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A marine explorer in the Northern Bahamas Banks is inspecting a topsy-turvy tiger shark that is experiencing a daze-like condition recognized as induced immobility.(Image credit: Rodrigo Friscione via Getty Images)ShareShare by:
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Sharks can be fearsome hunters, although once they are upturned, multiple kinds go into a faint-like state, regarded as tonic immobility, and are as vulnerable as an insect on its carapace.
Tonic immobility is “nearly like putting a shark into a hypnotic state!” Joel Gayford, a doctoral scholar of marine ecology at James Cook University in Australia, conveyed to Live Science via electronic mail. “The creature completely ceases paddling, and the single motion it’s executing is deliberate measured breathing.”
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While experiencing tonic immobility, a shark undergoes a lessening in sensory reactivity, heart rate and blood pressure, together with analgesia, denoting a lessening in its sensitivity to pain, Abraham Miranda-Páez, a researcher at the National School of Biological Sciences in Mexico city, communicated to Live Science via email.
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Regarding the shark variants that enter tonic immobility — including great white sharks (Carcharodon carcharias), lemon sharks (Negaprion brevirostris) and gray nurse sharks (also called a sand tiger shark, or Carcharias taurus) — this stop response “can be initiated when the shark is reversed or via activating the muzzle (abode to numerous electroreceptors termed the ampullae of Lorenzini), Jillian Morris, founder of Sharks4Kids, a Florida-based non-gain organization, explained to Live Science via email.
Via putting sharks into this dormant state, scientists are enabled to execute research securely whereas alleviating pressure intended for the creature.
“We are capable of making a minor slit and inserting an acoustic tag securely and in a humane fashion, excluding the necessity for customized gear,” Morris stated. “It’s always executed incredibly rapidly, following which the shark is turned again.”
How tonic immobility aids sharks to endure
Notwithstanding, sharks didn’t build up this characteristic in order to aid scientists in taking specimens, thus what is happening?
A couple of foremost theories exist. Per a 2023 investigation in the journal Environmental Biology of Fishes, tonic immobility could be for individual safeguard, courtship or shelter from sensory overload. “The agreement amid the scientific society is that tonic immobility is a laid-back defensive reply,” stated Miranda-Páez, co-writer of the investigation.
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Within other varieties, acting as though expired can be helpful. Dice snakes and fire ants act as though they’ve turned up their toes whenever predators strike, whereas female dragonflies and European common frogs simulate their personal passing so as to keep away from sex.
Conversely, not everyone feels certain that immobilization will be efficient security for sharks. “This explanation isn’t very well-suited for sharks,” Gayford stated. “Almost all shark predators wouldn’t be discouraged via a stationary object.”
In select instances, it’s an understandable disadvantage — orcas have discerned that they can cripple sharks to overcome them and ingest their nutrient-dense livers.
Sharks go into this state while being intimate, stated Morris, who has taken note of nurse sharks mating. “The male turns the female over, and she goes into tonic immobility prior to copulation.” Nevertheless, males are affected likewise, “therefore copulation doesn’t entirely clarify the reason why this occurrence takes place,” she appended.
A 2025 investigation in the journal Reviews in Fish Biology and Fisheries intimates that tonic immobility has absolutely no intent and is only an evolutionary hangover. “We actually discovered that tonic immobility has been shed independently multiple times all through the evolutionary background of sharks and rays,” stated Gayford, a co-writer of the investigation.
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Many of the kinds that don’t hold this response probably misplaced it for a justification, Gayford stated. Commonly, undersized coral-inhabiting sharks waste vast stretches scouting for foodstuffs in tight regions, at which they can get jammed. “In the event that such varieties were to go into tonic in this circumstance, it might bear life-threatening results,” Gayford stated.
In the present day, scientists don’t possess adequate data to conclusively mention what intent tonic immobility serves. “Innumerable theories exist, without any of which are entirely realized or thoroughly backed,” Morris stated.
Editor’s note: This story was updated at 9:23 a.m. ET on July 25 to correct the title of Abraham Miranda-Páez.
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Melissa HobsonSocial Links NavigationLive Science Contributor
Melissa Hobson is a freelance author who specializes in marine science, preservation and sustainability, and particularly appreciates composing concerning the offbeat behaviors of marine creatures. Melissa has functioned in behalf of various marine conservation organizations at which she saturated up their understanding and eagerness for securing the ocean. Being a certified Rescue Diver, she gets her scuba repair where conceivable though is excessive amount of a wimp for taking a plunge within the UK these days thus inclines to stay with tropical waters. Her piece of writing has additionally manifested in National Geographic, the Guardian, the Sunday Times, New Scientist, VICE and much more.
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