The first thing is, do not try this at home. And if you do not own your own shark, do not enter your nearest shark-infested ocean to try this out. After watching the movie “Jaws”, most people would not have to be told this. However, this is a serious phenomenon which has puzzled marine biologists for quite a while. Professional divers have tried this out, and I believe most of them are still about to tell their story.
If a shark is turned upside-down or rolled into an inverted position, the shark will immediately go into a trance-like state. It is as if it has been hypnotised. This state is known as “tonic immobility”. Rolling the shark back to its original position, it immediately comes back to full consciousness. This behaviour has been witnessed in several shark species, of which there are around 200, and this includes the Great White of Jaws fame.
The obvious question is, why does this happen? There are several theories. One is that it is a defence mechanism. There are a number of creatures that play dead in the hope that their predator will ignore them and go away. The problem with this idea about sharks is that any of the predators of sharks would not ignore a dormant victim and would still attack. So, this theory does not really work.
Another theory is that it has to do with having sex. I will explain. It has been observed by some voyeurs, sorry, I mean marine biologists, that a male shark will roll a female over, which induces this condition. The shark then copulates. But this also relates to male sharks, so there is more than a little puzzlement here, too.
Lastly, it could just be a hang-up from evolution, when such a response may have been useful. Once again, we cannot be sure. However, marine biologists have been able to utilise this response. By flipping a shark over and immobilising it, they are able to quickly attach an electronic tag, so they can monitor the shark in the future. If it were not for this response, the procedure would be longer and worse for the shark.
Even so, I would not recommend you try any of this.
