Lots of Shark Talk lately... Teckie question for deep thinkers

[supthecreek]

Info from Wikipedia:
Great white sharks, like all other sharks, have an extra sense given by the Ampullae of Lorenzini which enables them to detect the electromagnetic field emitted by the movement of living animals. Every time a living creature moves, it generates an electrical field and great whites are so sensitive they can detect half a billionth of a volt. Even heart beats emit a very faint electrical pulse. If it is close enough, the shark can detect even that faint electrical pulse.

Electronic Shark Defense System (ESDS)says:
Longtime Honolulu surfer Wilson Vinano Jr. says he has come up with a way for surfers and divers to fend off sharks.

He has created the Electronic Shark Defense, which sends out an electric pulse that short-circuits the gel in a shark’s nose.

“What our product does is shock and thus interrupts a shark,” he said.

My Question:
If sharks are ATTRACTED by electrical impulses.... and the ESDS repels them with electronic impulses...
is it a fair assumption that the ESDS may actually ATTRACT the sharks that it ultimately repels? And if so... does that create a greater risk for the other people near you that are NOT wearing an ESDS?

I posed that question to the ESDS folks but I have not heard back from them,

I just would not want to wear something that would protect me, but put others in jeopardy.

[stoneaxe]

Sounds like a pretty good marketing strategy......

[H2Oman]

I sometimes walk in the forest.  I hear that bear, wolf, cougars and other life threatening beasts live there.  Can anyone get me Troy Hurtubise's contact number?


(i'm only teasing...its your life)

[supthecreek]

You know what H20man???... now I'm pissed off
Is that your cheap shot way of calling me a boy in a bubble?

You don't know diddly squat about me.

I figured someone would have fun with me over this question...
But your ignorant reply says a lot about you.

You are welcome to come walk with me in the places I go and the things I do... you couldn't keep up... all my life I've done things that scare the crap out of me... but I don't back down.

In case you can't tell... you really pissed me off

NO.... I don't like the fact that Great Whites are showing up where I surf... in great numbers.
YES... I will continue to surf at Dawn... and alone... and on foggy or crappy days... or if it's 8 below zero.
But I DON"T have to be stupid about it.
Are you a coward because you have an AIRBAG in your car?

Lets see what you would do if this was YOUR break

9 Great Whites in the last 3 days... all within sight of where WE surf.... NOT where YOU surf.
AND they are ALL inside the surf line.... NOT a mile out to sea
Not to mention they are showing an interest in floaty things at MY beach... NOT yours... Hero.

[H2Oman]

Don't be pissed off...just kidding didn't come through strong enough in my last sentence.  

Troy Hurtubise was a funny cat (especially to us Canadians) and its not often that a window opens to pay tribute to him and his suit.  As you can tell, I didn't put a lot of deep thinking into the post.

Damn internet.  

[finsider]

Supthecreek, your question is one that I have wondered as well.  The only logical way I can think of it would be to compare it to our hearing.  Sharks can "hear" all electrical impulses but these supposed repellent devices could be akin to those LRAD noise devices the military use. There are plenty of things I can "sense" that repels myself, the scent of my own feet after a long day included  It still amazes me how little we know about these creatures, I would love the chance to do research work with them.

Also H20man did say he was only teasing, but I actually think the bear suit is cool.

[PonoBill]

It's not likely that it's an attractor. Sharks use their abilities to detect electrical impulses to locate struggling fish and other game. the signal prey generate is low intensity and randomly noisy. Most of the electric shark repellent systems use a DC square wave with a fairly high voltage.  This signal will be painful to the shark at any distance they can detect it. The shark equivalent on fingernails on a blackboard. Not an attractive sound no matter how quiet it might be.

Different sharks are sensitive to different frequencies, so the effectiveness is not universal, and some sharks have no ampullae, or low sensitivity. But square waves contain a very large number of harmonic frequencies so they will be broadly effective and most of the shark you'd care about have sensitive ampullae.

Electrical shark repellants have been around for many years. They work pretty well. You'd probably be best off with the ones that integrate with a leash. You need a long separation between the electrodes for the sheet resistance effect to be strong.

