One of nature's premier survivors is facing its sternest test yet: Hammered by an array of threats that includes overfishing, pollution, and climate change, populations of freshwater eels, also known as river eels, have fallen to catastrophic lows.
Eels are renowned for their endurance. Atlantic fry drift thousands of kilometers across the ocean to estuaries and rivers, where they can live to the ripe old age of 50 years or more. But the latest data suggest that European fry have plummeted as much as 99% since 1980, and their Asian cousins have declined about 90%. North American eels are suffering steep drop-offs as well. The alarming trend shocked researchers at a meeting last week in Tallinn, Estonia, of the International Council for the Exploration of the Sea, a Copenhagen-based body that advises the European Union on fish stocks in the North Atlantic.
The eel's complex life cycle makes it all the more difficult to determine the reasons for the declining numbers. The transparent, leaf-shaped larvae, or leptocephali, look so different from adults that it wasn't until the turn of the 20th century that they were identified as baby eels. These minuscule critters have countless predators, but they may also be falling prey to alterations in the Gulf Stream, which normally sweeps the leptocephali to Europe and North America. Even subtle shifts in the Gulf Stream, linked to cyclical phenomena such as changes in winds around the North Atlantic, may condemn many to death in the Arctic, for example.
Those lucky leptocephali that reach estuaries and rivers transform into elvers, or glass eels. These transparent juveniles are netted by the millions primarily because they can be raised in farms to satisfy massive consumer demand in Japan, where grilled unagi is a favorite dish. Glass eels are also likely to be falling victim to organic pollutants and dams that pinch off upstream habitat, researchers surmise.
Scientists are hoping to persuade governments to step in and regulate eel fishing. "It's an absolutely uncontrolled industry" in Europe, says Willem Dekker of the Netherlands Institute for Fisheries Research in Ijmuiden. The European Commission today released a recovery plan that calls for careful management of eel catches at all stages of the life cycle. Scientists are lobbying for similar measures in Japan. Unless strong action is taken soon, warns Dekker, "the future for the eels will be bleak."