The Lowliest Fish in the Bay
Conowingo eels might just be one of the most important species in our waters
The only eel I have seen in the last 20 years was on sushi.
That changed in a big way as I gazed at a tank teeming with the wriggling creatures.
“We call them pencil eels; they’re about four inches long,” said my guide, Ian Park of the U.S. Fish and Wildlife Service. At the base of the Conowingo dam on the Susquehanna River, we were tending to an experiment that could unlock a key to restoring Bay water quality. Park’s job was to move the eels from a collection tank to a holding tank.
Today’s take was about 5,000 eels, not bad for the three days since the last collection. There were now over 8,000 critters in the holding tank. In a few days, Park would use a tanker truck to take these eels upriver to the heart of Pennsylvania for release.
The American eel is hardly a popular fish in the Bay. It is no longer an important commercial catch; not a popular menu item; and not part of our recreational fishery. Add the snake-like appearance that many people find repulsive, and you have the makings of a species most people care little about.
Maybe We Should Care
The scientists at the U.S. Fish and Wildlife Service have a different view. They think the eel might be an important piece in the Bay restoration puzzle and are working the science to prove it.
The eel itself doesn’t do much to help the water quality of the Bay, but there’s another critter — the freshwater mussel (Eastern elliptio) — that filters water the same way that oysters do. In the Delaware River, an estimated 280 million mussels filter four billion gallons of water a day and remove 78 tons of sediment from the water.
What’s the connection between the mussel and eels?
The mussel larvae must attach to a host fish to mature; their favorite host is the American eel.
The Susquehanna River used to teem with these mussels, but no longer. The river supplies 43 percent of the Bay’s water; no mussels there mean dirtier water flowing into the Bay. Fish and Wildlife scientists believe the mussel population has declined because the eel population in the Susquehanna has dropped to almost zero. No eels means no host for the mussel larvae. No host for the larvae means no mature mussels to filter the water.
The disappearance of the eels is no mystery. In the early 1920s, a series of four dams was built across the river. A growing nation needed electric power, and the dams seemed an economical way to generate it. The best known of these dams is the one closest to the Bay: the Conowingo.
Over the years, the effect of the dams on the shad and herring populations were recognized. Lifts and ladders were constructed to allow these fish to migrate upriver. Baby eels must migrate upriver too, but the shad lifts won’t work for them. Eels were not considered an important species, and no accommodations were provided. As a result, the eel population upriver of the dams decreased … mussels decreased … dirtier water flows into the Bay.
In theory, the solution is simple: Get more eels upstream and you will have more mussels; more mussels mean cleaner Bay water. But both eels and the mussels are slow growing, so it’s taking a while to prove the connection.
So for five years, Fish and Wildlife has been collecting eels at the bottom of the Conowingo dam and trucking them upstream past the fourth dam, then releasing them. Over 300,000 eels have been captured and released. This year, year five of the experiment, is when scientists start looking for increases in the mussel population.
A Different Kind of Fish
In the meantime, Fish and Wildlife scientists have learned a lot about eels. Eels have an unusual life cycle, spending most of their lives in fresh water. When they mature, they head downstream; usually there is no problem getting through the dams in that direction. To breed, they swim far into the Atlantic Ocean to an area known as the Sargasso Sea. The hatchings then head back toward fresh water.
At the end of their first year, they are at the entrance of the Bay; it takes another year to make it up to the Susquehanna River. Then they hit the dam, and the journey ends. This is where science intervenes.
The collection system looks like it was cobbled together with spare parts out of the service’s basement, which it was. It works because of the nature of the baby eels to swim — or wriggle — upstream. The collection chute resembles a miniature water slide used in reverse. Eels climb up the slide and drop into the collection tank. From there, the science taxi trucks them upriver so their normal life cycle can continue.
Exelon Generation, the owner of Conowingo and Muddy Run, is supportive, providing space for the collection system and pumping the river water to make the system work and keep the eels in the holding tanks healthy.
“This is an important project for the environment,” Robert Judge, Exelon regional communications manager, tells me. “Exelon feels partnership with the U.S. Fish and Wildlife Service will help restore the eel population on the Susquehanna.”
Exelon has also provided a $20,000 grant to further the work. This year, as Exelon’s license for the power station comes up for renewal, eels are expected to be part of that discussion.
Like all the efforts to restore the Bay, this one will take years to produce results. It’s even possible it will never yield a benefit. On the other hand, it isn’t costing us a lot of money, and it looks promising.
My next visit to my favorite sushi restaurant, I’ll be looking at the unagi — that’s eel — in a new way.