[supthecreek]

Thanks Bill and finsider,  That's the kind of useful information I was looking for.

[Ichabod Spoonbill]

Shark repellants of any sort have been traditionally very unreliable. They work by overwhelming or dimming one of the shark's senses. but the problem is that sharks don't just hunt with one sense. They use smell, sight, vibrations, and that electro-sense.

We all know about how blood in the water gets a shark excited, and they can smell that in very small amounts. They see you too even though sight isn't their main hunting sense -- it's only used at short range. One of the big issues is that a person swimming gives off a lot of vibrations that are picked up by a shark's lateral line sense -- they literally feel you swimming. There isn't much defense against that short of swimming in a bag. Then there's the Ampullae of Lorenzini.

I just wouldn't put any trust in a shark repellant. The US Navy has been experimenting with repellants for a long time. They have a vested interest in them because their downed sailors and aviators go right into the water. Remember Quint's story about the USS Indianapolis? That was a real sailor's  account he told. I may be a little out of date here, but I don't think they've found anything that really worked

Great Whites are incredible creatures, evolved to eat (mostly) medium sized mammals. The good news (sorta) is that we don't taste very good to great whites. Seals are very fatty, which is what Mr. Bruce wants to eat. Humans aren't as fatty, so usually the Great White takes a bite, then leaves. The problem is with a four meter shark that's a hell of a bite!

I think the truth is that we're stuck with these sharks. Common sense is our best defense.

[Weed]

It's a good question Creek because I hate to say it but the shark problem is only going to get worse due to the increase of seal population. Back track 15-20 years ago you rarely had a great white sighting. As the seal population increased whitey started to show up in September, then late August and now June/July.

Question: What brought the seals here? Someone mentioned once "The Cut" in Chatham opened up after a nasty Noreaster that brought in the baitfish which in turn brought in the seals, then Whitey. I wonder what would happen if a major storm came and closed The Cut and reshaped the landscape of the coastline?

[PonoBill]

It makes great sense for the navy to lead the charge in developing shark repellent, but government agencies--especially military--and "sense" are not a given.

The statistics are misleading because of inherent bias (most traffic accidents occur within 20 miles of home--well sure, that's where people are most of the time) but even for a person that spends the majority of their time in sharky water, you're in much greater danger on the drive to the beach than on the water.

But if it makes you feel better to buy an electronic shark repellent, get one. It might help.

[surf4food]

This is the second time I’ve posted this but anyway I would use what Batman had.

[Brendon]

There were recent tests done on a Shark Shield which works on more oress the same principles. Tests were done on a static bait in Aus and on a moving seal decoy off Seal Island in False Bay. It seems that the shield works pretty well with Great Whites but not 100% safe. Out of all the sharks encountered only one seemed interested in the device. Here is a link to the full report. http://www.sharkspotters.org.za/wp-content/uploads/2012/06/Huveneers-et-al-2012-Shark-Shield-testing_SafeWork-SA.pdf

Here is a great site of some Great Whites tagged off Suoth Africa and every time they surface the site gets updated. So interesting to see what they are up to
http://www.sharks-ocearch.verite.com/

Brendon

[andygere]

The bait has always been there.  Sand eels, silversides, bunker, it's all in the surf zone, the estuaries, the bays.  The seal population has exploded because of the Marine Mammal Protection Act.  One of the reasons they are rafted up in huge numbers at the Cut is that the Jeeps can't get out there anymore, and the camps were stranded on what is now an island.  As the seals procreate with great efficiency, it's taken the predators a while to catch up. It looks like they are now catching up.  What is unclear is what the natural population of the seals once was, and if they ever ranged as far south as the Cape in such large numbers.  All in, no seals, no sharks.  Many seals, many sharks.  Not sure why the seals are so sacred, they won't look so cure after somebody's kid gets hit by a white shark.

[Weed]

When did the Marine Mammal Protect Act go into affect? It wasn't that long ago when the local media use to cover Andre the Seal, remember him when he took up sumer resdidence on Cape Cod. Back then it seemed like Andre was the only seal in town.