Scientists Confirm Sharks Do Sleep at All, Sometimes With Their Eyes Open

Sleeping sharks, with their eyes open sometimes, were discovered by scientists. The discovery adds to the unique notion that shark sleep is different than other mammals as previously thought. Nevertheless, sleep for sharks and other fish has the same purpose of energy conservation just like for mammals.

The study also confirmed from previous anecdotal evidence and research that sharks do also sleep at all. The study contradicts previous rumors that sharks do not sleep at all. In the new discovery, shark sleep was seen as a biological necessity, meaning they all sleep like other animals to sustain body functions.

Sleeping sharks pose unique characteristics since it was found most sharks shut their eyes while sleeping during daylight hours while some sleep with their eyes open. The eye patterns during shark sleep may link the common biological response to sunlight stimuli and purpose of energy conservation.

Sharks Do Sleep

(Photo : Dan Kitwood via Getty Images)

In a study published in the Biology Letters cited by Science Alert on Wednesday, March 9, biologists from Australia have confirmed previous anecdotal evidence and research that sharks also sleep like humans and other animals. This indicated sleep for sharks also serves as a biological necessity.

The scientists examined members of the draughtsboard shark (Cephaloscyllium) species. The team confirmed that the draughtsboard sharks simultaneously swim and rest to conserve oxygen as it passes through their gill. However, they also enter a state of sleep while doing this.

Meanwhile, the researchers also noticed most of the draughtsboard sharks had their eyes closed during daytime hours-a relatively similar behavior or response when humans and other mammals sleep. On the contrary, some of the sharks always had their eyes open during nighttime hours.

The patterns of eye closure and opening among the sharks during daytime and nighttime hours show that sharks also respond to the same stimuli from sunlight. This is due to the established fact that sleeping while our eyes are open to receive sunlight impedes our ability to enter into the state of sleep.

Also Read: 7 Healthy Sleeping Habits You Must Know

Previous Rumor Debunked

Over the years, unverified and subjective information on sharks in the form of a long-standing rumor that sharks are not capable of sleeping-since they need to move all the time for them to be able to breathe. However, Live Science indicated that the new study has debunked this age-old myth.

The new study stemmed from the rumors that sharks do not sleep at all. This is due to the fact it was perceived before that sharks only rest and do not enter the state of deep sleep since they continue to swim while sleeping to acquire constant oxygen through their gills, as per the Florida Museum.

The eye patterns of the sharks discovered during daytime and nighttime hours indicate that they are actually sleeping for more than five minutes in the so-called state of "restfulness." The biologists observed the sharks showed signs of decreased metabolic rate and decreased oxygen levels while sleeping.

Related Article: Cave Fish Sleep When They Please to Save Energy