Where do eels originate?

The American Eel (Anguilla rostrata) has interested me since I was a youngster. It started young in my family’s cottage. We were night fishing for bullhead catfish in a little creek when I hooked onto something too big to be a bullhead. By the time I got the fish to shore, we realized it was an American eel. 

 

 

My family had fished this stream for years, unaware of the presence of such a massive, strange beast. I recall being amazed by a fish that was unlike the bass and pickerel I was used to catching. We didn’t know what it was and swiftly let it go to escape its teeth and slime-covered body. 

 

 

This unexpected meeting inspired me to learn more about the eel’s life cycle and environment. To my surprise, my tiny stream (and the eels that live there) are part of a much bigger global ecology.

 

 

The life cycle of freshwater eels has long been unknown. For decades, European philosophers and scientists couldn’t explain why eels lived in freshwater. Many European streams have eels, including ephemeral (temporary) waters and impoundments. 

 

 

But these eels never spawned, and ‘closer investigation’ revealed no reproductive structures. Others have produced fascinating hypotheses on how eels breed, including Aristotle and Sigmund Freud. 

 

 

How were these freshwater eels reproducing and where did they originate from? Die Antwort ist viel komplexer als die früheren Forscher wahrscheinlich erkannt have

 

We now know that all European (Anguilla anguilla) and American (Anguilla rostrata) eels originate in the Sargasso Sea in the northwest Atlantic Ocean. 

Schmidt began searching the ocean for young eels in the early 1900s, recording the whereabouts of smaller and smaller larvae for over two decades before tracing them back to the Sargasso Sea. 

 

 

The Sargasso ‘Sea’ is an Atlantic area without land borders. It is surrounded by a ‘gyre’ of ocean currents. Gyres are circular ocean currents affected by wind and earth rotation. The term ‘Sargasso’ comes from early explorers describing the brown Sargassum seaweed abundant across the area.

 

 

Adult American (and European) eels spawn in the Sargasso Sea. Eels are catadromous fish, meaning they spend their adult lives in freshwater before returning to the sea to spawn. The eels then begin a life cycle that comprises many physical metamorphoses and a 4,000-mile round-trip migration. 

 

 

Eels hatch in the Sargasso as tiny, translucent larvae. That’s called Leptocephalus (slim-headed) in young sea eels. The larvae then travel along the ocean currents to freshwater habitats. (American and European eels both hatch in the Sargasso Sea, but how their larvae know which direction to migrate is unknown.) As eels approach their target, they transform into ‘glass eels.’ But the eels are still translucent. Their coloration gives them the name ‘elvers.’ 

 

 

The eels then migrate into freshwater environments along the coast, reverting to their classic yellow eel shape. Their bodies become serpentine and muscular. A residence may be hundreds or thousands of kilometres upstream. 

 

 

During this voyage, eels may go across land and stay in arid ecosystems for long periods of time. This talent guided the eels I captured at my family’s cabin. They could get across a massive cascade that separates my creek from a larger river downstream.

 

 

 

Adult eels are freshwater predators that feed at night on a variety of food (in my experience, it was a dead minnow on a hook). Eels may survive for fifty years or more in their freshwater habitats before migrating back downstream to their birthplace in the Sargasso Sea. (What makes them proliferate is yet unknown.) 

 

 

The eel’s body changes again, becoming more marine-friendly. Finally, eels have reproductive structures (which explains why early European scientists were unable to observe them). Silver eels are the last reproductive phase of eels. The eels spawn and die in the Sargasso Sea, ending a long and strange voyage.

 

 

 

Status of refor

American eels are threatened throughout the Chesapeake Bay watershed and beyond. Global eel catch has decreased since the 1970s, indicating population collapse. 

 

The reasons for this include man-made issues like invasive species and commercial harvesting. Dams have obstructed eels’ migration between freshwater habitats and their breeding sites in the Sargasso Sea, affecting reproduction. American eels may be threatened by invasive species like flathead catfish (recently introduced into the Chesapeake Bay Watershed). 

 

 

Migratory and reproductive patterns may be affected by climate change. Pollutants and wastewater entering freshwater systems through runoff harm adult eel habitat. The Sargasso Sea has microplastics, garbage, and macroplastics in their breeding habitats (see North Atlantic Garbage Patch).

 

 The International Union for Conservation of Nature (IUCN) has designated the American eel as ‘Endangered’ owing to declining population trends and reduction of mature individuals.

