The Gulf Stream carries the tiny larvae back to Europe where they grow into transparent juveniles known as glass eels. The juveniles run up rivers, spending anywhere from two to 80 years in freshwater before their migratory urge calls them back to the ocean.
The migratory instinct is so strong that some adults will writhe overland for up to 24 hours between landlocked ponds and sea-bound rivers to reach the ocean.
One theory why eel offspring return in smaller numbers is that the system that delivers them is failing. Scientists speculate that warmer waters due to climate change are altering Atlantic currents, including weakening the Gulf Stream that runs north towards Europe and plays a vital role in transporting eel larvae.
Dekker, the Dutch biologist, said: "My own recruitment sampling of juveniles here in the harbor at Ijmuiden once produced the highest catch ever observed, but this year yielded zero recruits."
Moreover, Eels that do succeed in reaching freshwater habitats in Europe face the prospect of capture, not only as food but as wild seed supplied to fish farms in Europe and the Far East. (Eel have yet to be bred successfully in captivity.)
In the early 1990s Europe's estimated glass eel catch totaled 1.5 billion fish.
Adults are also trapped in rivers at the start of their long migration5,000 metric tons of them each year across Europe. In North America, American eels have been subject to similar pressures. Numbers in the Great Lakes collapsed five years ago, almost wiping out a long-established commercial fishery.
"There's an astonishing parallel in the time trends of both Atlantic species," Dekker said. "This has been interpreted as evidence for a common cause [for their decline]."
As well as overfishing and ocean warming, other perceived threats include dams, which block migration, harmful parasites introduced via aquaculture from the Far East, and contamination through pesticides and the toxic industrial compound polychlorinated biphenyl, or PCBs.
Whatever the cause of the eel's decline may be, one thing is clear: The effect for those who depend on eels for their livelihood could be catastrophic. Eel fishing and aquaculture are major sources of employment. Europe, for example, has an estimated 25,000 eel fishersmore fishers than for any other species.
But as Dekker points out, both fishermen and eel stocks are spread widely across the countries of Europe and other continents, making the task of coordinating and monitoring conservation efforts extremely difficult.
He said: "The eel population is distributed all over Europe, north Africa, and Mediterranean Asia. That is a wide area, but nowhere can one find a large-scale fishery. Typical situations comprise one or two fishermen, using small boats, catching one to two [metric tons] per man per year. This has been a major obstacle for us in collecting information on the eel's status, in attracting political attention, and will hamper implementation of protection measures."
Despite such difficulties, the European Commission now hopes to have a long-term management plan in place by the end of next year. It will target all stages of the eel's life cycle. For instance, limits will be set on fishing for glass eels used in aquaculture, while eel passes, similar to salmon ladders, are to be introduced to lessen the impact of dams and weirs that block upstream migration.
Experts say the effectiveness of such measures could prove crucial not only in deciding the eel's future, but the fate of those who still rely on the fish returning from the Sargasso Sea.
SOURCES AND RELATED WEB SITES