Eel Migration to Sargasso Sea Tracked for the First Time

A tagged eel, one of which made it all the way to the Sargasso Sea, revealing the route the animals take to get there for the first time. José Benchetrit, CC BY-ND

American eels (Anguilla rostrata) used to be so plentiful in some parts of the Northeast that they formed solid masses over the top of rivers. These days, they're much harder to find, mostly because they've lost 80 percent of their habitat due to damming and development.

Scientists have long known that the creatures live their adult lives in the freshwater rivers of northeastern North America. But it's presumed that they travel hundreds of miles away to breed in the Sargasso Sea, an algae- and flotsam-rich area in the middle of the Atlantic Ocean. No actual breeding has been observed, nor do researchers know exactly how they get there, but scientists have found American eel eggs there, as well as adult females. After the young are born, they somehow make their way back to eastern North America, where they live their lives as adults in freshwater rivers.

For the first time, researchers have found some hard evidence for this migration, after tracking one American eel for the entire route. Off Nova Scotia, Canadian researchers attached GPS trackers to 38 American eels, 28 of which were successfully tracked for a ways, although only one of them made it to the northern reaches of the Sargasso Sea, as scientists Julian Dodson and Martin Castonguay explain in a post in the Conversation. That intrepid eel migrated about 1,500 miles (2,400 kilometers) over the span of 45 days.

If this route proves to be taken by other eels, which is likely, it could help design policies to protect their safe passage, the duo write. But other enigmas, like how they breed and what they eat on their way to the Sargasso Sea, remain. "The American eel still has many secrets to reveal," they note. "We're continuing to satellite-tag open-ocean-migrating eels to unravel more of their mysteries."

The route the tagged eel took to the Sargasso Sea. Béguer-Pon et al / Nature Communications