The creatures that live in the depths of the ocean hold endless mysteries that scientists have gradually revealed. One of the questions that has most intrigued marine life scholars is how sharks manage to fall asleep. For decades it was thought that sharks never slept, since they cannot stop moving, because if they did, they would not be able to take advantage of the oxygen in the water through their gills. But new research has revealed this ancient secret and the results are extremely interesting.
Ecophysiologists from the University of , delved into the analysis of metabolic levels or, in other words, how much energy shot sharks (Cephaloscyllium isabellum) burn. The goal was to discover how these sharks expend energy and then recover it, a long-standing mystery since it was thought that oceanic predators never sleep.
Eyes wide open
Contrary to what was previously believed, the research revealed that sharks do sleep, but they do so in a peculiar way; Ocean predators manage to reconcile by keeping both eyes wide open. It turned out that these animals frequently enter a state of rest to conserve their energy and when this rest exceeds five minutes, scientists call it sleep.
“We have provided the first physiological evidence of sleep in sharks,” the authors write in their study. They also describe that these large marine animals enter a state of rest at different intervals throughout the 24 hours of the day, in order to conserve their energy and continue swimming.
The discovery that sharks do sleep required an analysis of the energy burned throughout the day, in this case by sharks called Cephaloscyllium isabellum. Thanks to this, they realized that sharks do not sleep like most living beings.
Unlike most animals that look for a dark, safe place to fall asleep, sharks temporarily ‘deactivate’ to conserve the energy provided by food. These short breaks can last more than 5 minutes and are not limited to the night, but are done throughout the 24 hours of the day.
A ‘fossil’ of behavior
Michael Kelly, principal investigator of the study, noticed that only one region of the sharks’ brain is deactivated when they enter a resting state, which is why they manage to do so with their eyes wide open. He also explains that this is probably why it was thought that sharks do not sleep, as they only remain static for a few minutes and then continue on their way.
These types of marine animals cannot stay still for long, otherwise their gills do not take advantage of the oxygen available in movement. But apparently a few minutes don’t make a difference in their bodies and they can easily deal with it.
Kelly and his team have said that although the research focused on draft sharks, it is likely that this behavior also applies to other species of marine predators. And they also believe that their dream form could represent a ‘fossil’, as it could shed light on how the most complex early organisms managed to store energy.
References: Kelly, M. (2022). Energy conservation characterizes sleep in sharks. Biology Letters. DOI