While the first reaction to seeing the creature might result in a cringe or cry for help, their predecessors were here long before the modern-day anglers who now fish the river.
The American Eel (Anguilla rostrate) is a natural part of the river ecosystem, and has been impacted by the four hydro-electric dams placed on the Susquehanna River.
American eels are one of the few catadromous species in world, which means that the adults swim out of freshwater tributaries and into the sea to spawn, the opposite of salmon.
The young eels — called glass eels — drift with ocean currents until they find their home tributaries. As they grow, in their next stage they are called elvers, and it is in this stage that they ascend the rivers and tributaries where their parents matured.
The eels grow to maturity — for about 10 to 14 years — in their native rivers, at which point they descend downstream to the ocean to spawn in the Sargasso Sea. The dams hinder both the upstream migration of the elvers and downstream migrations of the adult eels.
The United States Fish and Wildlife Service (USFWS) is currently involved with restocking eels, studying their movements, and working on helping the eels navigate around dams.
Eel harvest was once an important part of the local river economy. Eel “weirs,” V shaped formations of rocks used by eel fishermen in the early 1900s, are still very visible during low water periods in the river.
During darkness, eels migrate downriver, and the eel fishermen tending their weirs would place a basket at the bottom of the “V.” If far from shore, they would spend the night in a houseboat, waking every several hours to empty the eel basket into holding barrels on the boat. At daybreak, the baskets would be removed from the weirs and the boat would come to shore with their catch. Some would be put in holding tanks and kept alive for later sale, some would be pickled, and some would be sold fresh to local buyers. Many local eel weir operators made a substantial part of their income from the eel run.
The building of the Conowingo Dam in the early 1900s, followed by the Holtwood Dam, Safe Harbor Dam and York Haven Dam in the following years severely impacted the eel migration and eventually the population.
Some eels did survive however, and part of the licensing agreement with the companies that owned the dams was a requirement to transport eels around the dams. That licensing requirement ended and by the 1980s eels were becoming rare and were largely gone by the 1990s.
Why eels? Eels are part of the freshwater mussels’ life cycle. Freshwater mussels are the natural filters in our streams and rivers. They pump water and filter out particles, some of which they consume.
When freshwater mussels are born, they lack the ability to pump or filter water on their own. The new born mussels, called glochidia, attach to the gills of eels and are carried for about two weeks, using the movement of water through the gills to help them feed. They then drop off and continue on their life cycle, able to then pump water on their own. According to a report from the Natural Resources Conservation Service, some fresh water mussels can filter up to 10 gallons of water a day.
According to Joshua Newhard, fisheries biologist with the Maryland Office of the USFWS, eel stocking (moving elvers upstream from dams) started in 2008 and has continued yearly since then, with over one million eels stocked.
Eels are doing well according to Newhard, and have spread thoughout the river and many of its tributaries. With eels doing well and growing steadily, the next step, according to Newhard, is to study the outgoing migration and looks for ways to improve survival of eels passing downstream through dams.
Between 2012 and 2018, Newhard’s team tagged 1,755 eels with PIT tags, tiny transponders that allow biologists to identify each individual eel location and movements. The PIT tags are tiny transmitters about the size of a grain of rice that are implanted just behind the head.
In a summary published by Newhard in 2018, he reported some interesting statistics: 196 eels were recaptured three times, two eels were recaptured four times, and one was captured five out of seven years. Yearly growth rates for eels ranged from 3/4 of an inch, to about 4.6 inches, and averaged 1.83 inches.
With the USFWS fisheries biologists on the case, it appears the eel restoration is in good hands and doing well.
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