Maryland Dams Get New Pathways for Eels

By Linda Orlando

The American eel is found all along the Atlantic coast, but is most abundant in the Chesapeake River and its tributaries. For centuries the eels have made their way upstream as juveniles, heading from the ocean inland to spend the rest of their lives in freshwater tributaries. But when Maryland biologists discovered that the eel population was in decline, they set about trying to find out why.

Although there are about 50 watermen in Maryland who still make a living off catching eels and selling them abroad to restaurants, the decline in numbers of eels isn’t entirely due to fishing. Biologists studying the problem believe that one of the primary causes of the population decline is the numerous dams along the waterways that eels travel. American eels are crafty fish that can slither around rocks and branches with just a small amount of water. But eels aren’t very strong swimmers, so when dams block their natural migration patterns, they can’t make their way upstream and they die. The dams throughout the Chesapeake Bay watershed, in particular, may be causing the problem in Maryland.

Maryland has over 1,000 dams, but only 16 of them have been modified to allow fish to pass through so they can head upriver to spawn. However, biologists in recent years have determined that the modifications made to allow herring and shad to pass through dams doesn’t work for eels. Because eels are only about 4 inches long when swimming upstream, not many of them can power their way through traditional fish passages. Eels prefer slower-moving water than river currents, migrating at night along the banks. "They can’t swim in really heavy currents," said Steve Minkkinen, a biologist with the U.S. Fish & Wildlife Service Maryland Fishery office. "They’re looking for slow water."

To work toward a solution that will give the eels a boost, Minkkinen and four other state biologists built a passageway for eels on a 10-foot high dam at Unicorn Lake in Queen Anne’s County. Although eelways are common across New England, the Unicorn Lake eelway is the first in Maryland. Ten more are planned for other locations.

Minkkinen’s eelway is a pretty simple concept; it began with a length of black plastic pipe such as the ones often place beneath roadways. Plastic netting was glued to the bottom inside the pipe, because eels need something to crawl on for traction. A trickle of water was pumped down it to keep the netting wet, but not moving fast enough to make it difficult for the juvenile eels to pass through the pipe. The plastic tube was placed on top of an existing fish chute, and the top was angled down to dump into the lake on the other side.

No one knows how far down the population of the American eel has dropped, but the national eel harvest was less than a million pounds last year. In the mid-1970s, about 3.5 million eels were caught each year. The U.S. Fish & Wildlife Service is deciding whether or not to name the American eel an endangered species. The Atlantic States Marine Fisheries Commission estimates that 84% of upstream habitat has become unreachable for eels, partly because of the impassable dams. "We know over time that dams have decreased the number of eels," said Steve Gephardt, an eel expert at the Connecticut Department of Environmental Protection. "They can wiggle around a lot of stuff. They can do a lot of tricks, but in fact they don't swim that well. So you have to think like an eel, and the fishways we were building weren't doing that."

Minkkinen hopes that the low-tech eelways—which cost only about $2,000 for small dams—will begin to turn around the population. Most people don’t care for eels because of their snakelike appearance, but eels are important food sources for other fish and birds of prey. They also play an important role in mussel reproduction, because mussel larvae attach to eels. In rivers that no longer have eels, the mussels have also disappeared.

"It's a species that hasn't been considered much, unfortunately," Minkkinen said. "But they're important ecologically. Right now eels can't get into a lot of their habitat, so let's open up as much habitat to them as possible."