Tonic immobility is a natural state of paralysis that animals enter, often called animal hypnosis. Some sharks can be placed in a tonic state. The shark remains in this state of paralysis for an average of fifteen minutes before it recovers. Scientists have exploited this phenomenon to study shark behaviour. The effects of chemical shark repellent have been studied to test effectiveness and to narrow down dose sizes, concentrations, and time to awaken.
Some sharks go into tonic immobility when they are turned upside down. With tiger sharks 3–4 metres (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. Scientists believe that tonic immobility in sharks may be related to mating, because female sharks seem more responsive than males. During tonic immobility, the dorsal fin(s) straighten, and both breathing and muscle contractions become more steady and relaxed.
Great White Sharks are not so responsive as other species when tonic immobility has been attempted. In an interesting eye witness case off the coast of California, a female orca was seen holding the shark upside down to induce tonic immobility. It kept the shark still for fifteen minutes, causing it to suffocate to death. This was the first recorded eye witness case of predation on a great white shark in the wild by a species other than humans. Another case of orcas purposely inducing tonic immobility in fish has been seen with stingrays in New Zealand. In this case, the orcas turn themselves upside down before attacking, trap the stingrays in their mouths, then quickly right themselves, in turn flipping the stingray over, inducing the tonic immobility, rendering the fish helpless and an easy meal.