Humans building a booster for eels

Water slide is new route over Shore dam


MILLINGTON -- As a sheet of greenish water slipped over a dam, Steve Minkkinen squatted on the wet rocks near the bottom, wielding a power drill and a plastic tube.

He was building a water slide, but not for humans. It's for American eels - a slime-slicked, pop-eyed species that boasts one of the most remarkable life cycles in the animal kingdom.

Because eel populations have been dwindling in the Chesapeake Bay and elsewhere, the federal government is considering endangered species protections, which would prohibit fishing for them. Minkkinen, a biologist with the U.S. Fish and Wildlife Service, is doing his part to try to save the animals by building "eelways" to help them get past dams on their long journey upstream.

Yesterday, he installed a pipe-like passageway over the 10-foot-tall dam built more than a century ago to create Unicorn Lake on a tributary to the Chester River near this Eastern Shore town.

"This will be the first eelway in Maryland," Minkkinen said, plugging in a pump that trickles water down the tube. "It's experimental, but if it works, we hope to build more."

Similarly modified pipes are helping eels migrate past dams in West Virginia, Connecticut and Maine, among other states.

But eels still face many obstacles as they try to swim upstream from the Atlantic Ocean, where they hatch, to the streams and ponds where they spend most of their lives.

Maryland alone has about 700 dams. About 75,000 block about 600,000 miles of rivers across the U.S., including the 17 miles of the Unicorn Branch upstream from this dam.

Several fish passageways - 16 in Maryland - have been built over dams. These include the elevator that lifts shad over the Conowingo Dam on the Susquehanna River. But eels - especially toothpick-sized baby eels, called elvers - can't use these fish devices because the flow of water through them is too powerful, Minkkinen said.

Eelways are more gentle, and they're custom-built for snake-like slithering. The passage over the Unicorn Lake dam is a black plastic tube 18 inches wide and 50 feet long. It has plastic webbing inside, over which a constant flow of 1,200 gallons of water per hour gurgles from an electric pump at the top of the dam.

Instead of slipping down the water slides, the eels wriggle up them. They climb from the pool at the bottom of the dam up and over the top, where they find freedom in the river beyond.

"The eel is an animal that does everything backward, so we had to develop technologies to adapt to it," Minkkinen said, as he demonstrated with his hand how a baby eel would slither up the tube against the current.

In many ways, Anguilla rostrada is the most backward fish in America.

Many species, such as shad, hatch in streams before migrating downriver to the Atlantic Ocean to live most their lives. They return to fresh water only to spawn and die.

Eels are contrarian and slightly mysterious. They spawn amid vast floating mats of seaweed in the Sargasso Sea, a section of the Atlantic Ocean notorious as a graveyard for ships.

After hatching, they morph from larvae into flat creatures shaped like long, skinny leaves. Then they turn into transparent swimmers, called glass eels, Minkkinen said.

Almost invisible, they make their way into the Chesapeake Bay and other inlets. At this point they're called elvers and have an olive-brown hue. They swim up rivers and streams to ponds and swamps, where they live most of their lives in fresh water, gobbling bugs and fish.

After 15 to 20 years, the eels grow to two to three feet long, adopt a yellowish tinge and become sexually mature. When it's time to mate, they switch colors again, this time to silver. Their eyes bulge and their digestive tracts stop working. Without eating, they swim thousands of miles, back to the Sargasso Sea, where they pump out millions of eggs and perish.

"The life cycle of the American eel is probably the most unique life cycle of any species on Earth, with the geographic range and varieties of habitat," said biologist Keith Whiteford, one of three scientists with the Maryland Department of Natural Resources who are helping to build the Unicorn Lake eelway.

Besides blocking the migration of eels upstream - which usually happens at night in June - dams also alter the animals' sexuality, Whiteford said.

When young elvers swim upstream, they're sexually undifferentiated. But too much banging together in fin-to-fin traffic jams at the base of dams can turn the eels into males, Whiteford said.

Scientists don't know why this crowded, locker-room-like milieu produces males. But the pileups clearly hurt reproduction because there are fewer females to lay eggs, Whiteford said.

Eel populations have plummeted over the past 20 years. Besides dams, scientists also point to the harvesting of eels for restaurants in Europe and Asia, pollution and changing ocean currents as possible causes of the decline.

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