Eels have fascinated people since the ancient Greeks philosophized about their origins and the Romans dined on them as a delicacy. But from beginning to end, much of the eel’s life remains cloaked in mystery.
American Eels have the broadest diversity of habitat of any fish species in the world. Ranging from Greenland to Venezuela, they live in open ocean, marshes, estuaries, ponds, lakes, rivers, and streams, including every tributary of the Chesapeake Bay.
Eels are catadromous, meaning that they live in fresh water but reproduce in saltwater. Much of the eels’ reproductive process remains a puzzle, but scientists know that they begin and end their lives in the mysterious Sargasso Sea, an area of the Atlantic Ocean near Bermuda that has been a source of legend and myth since Columbus sailed through it on his way to the New World.
American eels support a significant fishery in the Bay. Long popular as bait, they are now caught and shipped live to Europe and Asia, where they are considered gourmet fare.
Although common in the Chesapeake, you could spend your whole life swimming and sailing the Bay and its rivers and streams and never see one. Nocturnal and timid, they spend most summer days burrowed into the mud. In the winter, they hibernate.
American eels primarily eat insects, crustaceans, worms, and other fish. They are not known to bite, and their sandpaper-like teeth are unlikely to do much damage, but they can eat mice and other larger animals by quickly spinning their bodies, breaking bones or snapping their prey. One eel caught in the Bay was found with a rabbit’s foot in its stomach.
American eels in the Chesapeake reach an average size of about two and a half feet, with females generally growing larger than males. In some places, females can grow to five feet. They absorb oxygen with their gills and through their skin, and can survive out of water for a brief period, especially in rainy or wet weather.
Eels’ lives have four distinct phases. They hatch in the Sargasso Sea as larvae called leptocephali, where floating with the currents, they begin their journey towards the eastern coast of North America.
Next, they reach the “glass eel” or “elver” phase, growing to three to four inches and moving into estuaries. In most states, including Virginia, it is illegal to catch American eels in the glass eel stage.
Most of their lives are spent in the third, “yellow eel,” stage, before they reach sexual maturity and begin the transformation to the last stage of their lives, know as the “silver eel” phase. During the silver phase, their bodies undergo profound physical changes in preparation for the long journey back to their spawning grounds in the Sargasso Sea.
American eels generally arrive in Chesapeake Bay waters from March to June, during their “glass eel” phase. It takes an eel anywhere from five to twenty-five years to reach maturity and become a “silver eel.”
Mature eels in and around the Chesapeake Bay begin their migration back to the Sargasso Sea in the autumn and reach their spawning grounds around January. Females can lay ten to twenty million eggs in one season. Though American eels are known to spawn in the Sargasso Sea, no adult eel has ever been seen or caught there. Scientists believe it’s because the eels’ spawning grounds lie six thousand feet beneath the surface of the sea.
In recent years, American eels have shown signs of population decline throughout the east coast, including the Chesapeake Bay, considered “the heart of the eel population.” Eels spawn near the end of their lives meaning that early mortality eliminates an eels’ chance to reproduce and contribute to the population. Interestingly the final days of the American eel’s life have never been observed in nature.
Fishing pressure, pollution, and parasites all present challenges to eel survival. Weakening ocean currents and their effect on larval dispersion are also implicated as causes for decline. In the glass eel (elver) stage, American eels have been know to wiggle up wet walls of dams and slither over moist, grassy areas to get around obstacles. Nonetheless, dams may impede eels’ ability to move from saltwater to freshwater rivers and back again, as they begin migration to the Sargasso Sea to spawn.
In November 1999 the Atlantic States Marine Fisheries Commission’s Eel Management Board approved a management plan to improve eel survival during their migration to the ocean in the hopes of boosting spawning. The plan includes restrictions on the fishing season, catch size, and gear, as well as plans to improve eel movement at dams. In February 2006, with eel populations still in jeopardy, the Board approved an addendum to the plan requiring a catch and fishing effort data monitoring program. A second addendum, which proposes more management options to increase the number of silver eels (adults), is currently under review.
Maryland Sea Grant
Marine Notes, May-June 2001
Maryland Department of Natural Resources
Virginia Institute of Marine Science
Counting Virginia's Juvenile Eels