March 2014.
Already in 1646, the researcher expert in animal hypnosis, Giman, considered tonic immobility in animals as a response enhanced by an induced fear and that reduces the individual's capacity to respond to the external stimulation that provokes that fear.
For the French biologist Georges Pasteur, "it is a form of self-mimicry" of camouflage or mimicry trying to pass as dead.
Okay, we all agree on the same thing: tonic immobility is recognized as a natural state of paralysis that many animals suffer when faced with a situation of stress, danger or threat.
But... does the animal provoke it voluntarily in response to a stimulus or not?
We could differentiate between two types of tonic immobility: one generated by the individual itself and the other induced by an external agent.
"I play dead"
In some groups of invertebrates and vertebrates, it has been seen that they are the ones who provoke this cataleptic state of paralysis as a defense against an attacker: beetles, crickets, wasps, birds, snakes, ...
There are also "smarter" ones that provoke this "pseudo paralysis" not to avoid being hunted but to become stealthy hunters. This is the case of predatory fish such as Haplochromis livingstonii, which lies on the bottom sediment pretending to be sick or dead (it even changes its coloration) and, when a scavenger approaches, it straightens up and turns from an easy meal to a specialized hunter.
Nature also takes advantage of tonic immobility as a tool for greater success in the mating process. This is the case with some female sharks, among other animals.
"They provoke me."
In New Zealand and California, it has been observed how killer whales beat sharks and rays into an inverted position, thus inducing tonic immobility, in order to attack them more easily and be able to devour them.
There is also the case of scientifically provoked tonic immobility, that is, provoked by researchers as a working tool. In this case, the researcher acts as an attacker and places the species to be studied in a certain position (generating pain, as in the case of rodents; laying them on their belly, in bovines; placing them on their sides, in hens; turning them over, as in the case of many birds...), the individual feels threatened and "plays dead":
It is a technique used for: transportation, measurements, veterinary treatments ...
HYPNOTIZING SHARKS
But the immobility tonic that almost all divers know is the one that has shown us a wonderful video of Cristina Zenato with gray reef sharks.
Karlos Simón wanted to follow in Zenato's footsteps but going a little further: with tiger sharks.
How a tiger shark could be paralyzed
In the case of sharks in general, tonic immobility is achieved by placing them in an inverted position, but it doesn't work with all species. Lemon sharks, blacktip sharks, nurse sharks, blue sharks, gray sharks, ... are some of them. But in the case of tiger sharks between 3 and 5 meters in length, this did not seem very easy to do.
Scientific research has induced the tonic immobility of sharks with electric shocks and has shown that the animal suffers a disorientation in its sensory system that helps to generate the state of paralysis without exposure to an apparently significant stress.
Evidently the idea was not to shock them, but André Hartman (South African shark expert) discovered that touching the white sharks' snouts left them in a hypnotic state for a few seconds.
And thinking about the sense that sharks have related to the ampullae of Lorenzini, as special sensory organs that detect electromagnetic fields, we thought that stroking their snouts, in the same way that André and Cristina Zenato did, could alter that sense right in the area where the largest number of these ampullae are distributed.
It initially doesn't seem complicated, and even more so with Karlos Simón's experience with these sharks. You only (only?) have to place your hands on the perimeter surrounding its mouth and eyes and stroke it calmly until it becomes totally quiet...
My experience in tonic immobility with tigers (March 2014)
One of the objectives of last March's trip to Tiger Beach (Bahamas) was this, to try the tonic immobility with the technique used by Cristina with the grays or André with the whites, applied to tiger sharks.
Said and done. My film crew (Teresa Migoya and Mateo Silvente) and I dived in "Fish Tale", a dive very close to Tiger Beach, in search of tiger sharks.
We positioned ourselves with the bait box in the middle of the sandy area and after a few minutes the tigers began to arrive. Two, three and in some moments even four surrounded us. Once again it was demonstrated that this species of shark is curious. The dive was promising...
I decided to go for the one that apparently lent itself more to direct contact. It entered the box without looking at it, trying to bite it and I saw in this situation the moment to act. I held its snout with my left hand while with my right hand I caressed the area of its mouth, eyes and spiracles, where the Lorenzini's blisters are located.
Nothing, the shark would not stay still, it was impossible to stop him, let alone immobilize him. I tried several times, but there was no way to do it.
Considering the "success" obtained, I tried to include another step to the technique: closing the shark's mouth with my hands to try to turn him over. This technique is used with smaller sharks, but I didn't know if it would be feasible with tiger sharks...
The same "playful" shark unhesitatingly reentered the bait box. It opened its huge mouth trying to bite it. In one of his casts, I decided to close it with my hands and tried to flip him over (very risky maneuver especially for the hand underneath). First attempt failed! The tiger shark, because it was a female, weighing almost a ton, called from that day on -Teresa-, did not let me turn her over to immobilize her.
Second attempt. This time my "diving companion" did not stop chewing non-stop on the box. I managed to close her mouth with my hands, I started to turn her on herself and... Success! She closed her eyes with the nictitating membrane (or third eyelid, with which they protect the eyeball when closing it), she relaxed, her breathing slowed down and she let herself go. At that moment I achieved her immobility and was able to lift her until she was perpendicular to the fundus.
After a few seconds (which felt like an eternity) the shark reacted, began to shake its body and returned to its normal position without any damage.
Mission completed! The prevailing theory that in sharks the inverted state causes a physiological imbalance and the consequent tonic immobility, is also demonstrated in the case of tiger sharks.
Why to do these performances with sharks?
And after all this, what do you think? Is the tiger shark afraid of Karlos Simón and plays dead or is it the diver who is managing to "hypnotize" the "man-eater"?
Joking aside, the truth is that Karlos has managed to immobilize it for a few seconds, but the objective is not to play with the shark and caress it, but, on the one hand, to demonstrate once again that sharks are not "man-eaters" and that you can interact with them; and on the other hand, that the tonic immobility can be a great working tool for research on these animals in their natural environment, without the need to generate the stress that may involve taking them out of the water, their natural environment.
