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Sharks and Sleep

Started by Recusant, March 25, 2022, 04:08:48 AM

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Recusant

I was recently reading about the godwits who migrate from the Arctic to the Antarctic and back, and how they can keep flying for days by keeping only half their brain awake (uni-hemispheric slow wave sleep). The article indicates that perhaps some sharks can swim in their sleep as well.

"Biologists Just Totally Proved Wrong a Long-Standing Rumor About Sharks" | Science Alert

QuoteIt's been rumored that sharks don't sleep at all; the fact some sharks must stay on the move to facilitate their breathing has contributed to this idea.

A new study, however, finally confirms what anecdotal evidence and other research have long suggested – these animals do slumber, just as we do.

"We have provided the first physiological evidence of sleep in sharks," the team writes in their paper, led by ecophysiologist Michael Kelly from the University of Western Australia.

Two sleep phases are well known in birds and mammals, and even octopus – suggesting each stage plays an important role in our physiology, but little is known about this process in cold-blooded back-boned animals.

So the team investigated signs of sleep in the draughtsboard shark (Cephaloscyllium isabellum), which they'd previously discovered are nocturnal animals.

In a previous study, the researchers demonstrated it took greater electric stimulation for a shark to respond when the animal appeared to be resting – but they did not confirm this resting state was sleep.

Monitoring the sharks across 24 hours revealed their oxygen levels consistently decreased during these periods of restfulness, confirming those that extended beyond 5 minutes are indeed sleep.

"Not only do sleeping sharks have reduced responsiveness to stimulation, they also have lower metabolic rate," Kelly and team explains.

[. . .]

So if sleep turns out to be common across all sharks, how would the obligatory swimmers achieve it while still on the move?

Some researchers suspect it may have to do with the way these sharks control their swimming motion. A study in the 1970s found the mechanisms that oversee swimming movements in the small spiny dogfish shark (Squalus acanthias) are located in the animal's spinal cord and not the brain, so it may be possible for sharks to keep swimming while not being conscious.

[Continues . . .]

The paper is open access--

"Energy conservation characterizes sleep in sharks" | Biology Letters

QuoteAbstract:

Sharks represent the earliest group of jawed vertebrates and as such, they may provide original insight for understanding the evolution of sleep in more derived animals. Unfortunately, beyond a single behavioural investigation, very little is known about sleep in these ancient predators. As such, recordings of physiological indicators of sleep in sharks have never been reported.

Reduced energy expenditure arising from sustained restfulness and lowered metabolic rate during sleep have given rise to the hypothesis that sleep plays an important role for energy conservation. To determine whether this idea applies also to sharks, we compared metabolic rates of draughtsboard sharks (Cephaloscyllium isabellum) during periods ostensibly thought to be sleep, along with restful and actively swimming sharks across a 24 h period. We also investigated behaviours that often characterize sleep in other animals, including eye closure and postural recumbency, to establish relationships between physiology and behaviour.

Overall, lower metabolic rate and a flat body posture reflect sleep in draughtsboard sharks, whereas eye closure is a poorer indication of sleep. Our results support the idea for the conservation of energy as a function of sleep in these basal vertebrates.


"Religion is fundamentally opposed to everything I hold in veneration — courage, clear thinking, honesty, fairness, and above all, love of the truth."
— H. L. Mencken


No one

I slept with a shark once. She said it would get me off, it did.  The charges still stuck though.

Word is, it broke her heart. She went all psycho. Terrorized some quaint New England town. Had a hissy fit, and blew up on some sheriff.

Recusant

"Religion is fundamentally opposed to everything I hold in veneration — courage, clear thinking, honesty, fairness, and above all, love of the truth."
— H. L. Mencken