Illustration by Scott Brundage February 2022, ScientificAmerican.com 15oceans, from
Massachusetts to
Mexico to the Galápagos. The findings, pub-
lished in Ecology , show that fish-on-shark
chafing is more pervasive and widespread
than previously recognized. “It must serve
some ecological function to have evolved
across so many species,” Williams says.
The duration of the chafing events ranged
from a fleeting eight seconds to more than
five minutes. Sometimes a lone fish was
involved; at other times, an entire school
of 100 or more individuals took part. Many
sharks seemed not to care that they were
being used as a living back scratcher, but
some of the great white sharks contorted,
wiggled their bodies or did corkscrew dives,
seemingly trying to shake the other fish off. To
the researchers’ surprise, sharks were not
observed trying to eat the fish.
Jonathan Balcombe, an independent ani-mal behavior biologist
and author of What a Fish Knows ,
says chafing “is consistent with the aware-
ness, intelligence and opportunism of fishes
as shown by a growing body of re search on
their cognitive and emotional ca pac it ies.” It
is possible the fish simply enjoy the sensation
of rubbing against sharks’ rough skin, adds
Balcombe, who was not involved in the study.
There is “both anecdotal and scientific sup-
port for a therapeutic role of touch in reliev-
ing stress in fishes and other taxa.”
The authors acknowledge that the study
raises more questions than it answers—in -
cluding whether sharks get any benefit or
are harmed from chafing and why fish spe-
cifically choose sharks to rub against rather
than sticking with inert (and seemingly much
safer) rocks or sand. After all, Anstett says,
“you don’t see a lion’s prey scratching up
against a lion.” — Rachel Nuwerother side of such obstacles, he says, “you
need to undo the scattering and resolve
the [hidden] structures with very high
resolution.” The technique overcomes
those challenges at frame rates fast enough
for video, Ingle adds.
The process involves firing laser beams
with slightly different wavelengths past ob-
structions—be it off a wall or through some
translucent material—to strike a hidden tar-
get. The wavelengths that reflect back are
captured and superimposed to produce an in-
terference pattern that reveals the distances
of objects hidden from direct view. This pro-
cess draws from a technique called interfer-
ometry, which scientists have used to precise-
ly measure the size and shape of stars and cell
structures. Other forms of “non-line-of-sight”
imaging struggle with simultaneous speed,
high resolution and broad field of view. “Our
method combines all these attributes at the
same time in one method,” says Northwest-ern University physicist Florian Willomitzer,
lead author on the new study.
Willomitzer and his colleagues demon-
strated that they could capture images of mil-
limeter-sized letters beyond corners as well
as through hazy plastic plates. Whereas pre-
vious imaging methods iteratively scanned
thousands of pixels to compose a scene, this
process required only two exposures (each
taking just 23 milliseconds to capture) to scan
a near-hemispherical field of view.
Combining this technique with ultrasound
imaging could eventually let doctors see
around bones or view tiny blood vessels un-
der skin, Ingle suggests. Both researchers
say, however, that more work and testing are
needed to turn that vision into reality. Prob-
ing a slab of living tissue is harder than peer-
ing through thin plastic—but in 10 or more
years, Ingle says, this research could yield
a practical, commercially available way to
look beyond the line of sight. — Nikk OgasaIllustration by Scott Brundageoceans, from
Massachusetts to
Mexico to the Galápagos. The fi ndings, pub-
lished in Ecology , show that fi sh-on-shark
chafi ng is more pervasive and widespread
than previously recognized. “It must serve
some ecological function to have evolved
across so many species,” Williams says.
The duration of the chafi ng events ranged
from a fl eeting eight seconds to more than
fi ve minutes. Sometimes a lone fi sh was
involved; at other times, an entire school
of 100 or more individuals took part. Many
sharks seemed not to care that they were
being used as a living back scratcher, but
some of the great white sharks contorted,
wiggled their bodies or did corkscrew dives,
seemingly trying to shake the other fi sh off. To
the researchers’ surprise, sharks were not
observed trying to eat the fi sh.
Jonathan Balcombe, an independent ani-mal behavior biologist
and author of What a Fish Knows ,
says chafi ng “is consistent with the aware-
ness, intelligence and opportunism of fi shes
as shown by a growing body of re search on
their cognitive and emotional ca pac it ies.” It
is possible the fi sh simply enjoy the sensation
of rubbing against sharks’ rough skin, adds
Balcombe, who was not involved in the study.
There is “both anecdotal and scientifi c sup-
port for a therapeutic role of touch in reliev-
ing stress in fi shes and other taxa.”
The authors acknowledge that the study
raises more questions than it answers—in -
cluding whether sharks get any benefi t or
are harmed from chafi ng and why fi sh spe-
cifi cally choose sharks to rub against rather
than sticking with inert (and seemingly much
safer) rocks or sand. After all, Anstett says,
“you don’t see a lion’s prey scratching up
against a lion.” — Rachel Nuwerother side of such obstacles, he says, “you
need to undo the scattering and resolve
the [hidden] structures with very high
resolution.” The technique overcomes
those challenges at frame rates fast enough
for video, Ingle adds.
The process involves fi ring laser beams
with slightly diff erent wavelengths past ob-
structions—be it off a wall or through some
translucent material—to strike a hidden tar-
get. The wavelengths that refl ect back are
captured and superimposed to produce an in-
terference pattern that reveals the distances
of objects hidden from direct view. This pro-
cess draws from a technique called interfer-
ometry, which scientists have used to precise-
ly measure the size and shape of stars and cell
structures. Other forms of “non-line-of-sight”
imaging struggle with simultaneous speed,
high resolution and broad fi eld of view. “Our
method combines all these attributes at the
same time in one method,” says Northwest-ern University physicist Florian Willomitzer,
lead author on the new study.
Willomitzer and his colleagues demon-
strated that they could capture images of mil-
limeter-sized letters beyond corners as well
as through hazy plastic plates. Whereas pre-
vious imaging methods iteratively scanned
thousands of pixels to compose a scene, this
process required only two exposures (each
taking just 23 milliseconds to capture) to scan
a near-hemispherical fi eld of view.
Combining this technique with ultrasound
imaging could eventually let doctors see
around bones or view tiny blood vessels un-
der skin, Ingle suggests. Both researchers
say, however, that more work and testing are
needed to turn that vision into reality. Prob-
ing a slab of living tissue is harder than peer-
ing through thin plastic—but in 10 or more
years, Ingle says, this research could yield
a practical, commercially available way to
look beyond the line of sight. — Nikk Ogasaoceans, from
Massachusetts tomal behavior biologist
and author of What a Fish Knowssad0222Adva3p.indd 15sad0222Adva3p.indd 15 12/15/21 5:16 PM12/15/21 5:16 PM
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