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First adult American eel documented in Sargasso Sea

Some 30 species of eels spawn in the Sargasso Sea, but only two return to live out their days in fresh water.

By Brooks Hays
First adult American eel documented in Sargasso Sea
A photo of one of the tagged eels shortly after release. Photo by Jose Benchetrit/CC BY-ND

QUEBEC CITY, Oct. 27 (UPI) -- The first time in history, an adult American eel has been spotted and documented in the Sargasso Sea. The discovery brings a bit of closure to a scientific mystery more than 100 years old.

Scientists have long documented the presence of eel larvae in the Sargasso Sea, suggesting the little-understood species travels there to spawn. But an adult had never actually been seen there until now.

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A team of scientists in Canada affixed satellite trackers to 22 eels captured in Nova Scotia and 16 from the St. Lawrence Estuary. The effort was led by Julian Dodson, a professor at Laval University, Canada's oldest educational institution.

Several weeks after capture and release, 28 trackers resurfaced and pinged orbiting satellites, revealing their location in the middle of the Atlantic. The eels all took roughly the same path to the Sargasso Sea. Ocean data suggest the eels used differences in temperature and salinity to find their way to the spawning grounds.

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The Sargasso Sea is a huge gyre in the middle of the North Atlantic, bounded by several large ocean currents. Its water is bright blue and remarkably clear. It's the only sea not defined by land boundaries. It is named for a widespread free-floating seaweed called Sargassum, which serves as habitat for a variety of marine species.

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Scientists don't know exactly why the American eel (Anguilla rostrata) travels so far to spawn. There must be something special about the sea to inspire these odd-looking fish to swim some 1,500 miles in just 45 days.

Trackers showed the eels traveled east from Quebec to the edge of the continental shelf and then headed south to the sea.

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"Our data nonetheless shows that the eels don't follow the coastline the whole way, they can cover the route in just weeks, and they do go to the Sargasso Sea," Dodson said in a press release. "We knew that millions of American eels migrated to reproduce, but no one had yet observed adults in the open ocean or the Sargasso Sea. For a scientist this was a fascinating mystery."

Some 30 species of eels spawn in the Sargasso Sea, but only two return to live out their days in fresh water -- the American eel and the European eel.

The American eel is an endangered species. Its numbers have declined over the last several decades with the construction of dams along many of the East Coast's major rivers.

The journey of the American eel was detailed in the journal Nature Communications.

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