Sharks & Tonic Immobility

We investigate the tonic immobility phenomenon, whereby a shark falls into a hypnotic trance if it is turned upside down. Although useful for scientific research, is induced shark tonic immobility being abused?

Tonic immobility, by definition, is a state of apparent paralysis that animals enter usually in response to a threat, although it has also been correlated with mating in sharks. Virtually nothing is known about its underlying neurological and physiological processes in sharks. When inducing TI, the shark is flipped straight on its back and held in that position until it is turned back. Due to this knowledge, a lot of scientists have used it to their advantage, particularly for tag insertion and measurements of the sharks. The sharks do not move or try to get away. They stay in this catatonic state until they are inverted.

While it is okay in my personal and professional opinion to place sharks in TI for the sake of scientific research or for hook removals, it is not okay to place a shark in TI so that people (paying customers or individuals) can see how “cool” it looks or so that they can take photos of it being done. The sharks do not benefit from interactions like this and should not be subjected to such pointless stressful situations. As divers, it is our duty to dive responsibly and always be respectful of marine animals. Recently, there have been quite a few viral videos of people harassing (poking, prodding, riding, hugging, grabbing, etc.) sharks while diving because they saw it being done by other “professional” divers. Several videos have also surfaced and others have been around for a long time of dive operators placing sharks under TI so that their customers can take photos with the animals. This is not okay.

TI has been beneficial for scientists to have the animals in this state while still being able to keep them in the water. A few scientific studies have been conducted and the findings suggested that TI was correlated with a “…significant depression in blood pressure and heart rate…” (Davie, et al.) in black tip reef sharks. In another study conducted on juvenile lemon sharks, findings mentioned that TI “… induced a short term reduction in ventilatory efficiency…” and “animals maintained in TI were significantly hyperglycaemic compared to those that were not” (Brooks, et al.). Not a lot of research has been done on the effects of TI on sharks, but one thing can definitely be stated and that is that proper care should always be taken when using the technique during research, tagging, measurement or hook removal (to name a few positives) on the animals.

With each person trying to upstage the next, we are beginning to lose sight of why diving was a passion in the first place. It is possible to enjoy wildlife without harassing it; poking, prodding, riding and hugging are all forms of wildlife harassment. What we all need to understand is that just because we can do something, does not mean we should. As a species, we have slowly begun to forget what it is to respect other living creatures.

Sharks are majestic, mysterious and marvellous animals that should not be feared, but lack of fear should also not be synonymous with a lack of respect. When diving with sharks, we should always proceed with caution, respect and, ultimately, keep our hands to ourselves. Diving is a wonderful activity and so many people partake in it so often and seeing sharks underwater is always an incredible experience. Nothing beats being able to see sharks in the wild, behaving naturally; sharks do not need gimmicks to be one of the coolest animals on this planet, they do that all on their own.



Brooks, Edward J., Katherine A. Sloman, Stephanie Liss, Laila Hassan-Hassanein, Andy J. Danylchuk, Steven J. Cooke, John W. Mandelman, Gregory B. Skomal, David W. Sims, and Cory D. Suski. "The Stress Physiology of Extended Duration Tonic Immobility in the Juvenile Lemon Shark, Negaprion Brevirostris (Poey 1868)."Journal of Experimental Marine Biology and Ecology 409.1-2 (2011): 351-60. Print.

Davie, Peter S., Craig E. Franklin, and Gordon C. Grigg. "Blood Pressure and Heart Rate during Tonic Immobility in the Black Tipped Reef Shark,Carcharhinus Melanoptera."Fish Physiology and Biochemistry 12.2 (1993): 95-100. Print.

Henningsen, A.D., (1994). Tonic immobility in 12 elasmobranchs - use as an aid in captive husbandry. Zoo Biology, 13: 325-332