People have been developing different forms of shark repellent for decades — the military even issued a chemical shark repellent called “Shark Chaser” to pilots, sailors and astronauts(!) from the end of World War II through the start of the Vietnam War. Thing is … it didn’t really work. Learn why they bothered passing it out or even created it in the first place.
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.
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?
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.