The first report of gray reef sharks resting under a reef in the Seychelles changed our understanding of how they breathe (they don't need constant swimming to stay alive) and reopened scientific research on sleeping sharks.
Predators are always in motion. Sleepless in our oceans. If this is your impression of sharks, you're not alone. It makes sense: sharks have to swim to breathe (or so we're told). Sleep and breathing in sharks are interconnected, and while all sharks breathe through their gills, they have two ways of expelling oxygen-rich seawater through their gills.
Some sharks, known as "forced impact rebreathers," "blast" oxygen-rich water onto their gills and need to be constantly moving to do so. Other species of sharks, known as "buccal pumps," actively pump seawater over their gills when at rest.
Evidence of shark resting: a new perspective
Science today tells us that sharks can stand still - and some believe they are sleeping. But so far there is no conclusive evidence that their respirators engage in sleep behavior. Scientists hypothesize that they don't sleep at all, or that they sleep with half their brain (like sperm whales and bottlenose dolphins), or that they sleep facing the ocean currents.
A new paper published this month in the Journal of Fish Biology, entitled "Observations of resting behavior of gray reef sharks" (Observations of resting behavior of gray reef sharks Carcharhinusamblyrhynchos (Bleeker, 1856)), subverts our understanding of a forced impact ventilator. The gray reef shark is an endangered coral reef-dwelling animal that is the poster child for sharks that move to breathe.
Dr Robert Bullock, Director of Research at Save the Sea Foundation's Daros Research Center (SOSF-DRC) in Seychelles, said: "During routine dive surveys near Daros, we found gray reef sharks resting under coral reef ledges. We did not believe they were able to do this. Gray reef sharks have always been considered a collision-breathing species and cannot rest, so finding these gray reef sharks resting changes our basic understanding of them."
Researchers found gray reef sharks resting alone and in groups at various locations near the Seychelles. Throughout the process, the shark appears oblivious to the observer. This is an important observation: Scientists believe that an increase in arousal threshold is a sign of sleep, not just rest.
The sharks were motionless, with only their jaws moving, suggesting that these collision-ventilating sharks can switch to buccal pump behavior. Since there is almost no current at these sites and the sharks face in all directions while resting, the idea that the only way they can rest is by facing the current does not seem to hold true for gray reef sharks.
Craig Foster, founder of the Ocean Change Project, is one of the divers and an author of the paper. He said: "It is a very special feeling to watch the sharks open their sleepy eyes at a depth of 25 meters, moving carefully so as not to wake up these peaceful beauties."
Impact and future research
"I like things that challenge our current thinking, and I have always thought that gray reef sharks are a clear example of a species that needs to swim and breathe. This is clearly not the case!" Dr. James Lea, CEO of Save the Sea Foundation, is enthusiastic about the predictions of this paper. "This raises all kinds of other questions," he said. How do they cope? How long does it last? How often? We still have a lot to learn, and that excites me."
If gray reef sharks can switch breathing patterns and rest, there's a lot more to discover about similar sharks. Dr Lea explained: "This is key to understanding how they use their environment and how that changes as environmental conditions change. How important is rest, or possibly sleep, to sharks? If environmental conditions change, such as oxygen levels rising or falling due to changes in climate, what will be the impact on sharks if they are unable to get rest?"
Remind us of our connection with nature
The authors agree that the discovery also says something about our own relationship with the natural world. I hope these findings serve as a reminder of how much we still don’t know, and how exciting that is. Science is about being wrong all the time. That's okay," Dr. Bullock reflected. "Mr. Foster believes that what we know about wild sharks is critical to their conservation. Understanding how our shark relatives sleep brings us closer to their fascinating world, and awakens from our own slumber to the realization that we cannot live without these magnificent sea creatures. "
Compiled source: "target="_blank">ScitechDaily