Bizarre Facts: Eat, Sleep, Shark, Repeat

BRITISH COLUMBIA— A study conducted by Mike Kelly and researchers from Simon Fraser University, published by Biology Letters on March 15, uncovered the first psychological evidence that sharks take a break from the hunt to catch some zzz’s. Kelly, a comparative sleep physiologist and postdoctoral researcher at SFU’s Circadian Rhythms and Sleep Lab and Translational Neuroscience Lab, specializes in sleep among aquatic creatures, from sharks to crocodiles. 


His research found sharks produce a lower metabolic rate and recumbent body posture when inactive for longer than five minutes.


Kelly and the other researchers observed the sharks over 24-hour periods and tracked their metabolic rates and behavior during swimming, resting, and suspected sleep periods.


“The sharks showed a dramatic decrease in their metabolic rate and an obvious postural change following five minutes of inactivity, which demonstrated a distinct separation between periods of quiet wakefulness and sleep,” said Kelly in the study.


It is widely understood that animals sleep, including bony fish species. However, Kelly says the research provides the first physiological evidence of sleep among elasmobranchs, a group including sharks, rays, and skates.


Kelly earlier studied sleep behavior among crocodiles for his Honors thesis at Australia’s La Trobe University. The research found these creatures likely slept with one eye open and was later published in the Journal of Experimental Biology.


In addition to sleep research with sharks, Kelly has become fluent in the circadian rhythms and sleep behavior of many other fish species and has extended his work to include related behaviors in octopuses.


“I find the best way to overcome my sheer terror of these creatures of the deep is to get up close and personal with them,” said Kelly. “Besides, better to be around them when they’re sleeping than when they’re ready to feed!”


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