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The American Eel Scientific name: Anguilla rostrata Length: averages 24 - 40 inches Mass: up to 30 pounds Coloring: varies during life cycle; transparent to olive green to yellowish brown to a silvery gray Feeding Habits: differentiates while maturing; plankton, dead fish while young & small crustaceans, frogs and fish when in freshwaters Predators: large aquatic mammals, fish-eating birds and large fish like bass Defenses: body is covered in a slimy substance in hopes to deter predators, and fishermen, from holding on Habitat: catadromous species; lives life in freshwater, but spawns in salt water Importance to Society: elvers & adults are considered delicacies in several countries; overharvesting is a major concern in this market Conservation status: unprotected but carefully monitored due to decreases in populations worldwide. More information on the characteristics of the American eel can be found on the Animal Diversity Web.  Not to be Mistaken with... The American eel has the unfortunate luck of sharing a similar appearance with an Indiana invasive specie – the sea lamprey. You can differentiate the species by taking notice of the dorsal fin. The eel’s is a single, continuous fin staring from the dorsal side to the pelvic area while the sea lamprey’s fin is notched. The invasive also lacks a jaw; a sucker-type moth can be found instead.

The American eel is a fascinating creature with an even more fascinating life history. Found throughout the United States and the Atlantic coast, it is hard to imagine that there is still so much we do not know. Something we do know is that American eels are common in Indiana waterways, and how they get here is nothing short of remarkable.  

The Mysterious American Eel  

The American eel is a species that has intrigued even the greatest thinkers of our time. While adult eels were abundant in numbers along coasts and in freshwater waterways, no one could find the fish in juvenile form nor did they know where the eels spawned. In 4^th century BC, Aristotle recorded the first observation on the life of an eel. He believed that eels were created spontaneously from the mud of river bottoms. Pliny the Elder – an ancient natural philosopher – thought that young eels grew from skin that adult eels had rubbed off against rocks. While both theories seem entirely unbelievable, no one could prove them false until Johannes Schmidt found the eel’s spawning grounds in the Sargasso Sea in 1922.

Since Schmidt’s discovery more information has been discovered about the American eel, but the snakelike fish still eludes scientists in many ways. Although where the eels spawn in well-established, no adult eel has even been found in that area. Spawning behavior and the fate of the adult eels are also a mystery. However, what we do know is that the American eel is an amazing species with keen migratory instincts and physical transformations that help it along its way.  

 

Transformations with each Destination:
The Migration of the American Eel 

The American eel’s migratory instincts are beyond incredible. Beginning its life in the Atlantic Ocean’s Sargasso Sea, the catadromous fish must find its way to freshwater rivers, lakes and estuaries. The range of habitat is expansive; from the southern tip of Greenland, along the Atlantic coast of North America, throughout the Gulf of Mexico and the Caribbean and inland for the St. Lawrence Seaway in New York to the Great Lakes of the Midwest, the eel makes its way there and all the way back to its salty spawning grounds.

 

With each geographical change the American eel makes comes a physical transformation. The larvae, called leptocephalus, are transparent, leaf-shaped and appear nothing like an adult eel. For about a year the leptocephalus drifts along with the Gulf Stream before entering coastal waters. Prior to entering the coast, the eel will make its first transformation into a more eel-like shape, though still transparent, and are called glass eels. As it makes its way into estuaries, the glass eels become longer and pigmented - taking on a brown or grey color - and become elvers.

Elvers will overcome seemingly impassable obstacles to get where they want to go, even if it means leaving the water to travel on land for a short distance, swimming through rapids or up dams. It can take elvers years to reach its destination, traveling for hundreds of miles to do so. When it completes its journey, the elver will make another transformation into a longer, more yellowish creature known as the yellow eel. The yellow eel is evasive and nocturnal, preying on aquatic invertebrates, amphibians and fish.

During the yellow eel stage, the animal will recognizably become a male or female. Usually females are found in freshwater habitats while males are found along the coastal areas. Females will return towards the males once they have sexually matured – which  can take as long as twenty years. This takes place during the final metamorphous when the yellow eels become silver eels. Silver eels are longer, thicker and take on a metallic black-bronze sheen with a pure white belly. Just prior to their return migration, the eel stops feeding and its eyes and pectoral fins enlarge. Silver eels swim towards their salty grounds during their winter months in order for a January spawning in the Sargasso Sea’s warm waters. It has been determined that American eels die after reproducing, but like the many aspects of the eel’s life, this is not for certain.

 

 

On the Decline

Despite the fact that the total population of American eel’s exceeds over a million worldwide, their numbers appear to be on the decline. In December 2004, the U.S. Fish and Wildlife Services was petitioned to consider protecting the American eel under the Endangered Species Act. Many believed that overall population has waned due to barriers to migration routes, habitat loss, hydropower plant mortalities, pollution and overfishing. After a few years of research and debate, the FWS concluded that there was not enough proof indicating that American eels where threatened or endangered of becoming extinct in the near future. According to fishery biologist Heather Bell, fluctuations in American eel populations are common, and the recent decline in numbers don’t indicate an irreversible trend. In January of 2007, the U.S. Fish and Wildlife Services determined that placing the American eel under the protection of the Endangered Species act was not warranted.

Although federal protection has been deemed unnecessary, many states are working to protect the American eel in their waters. Harvest limitations have been implemented as well as projects to remove manmade dams interrupting historic eel migrations routes and building eel ladders at hydropower plants.  While the American eel is biologically and economically important to the states off the Atlantic coast, it’s presence in Indiana is a reminder of how amazing the biodiversity of our planet truly is and how each creature should have the opportunity to strive.

American Eel's in Indiana

Historically, eels were found in Lake Michigan, Lake Erie, Kankakee River and the Ohio River. Today they can also be spotted in both White River and Blue River watersheds. According to NatureServe, recent evidence concludes that eel populations have declined since the 1970’s. However, the information is based on surveys with a very small number of eels, so determining whether the decline is a normal fluctuation or a trend is complicated. While the American eel is economically important to the states off the Atlantic coast, it’s presence in Indiana is a reminder of how amazing the biodiversity of our planet truly is and how each creature should have the opportunity to thrive.

For More Information

U.S. Fish & Wildlife Services - The American Eel 

U.S. Fish & Wildlife Services: Life Histories and Environmental Requirements for the American eel

USGS - Nonindigenous Aquatic Species - Anguilla rostrata  - with an interactive map

The Nature Conservancy's New York Chapter's work with sonar and eels. Check out the slideshow and sonar video of eels swimming.

North American Native Fishes Association's information on American eels

Underwater World of the American Eel from Fisheries and Oceans Canada

ConserveOnline/Fishbase information on the American eel

NatureServe's Comprehensive Report on Anguilla rostrata

While Not Endangered, American Eels Face Numerous Threats - an article by Karl Blankenship from the Alliance for the Chesapeake Bay: Bay Journel

 

Nature picture credits (top to bottom, left to right): Photo © TNC; Photo © Garold W. Sneegas (American eel); Graphic © E. Blando/modified from Rob Slapkauskas American eel life cycle; Graphic© Elena Blando (American eel migration).