This according to the researchers may have more to do with light than the sleep state itself. Generally during their daytime sleep, these creatures shut their eyes but at night they preferred to keep them open more often. The scientists noted that when asleep, this position changed and they were flattening and nestling closer to the ground. As these three-foot-long fishes are ambush predators, they are usually positioned with their fins out and head up. There was a distinct change in their posture too. Sharing his view on this to Guardian, Kelly remarked: “We know that a drop in metabolism is a tell-tale sign of sleep in many, many other animals.” Resting for five minutes and more, the consumption of oxygen dropped in them, pointing to their drifting off to sleep. The scientists in order to confirm if the fishes were asleep, checked their metabolism and the bearing of seven draughtsboard sharks over 24 hours. This means that when stationary, they can push water manually over their gills to take in oxygen. This particular species which in contrast to the tiger sharks and the great whites, which need to swim constantly to keep water flowing to their gills, are buccal pumping shark species. This native to New Zealand nocturnal species was observed to be sleeping during periods of rest. The subject of this study was the draughtsboard sharks. Sharks are a particularly important group as they are the oldest living jawed vertebrates-a trait they share with us.” Kelly is an ecophysiologist at La Trobe University, Melbourne. Talking to Newsweek, Michael Kelly, an author of this study said: "Until now, sleep in sharks was completely unstudied and unknown. The details of this new study which has been published in Biology Letters, a peer-reviewed scientific journal, points out that sharks can sleep and many prefer keeping their eyes wide open while doing so. Now, a report in mentions that Australian scientists have studied and recorded a species of these fishes which live in the bottom and have been observed to sleep. It has been a long held belief that sharks don’t sleep and the reason given for this was that some of them needed to keep swimming in order to have a constant and steady supply of oxygen-rich water go through their gills. Studying the draughtsboard sharks which are native to New Zealand, scientists found out these fishes do sleep (Pic.
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