Metal pollution is toxic for endangered eels
BIOPIX .DK /J. C. SCHOU
Baudrimont explains that as the eels burned fat while swimming, the cadmium previously stored One of the world’s most bizarre tic that fully mature European was released and accumulated in creatures is vanishing. Freshwaeels have never been caught in the the ovaries. The cadmium may be ter eel populations began crashing wild. directly toxic to reproductive tisworldwide in the 1980s. The de“We have shown that eels consues, or it may alter hormone levcline has been rapid, and scientists taminated by cadmium are not alels. Either way, she says, the eels think eels are probably succumbways able to stock sufficient lipids appear to spend part of their ening to a variety of ills, including to migrate,” says study coauthor ergy reserves detoxifying the cadoverfishing, habitat loss, polluMagalie Baudrimont of the Unimium and cannot develop fully tion, and eel-chewing hydropower versity of Bordeaux (France). The mature gonads. turbines. “That’s an absolutely clasThe European eel (Anguilsic demonstration of an la anguilla) is a prime examendocrine-disrupting comple. The number of its young pound,” says fish physiologist has dropped by perhaps as Alan Kolok of the University much as 99% in 20 years, and of Nebraska Omaha. These the conservation group Incompounds typically have difternational Union for Conferent effects at high and low servation of Nature (IUCN) doses, he adds. In this case, classifies the eel as critically follicle stimulation occurs at endangered. Now, another low cadmium levels, wherepotential threat to some Euas toxicity occurs at higher ropean eel populations has doses. Kolok has found reproEuropean eels are caught and then grown in fish farms for sushi and other foods, but they don’t reproemerged, according to reductive effects of cadmium in duce in captivity. Researchers estimate they could search published in ES&T (pp fathead minnows as well but be extinct in a decade. 4607–4612). Researchers in says this is the first study he France report that cadmium, has seen that demonstrates a widespread metal contaminant team captured female eels in the that internal stores of cadmium in rivers and estuaries, interferes Loire River and exposed half of can be released during fish migrawith the eel’s complex reproducthem to cadmium in the laborations at levels high enough to be tive cycle. Although cadmium is tory. The cadmium levels of eels in toxic. Some migrating birds “keel probably not the main cause of eel the experiment were environmenover and die” after long migrations declines, scientists say that it could tally relevant; for example, eels because of pesticides released durcomplicate efforts to save the speliving in the cadmium-polluted ing flight, he adds, and other micies because toxic pollution takes Gironde estuary in southwestern grating fish, such as salmon, might years to clean up. France have been found with even be affected similarly. European eels have a notorihigher concentrations of the metal Baudrimont notes that cadmiously complex life cycle that puts in their tissues. Next, researchers um is a contributor to but certainly them at special risk from pollution. injected the eels with hormones not the sole cause of worldwide eel Larvae transform into transparent that stimulate reproductive matudecline, and other experts agree. glass eels and then into yellow eels, ration and placed them in swim The eels won’t spawn in capwhich can live for up to 20 years in tanks, where they swam constantly tivity, making them all the more estuaries. Finally, the eels turn silfor several months to simulate natdifficult to save. Guido van den ver and head for the Sargasso Sea ural migration. Thillart, a fish physiologist at Lei in the middle of the North Atlantic Initially, female eels that had den University (The Netherlands), Ocean to spawn. They swim for up been exposed to cadmium showed is working on hormone-producing to 6 months straight—6000 kilofaster follicle development in their implants that would help eels mameters—without eating. Before the ovaries compared with eels not exture in the laboratory. “If we can journey, they store large amounts posed to cadmium. But as the fish reproduce eels in a regular way, we of fat, and with it, fat-soluble polswam during the simulated migracan see what the effects of cadmilutants such as dioxins and PCBs, tion, the developing eggs of cadmium and other contaminants are in as well as cadmium. um-exposed eels died (in a process the total reproduction of the aniThe eels spawn just once and called atresia), and many of the mal and their population,” he says. then die. The process is so crypeels died as well. —ERIKA ENGELHAUPT June 15, 2008 / Environmental Science & Technology ■ 4239
