Delaware Center for the Inland Bays

By Zachary Garmoe, Science Technician at the Center for the Inland Bays

Andrew McGowan, the Center’s Environmental Scientist, and I crouched on a slip of land nestled between a pond and a roadway one chilly February morning, our backs feeling the cold breeze made by cars rushing by on their way to work or school or some other destination. While I was well aware of our purpose for being there, the site itself appeared decidedly unremarkable.

But the site is actually quite remarkable, as it is a vital point along a treacherous migration route for an important local species. On that February morning, Andrew and I met at an undisclosed location in the Inland Bays to set up a passageway for juvenile eels, known as elvers, to cross over a small dam. Without the Center’s help, the young eels would be unable to continue upstream and reach their ideal habitat after their lengthy journey from the Sargasso Sea, an area roughly between Bermuda and the Caribbean.

The American eels traveling through this passageway are young, but have already journeyed hundreds, if not thousands, of miles to reach the Inland Bays. American eels are catadromous, meaning they live in brackish and freshwater, but spawn in the salty ocean. Born in the Sargasso Sea, juvenile eels will drift in the open ocean, sometimes for more than a year or so, until currents carry them toward land, where they then begin to travel up the nearest river or estuary. 

Even though they’re called the American eel, their range is far greater than just the northern continent. This species is found

as far north as Greenland and as far south as Panama. Once they reach a suitable home site, they will spend the next 10-30 years living out the majority of their adult lives by feeding on mollusks, crustaceans, and small fish.

Another fun fact about eels: they have the ability to absorb oxygen through gills as well as their skin, meaning they have the ability to travel over land for short periods of time!

If they survive the various pressures set forth by humans and other predators, they will eventually begin to once again move downstream toward the open ocean. No one knows exactly what initiates their return trip and when, but during their return to the ocean, they will turn silver, stop eating, and their digestive system will disintegrate. When they finally reach the Sargasso Sea, the eels will spawn and the cycle begins once again. It is assumed that after spawning, the eels die in the Sargasso Sea, but to date, no scientists have ever actually observed this phenomenon. 

Eels face a large number of pressures here in the Inland Bays, both natural and otherwise. A number of other fish and bird species, such as herons and striped bass, will prey on American eels. Additionally, eels have historically been used as fishing bait, and can be caught recreationally in Delaware if they are over 9 inches. However, juvenile glass eels can fetch a very high price for sushi and can become the victims of poaching. 

Then there are dams, like the one Andrew and I were working to bypass, that can block eels from reaching their ideal habitats. Remarkably, the Delaware River to our north makes for some of the most ideal eel habitat because there is not a single dam along its 330-mile main stem. 

While the same cannot be said for some of the creeks and tributaries in the Inland Bays, there are still ways we can help and protect our eel population. By installing these temporary eel passageways, or eelways, we help eels successfully migrate upstream and reach habitat that would otherwise be inaccessible to them. This is particularly important because unlike other migratory fish species, eels don’t return to the waterways previously inhabited by their parents. The eels traveling upstream this year may be the offspring of eels from Florida or from Nova Scotia or from nearly anywhere along the coast of North America. 

Conservation of eels anywhere helps eels everywhere. 

And it truly is a remarkably beautiful sight to see: thousands of nearly crystal-clear eels, slowly marching their way upstream to live their lives in the upper reaches of the Inland Bays watershed.

So, the next time you pass over a bridge in February and March, think of the eels slowly traveling beneath you, continuing their long journey toward their homes in our beautiful Inland Bays. 

To learn more about migratory eels in the Inland Bays, visit our website at inlandbays.org/inland-bays-migratory-fish-passage.

And if you really want to dive into the wonderful world of American eels, check out these additional resources:

• American Eel fact sheet (U.S. Fish & Wildlife Service)
• Eels and Mussels—An Unlikely Pair
• Map of the continental range of the American Eel 
• For the Endangered American Eel, a Long, Slippery Road to Recovery