Great Lakes eels are a conservation challenge

Image: Ellen Edmonson and Hugh Chrisp.

Something slithers beneath the surface of the Great Lakes and it’s not a sea lamprey.

It might look similar, but the mysterious American eel isn’t a sucker. And it’s in trouble. Its population is decreasing dramatically and no one is sure why.

The fish is native to Lake Ontario, but man-made locks and canals expanded its range to the other lakes, said Steve Patch, a fish and wildlife biologist with the U.S. Fish and Wildlife Service.

It’s also in inland water ways of Illinois, Indiana, Michigan, New York, Ohio, Pennsylvania and Wisconsin.

As adults, the fish are slimy, scaleless, have yellow and brown bodies and long dorsal and anal fins.

“They might be slimy, but they are slimy and mysterious,” said Kate Taylor, the American Eel Fisheries Management Plan Coordinator for the Atlantic States Marine Fisheries Commission.

A mysterious life cycle

The fish lives most of its life in freshwater.

Opportunistic feeders, it eats frogs, crayfish, insects, snails, earthworms, larval lamprey and fish like the invasive round goby.

The eels then migrate to the Sargasso Sea – a section of the Atlantic Ocean near Bermuda where all American eels spawn. That’s more than 1500 miles from the mouth of the St. Lawrence River through which all Lake Ontario eels must pass.

Young transparent eels, known as glass eels, then make their way back to rivers and streams along the Atlantic coast, including the St. Lawrence River.

Unlike other migratory fish, they don’t have a homing signal, Taylor said. They come back to rivers and streams, where they mature, at random.

But the number of eels returning to Lake Ontario and the St. Lawrence River has declined drastically.

A sharp decline

In the 1980s, more than a million eels a year climbed the eel ladder on the Canadian side of Moses-Saunders dam on the St. Lawrence River, Patch said.

Last year there were about 40,000 – at least a 96 percent decrease.

The decline was significant enough to close a once-prominent Ontario commercial eel fishing industry in 2004.

“During the 80s and 90s, it was one of the top three species of economic value in terms of Lake Ontario and St. Lawrence River fisheries,” said Alastair Mathers, a fisheries biologist at the Ontario Ministry of Natural Resources.

But the catch numbers declined in the St. Lawrence River near Cornwall about 99 percent between the early 1980s and 2002.

The reason is unclear.

There are many possible reasons for their decline and no one knows which one it is, if it’s a combination or if they’re all contributing, Patch said.

Possible reasons: Habitat loss, dams that impede migration, changes in ocean currents, contaminants and seaweed harvesting in the Sargasso Sea.

Difficult to conserve

Lack of answers combined with its unique life cycle make conserving the eel particularly difficult.

Conservation to help a population may not lead to an increase in that river, state or even that country since young eels migrate to rivers randomly, Taylor said.

Because they range from Greenland to South America, conservation must span national and international governments with unique regulations.

“As the eels are out migrating, going to their spawning ground, they’re crossing the state waters then federal water and then eventually out to high seas waters,” Taylor said.

An unclear future

In 2007 the U.S. Fish and Wildlife debated whether to list freshwater eels as an endangered species.

Despite the sharp declines in some areas, the agency declined to list it because other areas showed population increases.

“We reviewed it and determined that it was not worthy of being designated,” Patch said. “It wasn’t clear what was happening whether it was increasing or decreasing in various places.”

A new review is underway and the agency decision is expected to decide whether to list them as endangered in the next few months, he said.


In 2008, Ontario listed the eel as a species at risk.

The law prohibits killing endangered species without permission,and officials are working with hydroelectric companies to reduce the mortalities of eel migrating to sea to spawn. In 2006 Ontario Power Generation, which operates half the dams on the St. Lawrence River, implemented a $2.5 million 5-year plan.

It includes using specifically designed ladders that eels can use on the way up stream. But on the way down adult eels are forced to navigate dam turbines.

“It’s thought that about 20 to 25 percent of those migrating towards the spawning ground would be killed by the blades,” Mathers said.

Adult females grow up to five feet long and males measure up to just a foot and a half.

To help in their downstream migration, the power company is stocking eels from Maritime Provinces and monitoring the program’s effectiveness. Eels are also trapped upstream of the dam and transported beyond it while the company explores new options.

How effective these measures are is unclear.

“We are continuing to learn about the effectiveness of stocking as well as the trap and transport projects,” Mathers wrote in an email. “There is no way to directly keep eels from passing through the turbines at this point in time and we need to keep working on this problem.”

© 2011, Great Lakes Echo, Michigan State University Knight Center for Environmental Journalism.

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