dead shark
March 8, 2012 2:03 AM   Subscribe

Here and here are examples of the remarkable tonic immobility in sharks.
posted by wilful (32 comments total) 9 users marked this as a favorite
 
If only Batman had known of this shark tickling trick!
posted by chavenet at 2:13 AM on March 8, 2012


From the "immobility" link:

Great White sharks have been shown to be not as responsive as other species whenever tonic immobility has been attempted.

Drats.

Now I wonder: Did somebody actually try to turn a Great White upside down to see if it played dead? And, more importantly: Is that person still alive and in full possession of his limbs?
posted by Skeptic at 2:14 AM on March 8, 2012 [8 favorites]


Maybe sharks just like Spanish music.
posted by arzakh at 3:02 AM on March 8, 2012 [3 favorites]


I don't get why anyone thinks it's cool that these people don't leave those animals in peace.

"Ohh it's fun and exciting to dive and see sharks close up and stuff" doesn't, to my way of thinking, cross the threshold of being important enough to violate the personal space of these animals.

To say nothing of touching them and turning them upside down against their will to test your shark repellant chemicals on them. How is this OK? Any scientific data thus obtained seems hardly useful for the sharks or in anyway of a benefit to them. Humans can easily avoid sharks and shark attacks by staying out of the shark's environment.

Go find another way to get your kicks you Jacques Cousteau wannabes. Do drugs or something useful.
posted by three blind mice at 3:13 AM on March 8, 2012


With tiger sharks 10 to 15 feet in length, tonic immobility may be achieved by placing hands lightly on the sides of the animal's snout approximate to the general area surrounding its eyes.

Yeah. Good luck with that.
posted by Joakim Ziegler at 3:27 AM on March 8, 2012 [1 favorite]


So much for the idea that sharks have to keep moving or die. Another "fact" that I know turns out to be BS.
posted by Lame_username at 3:38 AM on March 8, 2012 [1 favorite]


I don't get it. What's the evolutionary pay off for this? So they can pretend to be dead before they eat you from the toes up?
posted by angrycat at 3:45 AM on March 8, 2012


Oh wow. I really should have believed the kids on the island I do fieldwork on who were telling me they roll sharks over and rub their bellies "like puppies" and that the sharks are totally cool with it.

I thought they were having me on.
posted by lollusc at 4:30 AM on March 8, 2012 [2 favorites]


(In my defense, that was in the same conversation where they told me that "a hippopotamus" lived in the lagoon - "No, wait! Actually just the back half of a hippopotamus" and shortly before they tried to convince me that squid climb trees and eat pandanus nuts.)
posted by lollusc at 4:36 AM on March 8, 2012 [4 favorites]


To say nothing of touching them and turning them upside down against their will to test your shark repellant chemicals on them. How is this OK? Any scientific data thus obtained seems hardly useful for the sharks or in anyway of a benefit to them.

Actually, anything that keeps sharks away from humans, including repellent chemicals, is even more likely to be of benefit to the sharks than to the humans.
posted by Skeptic at 4:47 AM on March 8, 2012 [4 favorites]


Everyone knows that sharks are pathetic.
posted by ciderwoman at 4:47 AM on March 8, 2012 [1 favorite]


remarkable tonic immobility in sharks

Interesting. Achieving similar results in humans generally requires the addition of gin, quant. suff.
 
posted by Herodios at 4:54 AM on March 8, 2012 [1 favorite]


What's the evolutionary pay off for this?

I'm guessing it's more that evolution has favoured sharks who cut out the neural overhead (however small) involved in having stored behaviour patterns for occasions when the animal unexpectedly finds itself inverted, because as far as evolution knows, that doesn't happen.
posted by Segundus at 5:50 AM on March 8, 2012 [1 favorite]


I don't get why anyone thinks it's cool that these people don't leave those animals in peace.


Wait til this guy finds out what "zoos" are.
posted by allkindsoftime at 5:59 AM on March 8, 2012 [2 favorites]


...doesn't, to my way of thinking, cross the threshold of being important enough to violate the personal space of these animals.

Well then the sharks are free to go. You have to look pretty hard to find evidence of any harm here.
posted by echo target at 6:00 AM on March 8, 2012 [2 favorites]


What's the evolutionary pay off for this?

Same as for other animals that "play dead" when attacked: many predators avoid carrion because most animals dead for unseen causes are likely to carry an infectious disease.

Therefore, evolution has favoured, among predators, an instinctive repulsion for sick or dead prey, and, among their prey, an automatic reaction that exploits this instinctive repulsion. This is, I guess, why larger sharks, such as Great Whites, which are at the very top of the food pyramid, don't share this latter trait...
posted by Skeptic at 6:07 AM on March 8, 2012 [4 favorites]


About half-way into that first video, I felt like it was turning into some kind of weird shark-porn.
posted by Fizz at 6:21 AM on March 8, 2012 [6 favorites]


...doesn't, to my way of thinking, cross the threshold of being important enough to violate the personal space of these animals.

Well then the sharks are free to go. You have to look pretty hard to find evidence of any harm here.


Having contributed my jokey comment, I want to say that I'm with the visuallly impaired rodents on this one, generally, though without the anger.

When I was young, I used to think it was fun to, for example, let my dog chase squirrels, deer, etc. She was never gonna catch one anyway, so what's the harm?

The harm is that stress is a real thing, and wild animals don't need any more of it than they already have living as predators and prey in the wild.

Humans interferring with wild animals -- interrupting their activities to tag 'em for studies or whatever -- increases their stress. This could make them more likely to get sick or make a bad decision about feeding, fighting, or fleeing.

