U.S. Fish & Wildlife Service American eel Anguilla rostrata

There are three species of freshwater The life of the American eel is believed to Classifying the American Eel eel, the American eel (Anguilla begin and end in the Sargasso Sea. Each Migration: rostrata), European eel (A. anguilla), winter, mature American eels return to Is it catadromous or anadromous? and Japanese eel (A. japonica), but spawn in these natal waters. the American eel is the only species of American eels were long considered freshwater eel found in North America. Eels gather here from across the species’ North America’s only catadromous range, such that individuals could breed fish—meaning born in the ocean, People have fished and farmed eels for with American eels from Greenland mature in freshwater and return to thousands of years, but until recent down to South America. This behavior the ocean to spawn. Anadromous fish, times, little was known about the eel’s perpetuates a single breeding population, like salmon, are born in freshwater complex life history. The American preventing the distinctions sometimes streams, travel to the ocean to eel has survived multiple ice ages and found in species that live in different mature, and return to freshwater to seems to be equipped to withstand geographic areas. spawn. the cycles and fluctuations inherent in ocean dynamics. Some scientists Leptocephali: While some American eels swim up consider the highly adaptive American After fertilization, the eel eggs eventually freshwater streams to mature, others eel to have the broadest diversity of float to the ocean surface and hatch into remain and mature in both estuarine habitats of any fish species in the world. small, transparent larvae that are shaped and marine waters. The discovery like willow leaves. These larvae drift of eels in both marine and estuarine The American eel hatches in the ocean with the Gulf Stream and other currents, habitats led biologists to revise that waters of the Sargasso Sea, 2 million taking about a year to reach the Atlantic description to facultative catadromy, square miles of warm water in the coast. meaning they may be found in North Atlantic between the West Indies freshwater or saltwater during and the Azores. This snake-like fish Glass eels: maturation. uses currents to move from its natal By the time they reach the coast, the waters to find homes throughout its larvae have developed fins and the shape Eels can absorb oxygen through their range, from Greenland south to Brazil. of adult eels. In this phase, these juveniles, skin and gills, allowing them to travel known as glass eels, are still transparent over land, particularly wet grass or Eel Migration and Life Cycle and are about 2 to 3 inches long. mud. Eels also can cover their entire During its lifetime, the American bodies with a mucous layer, making eel changes habitats and undergoes Elvers: them nearly impossible to capture by several physical phases, known as At this stage, eels migrate to brackish hand—making “slippery as an eel” metamorphoses. waters and begin to develop gray to more than just a figure of speech. green-brown pigmentation. Many elvers have been known to move to inland habitats through tidal rivers, yet some remain in estuaries or brackish habitats or in marine waters. This phase includes all eels that reached more than 4 inches in length.

Yellow eels: Before the final maturation stage, they become yellow eels—sexually immature

adults that are actually yellow-green MFRO/USFWS

MFRO/USFWS to olive-brown. In their yellow phase, Silver eels collected in Shenandoah The eel is a smooth and snake-like fish American eels are nocturnal, swimming River to be radio tagged for a tracking that feeds on insects, fish, mollusks, and feeding at night. In freshwater, they study. crustaceans and dead animal matter. find homes in streams, lakes, ponds and rivers, particularly where they can hide Threats to the American Eel under logs and rocks. Potential impacts to American eels vary in scope and severity across After 3 to 40 or more years of living in the species’ range. American eels no freshwater, brackish waters, or marine longer have access to much of their waters, the yellow eels begin to sexually historical habitat because dams and mature. Eels that remain in estuarine other obstructions in rivers block and and marine waters undergo the same divide habitat and migration corridors. changes but mature earlier than those in Localized population declines are also freshwater. attributed to mortality in hydropower plant turbines, degradation of current Silver eels: habitat and overharvest.

American eels begin sexual Office/USFWS Resources MarylandFishery differentiation at a length of about 8 to An Asian parasite (Anguillicola Juvenile eels, elvers, in a ramp for 10 inches. Depending on a variety of crassus), likely introduced into the passage study at Conowingo Dam. factors, which can include population range of the American eel through density, eel growth rate, and water aquaculture practices, infests some eels’ Conservation organizations have salinity, they become male or female swim bladders—an internal gas-filled targeted projects removing dams that silver eels with dark coloring, bronze- organ that regulates a fish’s buoyancy. interrupt historic eel migration routes. black backs and silver undersides. Once eels mature and begin their In concert with other natural resource Female American eels can grow to 5 feet return swim to the Sargasso, a non- agencies, the Service has also worked to in length, and males usually reach about functioning or even somewhat impaired mitigate adverse impacts to eels. These 3 feet. swim bladder may result in individual measures are specified during the deaths prior to spawning. licensing or relicensing of hydropower Silver eels complete sexual maturation projects and can include the addition of as they return to the Sargasso Sea to Fishing pressure has had some facilities like eel ladders to safely pass spawn. They undergo amazing physical impacts on the American eel. Glass eels fish and eels upstream. Eel ladders are changes enabling this return to the cyclically fetch a high price on the Asian usually designed to allow eels and other ocean, transforming the eels from market, and this young life phase of fish to swim over barriers using an shallow water, bottom dwellers to ocean American eels was heavily harvested ascending ramp. travelers. in the U.S. in the 1970s. This may have contributed to regionally recognizable Eel migration is monitored at various Eels cease to feed during ocean declines. Harvest can be especially areas both upstream and downstream migration, and their gut begins to detrimental because of the eel’s slow to help understand and optimize eel degenerate. To fuel the long ocean swim, maturation process. passage inland and to the ocean. Where their fat reserves increase. Eyes double eel passages have been built, eel in size and become more sensitive to Climate change may also be impacting passage numbers are usually recorded blue, enhancing vision in deep water. American eels and their habitats, but to to better understand population status. Blood vessels feeding their swim what extent is not yet known. bladders increase in number, allowing Other conservation actions include increased gas deposition and reduced Conservation Efforts and Plans restrictions on eel harvest by U.S. loss of gas, both critical for buoyancy. Despite these challenges, American eels states and by the federal government in remain in much of their vast historic Canada. The Committee on the Status Upon return to the Sargasso Sea, range. In some large coastal rivers, of Endangered Wildlife in Canada females release 20 to 30 million eggs eels are the most commonly found fish, designated the American eel a species that are fertilized by males. Once they occupying more aquatic habitats of special concern, protecting it under spawn, it is assumed that adult eels die, than any other species. the federal Fisheries Act and closing but researchers have never witnessed the harvest of eels in the Canadian eels spawning in the wild. Addressing threats to the American eel portion of Lake Ontario. and its conservation has taken several forms, from research and The U.S. Fish and Wildlife Service monitoring to activities continues to work with partners to increasing eel access better understand and conserve this to former habitat and remarkable species. spawning grounds. The Atlantic States Marine U.S. Fish & Wildlife Service Fisheries Commission has 300 Westgate Center Drive a fishery management plan Hadley, MA 01035 for American eels, and the Connecticut River Atlantic 1 800/344 WILD Salmon Commission is www.fws.gov currently developing a September 2011 Connecticut River Basin

Maryland Fishery Resources Office/USFWS Resources MarylandFishery American Eel Management Elvers climb Conowingo Dam on the Susquehanna Plan. River. These juvenile eels migrate to brackish waters, developing gray to green-brown color.