 

 

Chesapeake Bay Eels

The American eel was formerly widespread in the Chesapeake Bay Watershed. Eels would have readily migrated between their Sargasso Sea origin and the various freshwater streams across the bay watershed. 

 

Native Americans used weirs in freshwater rivers to catch migratory eels. Their stone weirs may still be seen today. It is called from a Susquehannock phrase meaning ‘the spot where we eat eels’. 

 

After European colonization, commercial eel fishing grew in several locations, capturing millions of pounds annually. Dams were built on numerous river systems within the bay watershed, blocking eel migratory paths. Many of these water systems still include eels, although their populations have declined owing to commercial fishing and dams. 

 

Fish passageways are presently being installed to reestablish these migratory pathways. American, European, and Japanese eels are still utilized in traditional sushi recipes. Anglers in the Chesapeake utilize American eels as bait, particularly for stripers (or rockfish if you are south of Pennsylvania).

 

 

The Alliance’s PA office and Lancaster County Conservation District collect data on electrofishing specimens for monitoring. Below the Conowingo Dam, on Octoraro Creek, an American eel was caught (Photo by Jenna Mackley).

 

 

A Novel Relationship

Elliptio complanata is a widespread freshwater mussel in the Chesapeake Bay Watershed. Mussels are filter feeders and are bivalve mollusks. The mussel feeds by siphoning organic particles from the water using its gills. Mussels like clear, cold, nutrient-free waters with little sedimentation. 

 

 

Eels need clean freshwater environments with plenty of prey, as well as unimpeded migratory routes. Historically, mussels and eels were prevalent in these ecosystems across the bay watershed. But the loss of riparian woodlands reduced water quality and mussels and eels.

 

 The eastern elliptio mussels are submerged in the stream silt, their siphons projecting slightly from the shell. The complicated life cycle of this mussel species and its interaction with the American eel was just recently revealed to me.

 

 

Eastern elliptio mussel tagged in the Cacapon River, WV (Photo by Andy Meyer).

Eastern elliptios are still found in the bay watershed, although were formerly more common. Some Susquehanna River tributaries now lack young eastern elliptios, indicating a reduction in reproductive success. Many folks live to reach 100 years old or more. 

 

 

WHY IS THE JUVENILE MUSSEL DEC In North America, most mussels need fish hosts to reproduce. Eastern elliptios follow suit. Male elliptios discharge sperm into the water, which females then pick up while they drink. The female mussel’s eggs are fertilized and begin to grow. 

 

The glochidia (larvae) of the baby mussels are discharged into the water. The glochidia connect to the host fish’s gills and grow into small mussels. The mussels then disperse from the fish and survive for decades in the stream sediment.

 

 American eels are the principal host of eastern elliptios. While they may reproduce with different fish species, eels have shown to be the most prolific host. 

Because so many dams along the Susquehanna restrict their migratory path, eel populations have dropped in several streams, reducing elliptio reproduction. Biologists and fishery managers have started releasing eels above these dams to slow the loss. 

 

This method, together with the creation of fish tunnels, seems to be helping eel migration and elliptio reproduction.

 

 

 

 

The Chesapeake’s Eel and Mussel Future

Our efforts to restore the Chesapeake Bay Watershed are directly linked to the future of eels and mussels. The Alliance works to repair rivers and promote clean water and healthy ecosystems across the bay watershed. 

 

This is accomplished by reducing sedimentation, trapping nutrients, and filtering runoff via our riparian buffer and reforestation projects. Tree canopies give shade and cold water. 

 

It also helps farmers and producers better manage waste and prevent animals from entering rivers. These methods help eels and mussels thrive in a healthy ecology.

 

 

Historically, every American eel residing in the bay watershed had access to a clean Chesapeake Bay. Despite the dangers, they have optimism for the future. In addition to dam removal/fish passage infrastructure, improved knowledge of their life cycle will only benefit this species’ survival.

 

 

My unexpected meeting with an eel and subsequent comprehension of its complicated life cycle impacted my choice to pursue a career in natural resource management. 

 

As the Alliance’s new Pennsylvania Forest Projects Coordinator, I can help eels, mussels, and other creatures in the bay watershed by promoting and implementing habitat efforts. 

 

Protecting these treasures will allow others to enjoy them like I did as a child, fishing at my family’s cottage and collecting mussels in the stream.