There is an old saying that if all else fails 'you can always sell it as a boat anchor'.

And then there are 'shark repellents'. Interesting marketing scheme. Make a claim. If they don't get eaten you claim it worked. If they do there isn't anyone left to claim the product didn't work.

http://physicsbuzz.physicscentral.com/2010/08/physics-of-shark-attacks.html

The search for shark repellents has been a long one. Just before WW2 someone figured that a mix of iron sulfate, presumably a bad tasting substance to a shark, and a dense blue dye, which would obscure the shark's vision or look like a dark wall, would repel sharks. Sounded good but nobody really tested it. The US Navy bought loads of the stuff. The primary effect was likely that it made people who jumped into the ocean feel a bit more confident that, just maybe, they wouldn't end up as a shark's lunch.

An inside joke was included in the packaging. You had a half-pound or so of the powder in a packet. On the outside of the packet, in large block letters were the words: "LIFE JACKET REPELLENT". Notice the complete lack of any mention of sharks. Taken literally its intended use was to keep life jackets away.

Some time after WW2 testing was done and it was found that sharks were not put off by the the taste of iron sulfate or the blue dye. No effort was made to check if it kept hostile life jackets away.

Then again these units have magnets and/or EM fields. And everyone knows you can do anything with magnets or EM fields because they are 'high-tech'. It has yet to be shown that the sharks are as impressed as the gullible humans who buy these sorts of things.

It has been said that bears are ambulating garbage cans, and will eat anything.

I always assumed that sharks were pretty much the same. I also assumed that there might be two things that sharks wouldn't eat: anything metal that was larger than they are, or if you are completely encased in a metal container that is completely surrounded with sharp metal spikes, like a very large sea urchin.

But you really do have to watch out for those vicious life jackets...

Sue

> The search for shark repellents has been a long one.
> Just before WW2 someone figured that a mix of iron sulfate,
> presumably a bad tasting substance to a shark, and a dense
> blue dye, which would obscure the shark's vision or look
> like a dark wall, would repel sharks. Sounded good but
> nobody really tested it.
...
> Some time after WW2 testing was done and it was found
> that sharks were not put off by the the taste of
> iron sulfate or the blue dye.

No, they really did test it before deploying it in WWII.

An experiment in 1963 [7 - Experiment XII] found that while the WW2 repellent prevented whitetip sharks from taking bait in every experiment tried, it had negligible deterrent effect on grey sharks.

Some other post-WW2 tests found the WW2 "Shark Chaser" shark repellent (which was not iron sulfate, but rather a mixture of acetic acid and copper sulphate, called copper acetate or cupric acetate) ineffective.[1,2]

There was lots of US testing of potential repellents on sharks during WWII, and that's how they zeroed in on the copper acetate. [3,4,5]. Apparently some post-war Australian testing also indicated copper acetate was effective[6].

The man who instigated the WWII development of shark repellent says he instigated development of shark repellent in 1942 (during, not before WWII) and that extensive testing was done for the US navy (BuAer, specifically) on possible shark repellents: "We began by testing over 150 possible repellents one after another. Nothing worked." Contrary to the assertion that there was no testing, he said: "Chemicals were combined and tests with sharks run off Florida, southern California and Ecuador." After that, he said "we were ready to quit". Then someone mentioned that multi-day decomposed shark was repellent. "A small shark was killed, and every four hours as it decomposed, a piece of meat was tried as a repellent on the ravenous sharks in the big tank. Several days later the telephone jangled and a voice said: "We have it!"
"Two chemicals and the decomposing shark were combined. Production began. The 'shark repellent' in a waterproof belt container is now standard equipment for military personnel."[3]

While Henry Field doesn't cite which chemicals were used, this article,
http://marine-land.com/repellent.htm
which also discusses the WWII testing on dog sharks (the most common) says they were acetic acid and copper sulfate. They called the combination "copper acetate".)

There is more discussion in [4].

[1] A Review of Chemical Shark Repellents
http://www.colostate.edu/Depts/Entomology/courses/en570/papers_2006/tauchen.pdf

[2] The effectiveness of sodium lauryl sulphate as a shark repellent in a laboratory test situation
http://onlinelibrary.wiley.com/doi/10.1111
/j.1095-8649.1991.tb03096.x/abstract

[3] Field, Henry, "The Track of Man", pp. 329-331
http://books.google.com/books?&id=scdnAAAAIAAJ

[4] Thomas B. Allen,
"Shark Attacks: Their Causes and Avoidance" p. 207-210
http://books.google.com/books?id=O8qJf3QnEZ4C&pg=PA207

[5] MCBRIDE,A. F., AND A. H. SCHMIDT1,943. Final report on shark repellent experiments conducted in Ecuador. Conzm. on Medical Res., O f f . Sci. Rcs. Dcv.(declassified). { Cited in:
www.biolbull.org/cgi/reprint/104/1/28.pdf )

[6] WHITLEY, G. P., AND G. H. PAYNE, 1947. Testing a shark repellent. Australian Zool., 11:
151-157. ( Cited in:
http://www.archive.org/stream/biologicalbullet104mari/biologicalbullet104mari_djvu.txt )

[7] Feeding Behavior in Three Species of Sharks
http://scholarspace.manoa.hawaii.edu/handle/10125/4936