The American Eel Biology

During the oceanic migration, American eels live in salt water. In the continental phase, they live in different salinity zones such as freshwater rivers, estuaries, and shallow marine waters. Eel densities decrease in larger rivers, and those that pass through hydroelectric dams are at risk of mortality due to turbines. They are highly adaptable in habitat use and primarily live on the substrate and bottom debris. The American eel spawns in the Sargasso Sea, and its larvae, known as leptocephali, drift toward the continental shelf and transform into small, transparent glass eels. These eels then become elvers (young eels) (see figure) as they develop pigmentation and move into inshore waters. The elvers can remain in shallow salt water, move into estuaries, or freshwater. As they grow, they become yellow eels, characterized by a dark back and yellowish belly. The sex of the eel is determined by environmental factors, with density being the primary influence. While females dominate in many areas of Canada, sex ratios are variable in rivers in the Maritime Provinces. Yellow eels can continue to migrate for many years, and they hibernate in mud during winter in all salinity zones. When they reach a certain size, their bellies turn silver, and they prepare for the spawning migration. The size at which this silvering occurs is larger in the upper St. Lawrence and Lake Ontario than in other areas, and these large eels are highly fecund and can make a significant contribution to the species' total reproductive output. American eels are long-lived, and population indicators typically include numerous year classes at stages other than glass eels/elvers.