October 2017 Discover

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Johannes Schmidt spent 25 years

chasing an enigmatic fish across

the Atlantic Ocean. The Danish biolo-

gist surrendered the hunt only after his

ship was torn to pieces on a Caribbean

coral reef. Schmidt was trying to

solve an ancient mystery about one of

nature’s strangest fish: eels. Aristotle

suggested the slithering species emerged

spontaneously from the earth. But by

the early 1900s, Schmidt and others

suspected eels bred in the open ocean,

instead of their lifelong freshwater

homes.

Schmidt’s early sea expeditions

stayed close to shore, casting nets off

European coastlines. Then, in 1904, he

caught a young eel south of Iceland,

implying the fish were indeed spawning

at sea. So Schmidt journeyed farther

into the open ocean.

The tinier the eels he found, the

closer he figured he was to their spawn-

ing grounds.

Eventually, he sailed from northern

Europe toward the Caribbean, ulti-

mately catching dime-sized eels near the

Sargasso Sea. It’s an enormous patch

of seaweed in the southwest Atlantic

Ocean. He guessed this calm stretch of

ocean was the eel asylum —

the place where European and

American eels are born, spawn

and die.

It’s been nearly a century

since Schmidt’s hypothesis, but

eels still haven’t surrendered

their secrets. We now know

that American eels inhabit

streams, lakes and rivers from

Venezuela to Greenland, and the simi-

lar (yet genetically distinct) European

eels live anywhere from Norway to

North Africa. But scientists still haven’t

seen these eels spawning. So, that eel

you ate on your sushi roll? No one

knows for certain where it was born.

THE HUNT

In recent years, however, scientists have

been closing in. Like Schmidt,

they’re trying to track eels

as they migrate back to the

Sargasso Sea. To crack the

case, Canadian researchers

devised a way to attach satel-

lite tags to the eels to trace

their routes during the 1,500-

mile swim from shore.

Along the rugged coast of

Nova Scotia, scientists caught

several dozen eels in 2014.

They dumped the slithering

fish into a water tank in the

back of a pickup truck and

drove to the little village of

Bay St. Lawrence. There, the

team attached satellite track-

ing tags — picture several feet

of eel dragging a huge fishing

lure — and put the fish back

in the Atlantic. They’d tried a

similar feat the two previous

years, releasing the squirm-

ing fish from a nearby estuary,

but sharks ate all the eels

before they reached the open

ocean. Just eight of the 38 eels

released over the course of the

three-year experiment even

made it to the ocean.

Biologist Mélanie Beguer-

Pon of Quebec’s Laval

University says tracking

The Vanishing Eels

Scientists reveal new clues about one of

nature’s most mysterious migrations.

BY ERIC BETZ

European eel

GULF OF

MEXICO

ATLANTIC OCEAN

SARGASSO

SEA

NORTH

SEA

Johannes Schmidt

For a century, scientists have suspected American and European eels swim vast distances to spawn in the

Sargasso Sea. But until recently, no one had ever seen an adult eel there, or any signs of spawning. Now

researchers are trying to unravel how they do it.

Paths to the

Sargasso Sea

American eel

European eel

Ocean currents

Sources: USFWS, NOAA, Cefas

Notes

From

Earth