So apart from the moral hazard, I think there's always a risk of real low-level harm done to the individual animal.

I'd expect a pretty high bar for this level of interference. Moving a population in an effort to preserve an endangered species likely would clear that bar. Putting on a show for eco-tourists, likely does not.
 
posted by Herodios at 6:46 AM on March 8, 2012


What's the evolutionary pay off for this?

That's the wrong way to think about evolution and selection. It's not that this is some sort of advantage, it's just that it's never been selected against. If there was a predator that latched onto the snout of a shark to make it go immobile and then ate it (before it had reached reproductive age), there would be serious selective pressure for non-tonic sharks. But as there is no such predator, this is just a biological oddity.
posted by griffey at 7:02 AM on March 8, 2012 [6 favorites]


Anything that can help us learn to prevent the occasional 200 person shark buffet is a good thing.
posted by teekat at 7:37 AM on March 8, 2012


Humans interferring with wild animals -- interrupting their activities to tag 'em for studies or whatever -- increases their stress. This could make them more likely to get sick or make a bad decision about feeding, fighting, or fleeing.

No, see, we're helping to train them for the actual emergencies. If the squirrels don't get chased by dogs now and then they get complacent and let their guard down.
posted by rocket88 at 8:44 AM on March 8, 2012 [1 favorite]


What you all call "tonic immobility" I call "aww, widdle sharkey-warkey like'ems a cuddle, do dey?"
posted by msali at 9:03 AM on March 8, 2012 [3 favorites]


So apart from the moral hazard

Please tell me you're kidding.
posted by Dark Messiah at 11:07 AM on March 8, 2012 [1 favorite]


What's the evolutionary pay off for this?

Same as for other animals that "play dead" when attacked: many predators avoid carrion because most animals dead for unseen causes are likely to carry an infectious disease.

Therefore, evolution has favoured, among predators, an instinctive repulsion for sick or dead prey, and, among their prey, an automatic reaction that exploits this instinctive repulsion. This is, I guess, why larger sharks, such as Great Whites, which are at the very top of the food pyramid, don't share this latter trait...


Thanks, Skeptic, I'm buying that. I've always wondered why playing dead works for opossums and flat-nosed snakes, when most dogs I know will happily snap up any dead mouse they find (of any age - and I mean warm&bleeding to mummified).
posted by IAmBroom at 12:30 PM on March 8, 2012


What's the evolutionary pay off for this?

That's the wrong way to think about evolution and selection. It's not that this is some sort of advantage, it's just that it's never been selected against. If there was a predator that latched onto the snout of a shark to make it go immobile and then ate it (before it had reached reproductive age), there would be serious selective pressure for non-tonic sharks. But as there is no such predator, this is just a biological oddity.

Nope, griffey. In principle, you're correct, but that overlooks that there exists a neural mechanism by which these animals become "entranced". Planaria don't exhibit this mechanism. Goldfish don't (after a quick check).

At some point, this mechanism developed in the ancestors of these sharks. It may persist without real advantage, but nonetheless, it's interesting (and probably meaningful) to wonder why the mechanism was "allowed" to develop - did it serve a survival purpose, or is it some odd and relatively unimportant byproduct of another survival trait?
posted by IAmBroom at 12:59 PM on March 8, 2012


> Did somebody actually try to turn a Great White upside down to see if it played dead?
> And, more importantly: Is that person still alive and in full possession of his limbs?

You can do this to alligators too. I saw it demoed at a Florida alligator farm--the same one where I learned that toucans like very much to have their beaks stroked. It you hold a toucan's beak lightly by the tip and vigorously rub the top surface it will PURR LOUDLY. And become very upset when you stop and try to walk away. I found that out years ago and here I still am at this damned alligator farm rubbing this damned tyrannically demanding toucan.
posted by jfuller at 2:31 PM on March 8, 2012 [3 favorites]


At some point, this mechanism developed in the ancestors of these sharks. It may persist without real advantage, but nonetheless, it's interesting (and probably meaningful) to wonder why the mechanism was "allowed" to develop - did it serve a survival purpose, or is it some odd and relatively unimportant byproduct of another survival trait?

I'm reminded of the giraffe autopsy where they found the nerve for the larynx travelled all the way down to the heart from it's brain and back up the neck to it's final destination inches from where it originated.
posted by dibblda at 1:44 AM on March 9, 2012


Lots of dead sharks. 455 million years on the planet could end in our lifetimes.
posted by asok at 5:46 AM on March 9, 2012


Nope, griffey. In principle, you're correct, but that overlooks that there exists a neural mechanism by which these animals become "entranced".

I believe the point is that it doesn't need to be a "mechanism", but simply could be an "exploit".
posted by P.o.B. at 9:03 AM on March 9, 2012


Now that I've searched around, does anyone have a solid link that explains this? To me this looks like it could just be overstimulation. We know sharks have huge amounts of nerves running through that area, and I'm curious is there is there any real data that supports the 'playing possum' idea?
posted by P.o.B. at 11:20 AM on March 9, 2012


I had always assumed that this tonic immobility is an inadvertent result of a mating behavior where a male shark makes a female more docile to avoid injury during the mating process, but again, that is a guess.

As others have said it could just be an evolutionary artifact that was never selected for or against. I am pretty skeptical of the "playing possum" argument. There are some great vids. out there of sharks just going nuts for diseased whale carcasses etc. But maybe.

Unfortunately though, there doesn't seem to be any good data that may explain it.
posted by rosswald at 12:21 PM on March 9, 2012


"Well if you were directly next to him, how could you not just eat him?"

"Because I was inverted."
posted by Sand at 4:58 PM on March 10, 2012


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