Tonic immobility is a phenomenon in which some animals experience paralysis and loss of muscle tone when presented with certain stimuli. This state has been reported to occur in insects, reptiles, birds, amphibians, mammals and fish.
Tonic Immobility in Sharks and Rays
Sharks and rays enter a trance-like state when their sensory pores on the nose are stimulated. This phenomenon is known as tonic immobility, or “trance.” Tonic immobility can occur naturally in these animals; however, it’s mostly induced by humans. This makes them more manageable during research projects involving sharks and rays of various species. Even though tonic immobility does not occur in all species of sharks, it still affects most types. In the Great White shark, its dorsal fin straightens and breathing slows down as well as muscle contractions become lax. For many animals that can experience this state, it is a survival strategy because looking dead to predators is useful sometimes for tricking them into letting their guard done long enough or altogether if they aren’t being too observant.
When researchers handle sharks, they often use tonic immobility to subdue them. Many scientists think that this is what occurs when the shark enters a trance-like state of relaxation and becomes deeply rhythmic in its breathing patterns. When gently turned on its back, its thought enters into this stage as an act of disorientation which relaxes the muscles and induces deep breathing rhythms without causing injury or struggle. Once released from these restraints, however, the shark will snap out of this daze within moments.
Scientists are still unsure why sharks enter tonic immobility. Some suggest it may be a defence strategy while others think that is related to mating behaviour, but nobody knows for sure at this point in time.
So, why would tonic immobility be useful for sharks?
Perhaps it’s a defence strategy. Playing dead could deter potential predators! But some shark species that enter this state are apex predators and don’t have many natural enemies. Some scientists suggest they might do it to mate but nobody really knows the answer yet – we’ve still got a lot more research to do on these animals! Sharks can enter tonic immobility in less than a minute. They remain like this for up to 15 minutes if undisturbed, which is useful when testing chemical shark repellents that are meant to keep sharks away from humans without harming the sharks themselves.
There is evidence to suggest that orcas use tonic immobility as a hunting technique. For example, in 1997 an Orca near the Farallon Islands held a Great White Shark upside down for 15 minutes and suffocated it because of paralysis caused by this behaviour. This same observation was made again in 2000 with stingrays. In New Zealand Orcas similarly prey on stingrays using Tonic Immobility: they turn themselves upside-down first then flip their prey up-side-down which paralyzes them before eating them.
Tonic immobility is a phenomenon in which some animals experience paralysis and loss of muscle tone when presented with certain stimuli. This state has been reported to occur in insects, reptiles, birds, amphibians, mammals and fish. Sharks and rays enter a trance-like state when their sensory pores on the nose are stimulated. Tonic immobility can occur naturally or be induced by humans as a means of subduing sharks during research projects involving different species for chemical shark repellents that keep them away from humans without harming the animal itself. In fact, there’s evidence suggesting orcas use tonic immobility as a hunting technique too! Scientists still don’t know why this occurs but it could be due to defence strategy or mating behaviour–only more research will tell!