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American Eel Illustration © Duane Raver/U.S. Fish and Wildlife Service

Illustration of an American eel

One of America's Most Mysterious Travelers

Each autumn, as if by clockwork, hundreds of thousands of American eel (Anguilla rostrata) descend the rivers, estuaries and bays of the Atlantic Coast on their journey to the Sargasso Sea, a 2-million square mile region of warm water in the northern Atlantic Ocean.

The Sargasso Sea is where all American eels are born. While science has never witnessed the spawning secrets of the eel — where, what depth, how they reunite — it is known that a mysterious combination of the moon, the stars, magnetism and an exceptional homing ability all play a part in their ancient ritual.

After mating, the adult eels die. But over time, their newly laid eggs hatch billions of tiny larvae. Small, transparent and shaped like a willow leaf, the larvae are at the mercy of the ocean’s many currents. For nearly 12 months the larvae float through the ocean and toward the coast, encountering predators at nearly every twist and turn.

The eels that survive their ocean journey then begin the next phase of life: traveling hundreds of miles through estuaries and into freshwater systems along the Atlantic Coast. Eels may spend as many as 20 years within a watershed ascending rivers, crossing lakes and pushing toward headwaters.

Eel Facts

Adult eels have a long, cylindrical body and a snake-like appearance, save the single continuous fin running from the dorsal side to the pelvic area. Eels have a thick, slimy skin colored olive to brown above, yellowish on the sides and lighter below. Females average 24 to 36 inches, while the males are usually somewhat smaller.

In their freshwater homes, eels prey on or scavenge aquatic invertebrates, amphibians and fish. In turn, large predators such as bass, lake trout, fish-eating birds and mammals may eat them. Many eels are also caught by humans and used as used as bait for fishing activities or exported to support food demands in Europe and Asia.

One day, the Sargasso finally calls the eels back home. Their bodies turn to blackish-bronze, their eyes enlarge, they fatten and develop a thicker skin, and their digestive tract degenerates. Finally, one mysterious mid-autumn night, the eels once again descend from their river homes and make their way back to the sea.