The life cycle of the American eel (Anguilla rostrata) is as complicated as its journey from the Sargasso Sea to Long Island Sound. American eels hatch as tiny, leaf-shaped larvae in the Sargasso Sea, a unique region in the North Atlantic Ocean bounded by four major ocean currents.
The first phase of their lives includes a journey thousands of miles long to the Atlantic coast. To get there, the larval eels quite literally go with the flow, drifting on ocean currents for nearly a year. Those that are picked up by the Gulf Stream are swept along the eastern seaboard of North America and may eventually be funneled into Long Island Sound.
When they reach the continental shelf off the Atlantic coast, the eels undergo their first metamorphosis, becoming tiny, transparent “glass eels.” Once they arrive at coastal rivers and streams, it’s time to go against the flow. The young eels begin swimming upstream toward fresh water, developing pigment and darkening into elvers.
A note about fish handling: Fish shown out of the water were collected and handled by trained staff under appropriate scientific collection permits. Fish were handled using practices designed to minimize stress.
As they swim farther upstream in search of freshwater habitat, they gradually mature into yellow eels. They remain in the yellow eel stage for 10 to 30 years before undergoing their final transformation into silver eels. Their eyes, nose, and fins grow, skin thickens, and their digestive systems begin to shut down as they prepare for the long, grueling trip back to the Sargasso Sea.
Swimming upstream isn’t the only way these fish go against the flow. Their unusual migratory behavior also challenges the norm. Most migratory fish are anadromous, meaning they spend most of their lives in salt water and travel to fresh water to spawn. American eels are catadromous and do the opposite: they spend much of their lives in fresh or brackish water before migrating back to the salty ocean to spawn. In fact, they are the only catadromous fish in North America.
Home to the famous Bermuda Triangle, the Sargasso Sea holds another secret: exactly where and when American eels spawn. Despite decades of research, no one has ever observed American eels spawning in the wild. Scientists know they breed there because their smallest, youngest larvae have been found in the region. Only recently have satellite tags attached to eels provided direct evidence that adults make it back to the Sargasso Sea.
American eels that win the ocean-current lottery and end up in Long Island Sound become an integral part of the ecosystem.
Once here, they fill roles as both consumers and prey. As consumers, they are opportunistic eaters – scavenging for dead fish and other animals while also hunting small crustaceans, fish, and insects. They are also an important food source for predators, including birds and larger fish such as striped bass.
American eels are also an important indicator of ecosystem connectivity. Because they begin their lives in the ocean and migrate upstream into fresh water, their presence, or absence, in upstream areas can serve as a report card on whether rivers and streams remain connected. Dams and other barriers can make that journey difficult or impossible, while fish passage projects and barrier removals can reopen habitat that eels and other migratory species depend on.
Assessed as Endangered on the International Union for Conservation of Nature (IUCN) Red List, the American eel’s future depends in part on the health and connectivity of the freshwater systems where it spends much of its life.Protecting water quality, restoring habitat, and reconnecting rivers and streams can help give American eels the healthy waterways they need to complete their life’s journey spent going with the flow, against the flow, and sometimes, against the odds.
Sign up to receive our newsletters and updates. Choose the topics that interest you most!
"*" indicates required fields