October 2017 Discover

24 DISCOVERMAGAZINE.COM

CLOCKWISE FROM TOP LEFT: HEATHER PERRY/NATIONAL GEOGRAPHIC CREATIVE; STAN HONDA/GETTY IMAGES; ROBERT ALEXANDER/GETTY IMAGES

at random — no natural selection dur-
ing breeding — and then lay millions of
eggs. Afterward, all the adults likely die.
The little orphan eels then venture back
to their species’ coast.
“These are tiny little creatures, and
they do not swim that well,” says ocean-
ographer Irina Rypina with the Woods
Hole Oceanographic Institute. Her
team modeled how eel larvae traverse
the Atlantic and found that the tiny fish
must swim their way toward currents,
which help them along to far-off shores.
Earlier this spring, an American-led
team of scientists explained how that
happens in the journal Current Biology.
The team let young eels swim around
a contraption that mimicked the mag-
netic fields found along the animals’
migratory path. Rather than guiding
the little swimmers toward land, the
researchers found infant eels have a
“map sense” that steers them toward
the Gulf Stream, which offers an easier
ride toward Europe. Another team,
which published results in Science
Advances in June, tested even younger
eels in a Norwegian fjord and found
similar magnetic navigation abilities.

CATCH AS CATCH CAN
Scientists hope that unraveling the eels’
secrets will help recovery efforts. Baby

eels, called elvers, now face a major

obstacle to survival. Elver fishing is

booming in Maine and along the East

Coast. The Japanese have obsessed over

“unagi no kabayaki,” a type of grilled

eel, since ancient times. So as global

fisheries have banned the capture of eels

to protect populations — Japan did so

after the 2011 tsunami — consumers

have turned to American eels. European

eels are also critically endangered.

American fishermen can now net

thousands of dollars per pound for the

live, squirming elvers. Once caught and

sold, they’re shipped to farms in China

and Japan, where they’re raised to

adulthood and sold globally for sushi.

That makes understanding the

natural migratory path crucial to

preserving the species. For instance,

knowing that eels in Spain and Sweden

are no different could add geographic

flexibility to reintroduction efforts.

And a better understanding of how

eels reproduce might one day let people

farm eels from birth, something that’s

currently impossible. But until cameras

catch eels spawning in the Sargasso

Sea, scientists can’t fully claim they’ve

put Aristotle’s mystery to rest.^ D

Eric Betz is an associate editor at Discover.

He’s on Twitter: @ericbetz

Scientists hope that

unraveling the eels’

secrets will help

recovery efforts.

Baby eels, called elvers,

now face a major

obstacle to survival.

Once they reach freshwater, juveniles become glass eels

(left). This tiny glass eel (above) was caught in a New York

creek during a population monitoring project.

Grilled eel, or unagi, is a Japanese favorite.

Notes

From

Earth