about $1,000 per kilogram) then develop into juvenile yellow eels. These can live for 10 to 20 years in rivers and streams, storing fat for their 3,400-mile migration back to the Sargasso Sea, during which they do not eat.