A team of researchers from La Trobe University, the University of Western Australia and the University of Auckland have found evidence that at least one type of shark sleeps. In their article published in the journal Biology Lettersthe group describes measuring the metabolic rates of seven wild checkerboard (carpet) sharks temporarily held in a tank and what it revealed about their possible sleep patterns.
Previous research has suggested that some species of sharks sleep, while in others this seems questionable, as they must keep moving to absorb oxygen from the water. This research involved shocking resting sharks to see if they reacted as quickly as they did when active, for example. In this new effort, the researchers looked for more concrete evidence.
The team chose checkerboard sharks because they live off the coast of New Zealand where the study was conducted, and because they are known to have resting periods. They captured seven and released them into large tanks in an outdoor laboratory lit by natural light – each was fed sardines for two weeks before the experiments began and each was removed from food for 48 hours before the start of the experiment. start experiments to make sure they reach a post-absorptive state. The researchers measured the sharks’ metabolism using a submerged acrylic respirometry chamber over 24-hour periods, focusing more specifically on the shark’s oxygen levels.
They found reduced oxygen levels in all sharks during rest periods, indicating that they were sleeping. They also found that the sharks closed their eyes at rest, another indicator of sleep, and they tended to keep their bodies flat. The researchers note that such behavior is consistent with sleep in many other creatures, although they acknowledge that closing the eyes is not necessarily a sign of sleep, as other creatures have been known to sleep with their eyes closed. open, and there were occasions when the sharks in the study did not close their eyes during rest periods.
The researchers conclude that the cumulative evidence is strong for checkerboard shark sleep.
Sharks of different species hunt prey at different times to avoid each other
Michael L. Kelly et al, Energy conservation characterizes sleep in sharks, Biology Letters (2022). DOI: 10.1098/rsbl.2021.0259. royalsocietypublishing.org/doi….1098/rsbl.2021.0259
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