The Amazing American Eel

On January 20th, The Haddam Land Trust sponsored a presentation about the American Eel as part of its annual meeting. Stephen Gephard, Supervising Fisheries Biologist with the DEEP, gave a fascinating presentation covering the natural history and conservation efforts of eels in Connecticut. The following is from my notes on the presentation and a little bit of investigation on the internet.

Eels are classified in the Order Anguilliformes. There are approximately 800 species of eel around the world, but interestingly, all of the eels living in the waters of the North American belong to one species named Anguilla rostrata, the American Eel.There are no regional differences between eel captured in Maine and eel captured in Brazil. This genetic homogeneity is called panmixia.

An American Eel begins life as an egg in the Sargasso Sea. Eels have never been observed mating but it is thought breeding occurs in the depths, at or near the bottom of the ocean. There is a deep depression in the ocean floor of the Sargasso Sea where it is believed American eel spawn.The hatched larvae, called leptocephali, drift on currents of the gulf stream for up to a year. Contact with the continental shelf triggers their transformation to the "glass eel" stage, in which they resemble a transparent ribbon of celophane with eyes. Glass eels begin to arrive in Long Island Sound waters in February and will number in the billions.

An interesting side note on glass eels involves the story of glass eel fisheries in America. Although eel aquaculture exists throughout the world, such enterprises aren't farms in the traditional sense. Consider that no one has yet been able to breed eels in captivity. Stocking programs therefore rely on wild captured glass eel, which have floated in from the deep ocean close to shore where they can be caught in nets. The eel are then sent overseas to farms in Asia and Europe where they are raised to harvest size. In 2010, Europe banned export of its native eel species and listed it as endangered. That, along with Japan's shrinking eel industry increased the demand for American eel and spurred a kind of "eel fever" along the Atlantic coastline where the price for glass eel spiked to over $2,000 a pound. American eel populations naturally suffered from increased fishing to the point where most states have now banned eel glass fisheries. Only Maine and South Carolina continue the practice.

Glass eel can remain in their transparent form for up to 3 years. When they enter fresh water rivers and streams their new diet triggers activation of pigment cells and they turn a greenish-brown color. They are called 'elvers' at this stage and are not sexed. They arrive in streams in June and travel at night climbing up over dams, rocks, through mud, and even wriggling through wet grass to continue upstream. They can move up a fully vertical surface if it is wet, with water levels low enough to not wash them away, and has enough texture for their bodies to use as 'footholds' much the way a rock climber uses depressions in rock to climb a rock face. 

When the elver finds it's preferred 'home' it will stay and live there for twenty years or more. It will also change color, losing the brownish-green and taking on a more brown-yellowish hue. It begins this transformation when it grows larger than 6 inches long. Yellow eels will eat anything, including large aquatic insects, worms, small fish and fish eggs, frogs, and dead animal matter. They are not voracious hunters, but are opportunists, known to visit captured or dying fish, swim up the female fish vents and eat the eggs out of them.

Sexual maturity occurs near the end of their life cycle. Sexual differentiation depends on density, higher density favoring male development and lower density favoring female development. In Connecticut all of the eel living in streams and their tributaries will be female. After sexual maturity the eel will then undergo its last transformation, preparing its body to return to the Sargasso sea to spawn. Eyes become bigger and more attuned to blue. The digestive system degenerates because once they enter the ocean an American Eel will no longer feed. As well, its body increases fat reserves to fuel that long journey. And it will change color once again, turning dark gray above with a white belly, becoming what we call a "Silver Eel."

Threats and Conservation in Connecticut
The main threats to this species in our state are dams, hydroelectic plants, and the water treatment facilities associated with reservoirs. Dams, depending on their construction, can prevent migrating elvers from continuing upstream. Hydroelectric and water treatment plants employ turbines which migrating Silver eel can swim into and become crushed. This is the case with the Groton reservoir in Southeastern Connecticut. Hundreds of eel get trapped here, able to climb up the dam when water levels are high but unable to get out in summer and autumn when water levels are low. 

Fortunately for Connecticut eels, the Fisheries Division of the DEEP has been working with private dam owners and water companies to devise ingenious methods of helping eel up dams and keeping them out of turbines. One method utilizes a pegboard like ladder for glass eel and a small rock ladder for larger eel. Another uses a PVC pipe stuffed with a length of twisted fishnet. The Groton reservoir is testing an assembly that diverts migrating eel away from the turbine into a pipe which spits them into a bucket which can be carried to the other side of the dam. 

The American eel is an important species with a fascinating life cycle that deserves continued research, conservation -- and appreciation. 

Posted by: Laurie Gorham