The US Military Gave Out Shark Repellent For Years. . . So Why Did They Stop?


On July 30, 1945, torpedoes from a Japanese
submarine split the U.S.S. Indianapolis in half, sinking it in 12 minutes. Over 200 sailors went down with the ship. Around 900 survivors were left adrift at sea
for 4 days. Dehydration and hypothermia killed 100s, but
floating in the open ocean it wasn’t long before sharks found them. One survivor–a 20-year-old Marine–recounted
seeing shark fins swimming around them, hearing blood-curdling screams, watching bodies get
sucked under, and seeing empty life vests pop back up to the surface. It’s impossible to know how many died by shark
attack but rough estimates range from a few dozen to 150 people. Many consider this the largest shark attack
in history. And it took a toll on Navy morale. Soon the US military started handing out a
chemical shark repellent. For the next few decades this little pouch
was standard issue for pilots, sailors, and even astronauts. But what none of those people knew at the
time was the shark repellent didn’t actually work. So, today I’m going to tell you the bizarre
story of the U.S. government’s obsession with shark repellent and why they handed out
something so useless to so many people for decades. OK, so by the time the USS Indianapolis happened,
the government had already sunk over a million dollars in today’s money into shark repellent. Why? It’s not totally clear. Jaws and Shark Week didn’t exist yet, and
Navy records indicate very few of their men had been attacked between 1907 and 1942. But stories can be more powerful than statistics,
and the stories were often grisly. In 1941 a Navy plane went down in the Pacific
after running out of gas. The pilot swam to shore for hours, dragging
his dead comrade, followed by sharks that ended up tearing off one of his deceased friend’s
limbs. Supposedly, Henry Field, President Franklin
Delano Roosevelt’s resident anthropologist, freaked out when he heard this story, called
up FDR, and convinced him that the military needed to develop shark repellent. The government began work on shark repellent
in 1942, led by what’s now the CIA. Back then, shark scientists didn’t exist. So they asked a guy named Stewart Springer–a
commercial fisherman and chemical technician–to lead the shark repellent team. Since man-eating sharks are hard to study
safely, Springer used dogfish in the early experiments. Dogfish are technically sharks, but they’re
the size of… small-ish dogs. The first chemical the team tested was rotenone,
which had previously been shown to kill goldfish at pretty low concentrations. Rotenone works by blocking cellular respiration–the
process where sugar and oxygen are converted to carbon dioxide, water, and energy in your
cells. With rotenone around, the fish can’t take
up, or use the oxygen in the water that surrounds them, so they basically suffocate and die. Good idea in theory, but in practice, rotenone
failed spectacularly as a shark repellent–the levels required to kill dogfish would kill
humans too. So the team tried other well-known poisons,
like sodium cyanide and the anaesthetic quinaldine, both of which did nothing to repel the sharks–they
just ate them and died later. So the team decided to try something a bit
different. Springer had heard that fishermen would hang
dead sharks off their boats to scare off live ones. So he and his team took a bunch of rotten
shark meat, ground it up, and used that to try and repel sharks. The team declared success, but the government
was skeptical, so they brought in chemists to identify the compounds in this “shark
concentrate” that might be doing the job. The chemists singled out ammonium acetate
as the likely active ingredient. And there had been some previous work showing
that copper could discourage fish from eating. So the team decided: LET’S PUT THESE THINGS
TOGETHER, and make copper acetate. Unfortunately, copper acetate only seemed
to work in very large amounts. So the team decided to add a third ingredient:
a black dye. They reasoned: If the sharks can’t see,
they won’t attack. They called their new concoction SHARK CHASER. Did Shark Chaser actually work? It depends on what “work” means. Did it chemically repel sharks? Not really. Sharks would stop feeding while the dye was
visibly present in the water, but as soon as it dissipated — which could be within
minutes — the sharks would return to their meal. So if you were adrift at sea for hours, let
alone days, you’d be out of luck. But at this point the government had already
tried over 100 substances and this was the best repellent out of all of them. The important thing was that they had something
they could pass out to sailors and pilots to make them feel safer and boost morale. But some people were concerned that giving
out Shark Chaser would do the opposite: freak people out and LOWER morale, so they also
issued a guide called Shark Sense that included information and comics to ease people’s
fear of sharks. But then, the U.S.S. Indianapolis disaster happened. And the government had to do something, so
they started putting Shark Chaser everywhere. For the next 30ish years, you could find it
in life jackets and on lifeboats, planes, ships, and even on spaceships. People had known that it was just a placebo
for years, but it took until the mid 1970s for Shark Chaser to officially be deemed useless
by the US Navy. But interest in developing an effective shark
repellent never fully died down. In 1974, just as the US military was moving
away from issuing Shark Chaser, researchers discovered that sharks were repelled by a
fish called the Red Sea Moses sole, which was secreting a compound called pardaxin. This sole releases pardaxin when it’s threatened. It creates holes in cell membranes and seems
to target a shark’s gills. Their movement quickly becomes irregular and
their jaw freezes in place. Problem is, pardaxin is hard to store and
is quickly diluted when dumped in the ocean, so it would really only be effective if you
sprayed it right into a shark’s mouth. The take-home from all of this? It’s really hard to find a chemical repellent
that works. In the open ocean, most chemicals dissipate
quickly. So, for the past couple decades, researchers
have been trying to figure out ways to make potential chemical repellents stick around
longer, like by combining pheromones with slow-release polymers. They’re also developing technologies to
disorient sharks by using magnetic fields to mess with the shark’s sensory system. But the truth is, we’re much more dangerous
to sharks than they are to us. In 2018 there were 100 shark attacks worldwide–34
of which were human provoked and only 5 of which were fatal. That gives you a less than 0.00000001% chance
of even being attacked by a shark. You’re much more likely to be struck by
lightning or killed by a dog. At the same time, about 50 million sharks
are accidentally caught every year by commercial fisheries. And many die. So, scientists are already testing longer-lasting
shark repellents to steer sharks away from commercial nets–and results look pretty promising. So promising that there are already US fishing
fleets trying it out. So over the past 75 years, shark repellents
have gone from completely useless, to sorta kinda protecting us from sharks, to hopefully
protecting them from us. What are we made of? How did the universe begin These are the kinds
questions that scientists at Fermilab, America’s premiere particle physics lab, are exploring. Visit Fermilab with Matt O’Dowd from Spacetime
in an exclusive episode over on the PBS video app. You don’t even have to leave the comfort
of your couch. If you live in the United States you can download
the PBS video app using the link in our description and stream the best of PBS shows, including
4000 other educational series like Nova, Frontline, and Ken Burns’ documentaries. And for those of you outside the US, no worries,
the episode will be up on Spacetime’s YouTube channel in mid-January.

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