updated 12/11/2007 9:50:50 PM ET 2007-12-12T02:50:50

Scientists are trying to determine what caused Lake Champlain's populations of American eels to decline to almost nothing over the last two decades.

And biologists and fisheries experts from Vermont and Quebec are trying to come up with a plan to bring back the population of the snakelike fish, which until the early 1980s were so abundant commercial anglers would harvest tons of them every year.

"We have a fairly large vertebrate that has gone from abundant to virtually absent in 20 years," said Tom Berry, Lake Champlain program director for the Nature Conservancy. "I can't think of another animal whose numbers have dropped so dramatically in the Champlain Valley."

Up until the 1980s commercial fishermen in Quebec pulled tons of eels from the Richelieu River to sell them as delicacies. But by the early 1990s Quebec banned the commercial fishing of eels.

American eels start life in the Sargasso Sea, an area in the Atlantic Ocean between the West Indies and the Azores.

After hatching, eel larvae float on ocean currents to East Coast rivers, including the St. Lawrence. Historically, immature female eels swam up the St. Lawrence and Richelieu rivers and lived 10 to 20 years in Lake Champlain before returning to the Sargasso Sea.

"It is just remarkable they travel 3,000 miles when they are only an inch long. It boggles the mind," said UVM fisheries biologist Ellen Marsden.

Pollution among theories for decline
Biologists do not fully understand the reason for the decline. Theories include climate change, pollution, and overfishing of young eels.

But the decline could also be due to the reconstruction in the 1960s of two hydroelectric dams on the Richelieu River in Quebec. The dams could have prevented the eels from reaching Lake Champlain.

A decade ago, Hydro-Quebec installed an eel ladder at one of the dams. "Within 10 days we measured eels going up the ladder," said Quebec fisheries biologist Pierre Dumont. In 2001 a second ladder was placed on the other dam.

Between 2005 and 2007 Quebec stocked hundreds of eels in the Richelieu. Stocked eels have been found in Lake Champlain. Now it remains to be seen if they come back.

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