Rethinking Shark Breathing: Surprising Resting Behavior of Gray Reef Sharks Revealed

The first report of gray reef sharks resting under a reef in the Seychelles changes our understanding of how they breathe (they don’t need to constantly swim to stay alive) and reopens the door to sleeping shark science.

Predators never stop. Our waters never sleep. If this is how you feel about sharks, you’re not alone. There’s a good reason for this: Sharks have to swim to breathe (or so we’re told). The science of how sharks sleep and breathe is interconnected, and while all sharks breathe through their gills, they have two ways of moving oxygen-rich seawater over their gills.

Some sharks, known as obligate collision ventilators, “rush” oxygen-rich water to their gills and need to be constantly moving to do so.other kindCalled the buccal pump, it actively pumps seawater through the gills when at rest.

Evidence of shark resting: a new perspective

Science today tells us that sharks can stand still—and there are some suggestions that they sleep. But there is no conclusive evidence that ram respirators have sleep behavior. Scientists speculate that they don’t sleep at all, sleep with half their brains (like sperm whales and bottlenose dolphins), or sleep facing the ocean currents.

A new paper, “Keep swimming? Observations on the resting behavior of gray reef sharks” bluntnose shark (Bleeker, 1856),” published this month in Journal of Fish Biology Subverting our understanding of specialized ram respirators. The gray reef shark is an endangered coral reef dweller of the family Carcharhinidae and a prime example of a shark that breathes through movement.

The first evidence of gray reef sharks resting under a reef in the Seychelles.Photo credit: Photo by Craig Foster | © Save Our Oceans Foundation

“During a routine survey dive around Daros, we spotted gray reef sharks resting under a coral reef ledge,” said Robert Block, Research Director of the Save Our Seas Daros Research Center (SOSF-DRC) in Seychelles. Bullock said. “This is not something we thought they were capable of. Gray reef sharks are thought to be a ram-breathing species that cannot rest, so finding these resting sharks turns our basic understanding of them upside down.”

Sharks at rest: a surprising discovery

Researchers encountered gray reef sharks resting alone and in groups at various locations around the Seychelles. Throughout the entire process, the shark seemed blissfully unaware of the observer’s presence. This is a key observation: Scientists believe that an increase in arousal threshold is seen as a sign of sleep, not just rest.

The shark remained motionless except for jaw movements, suggesting that these ram-ventilating sharks can switch to buccal pump behavior. Since there is little to no current at these sites and the sharks face in all directions while resting, the only way for gray reef sharks to rest is to face the current and there does not appear to be much water.

Craig Foster, founder of the SeaChange project, is a diver and one of the authors of the paper. “This is a very special feeling,” he said, “standing on tiptoes 25 meters deep, looking at the open eyes of sleeping sharks, moving carefully so as not to wake up these peaceful beauties. biology.”

Impact and future research

“I like things that challenge our current thinking, and I’ve always thought of gray reef sharks as a clear example of a species that needs to swim to breathe. Clearly not from this discovery!” Dr. James Lee, CEO of the Save Our Seas Foundation, commented on the paper What is foreshadowed is passionate. “This raises all kinds of other questions,” he declared. “How do they respond? How long does it take to do… how often? We still have a lot to learn, and to me that’s exciting.”

If gray reef sharks can change their breathing patterns and rest, there’s much more to discover about similar sharks. “Understanding how they use their environment and how environmental conditions change is key,” Dr. Lea explains. “How important is this rest, or possible sleep, to sharks? What would be the impact on them if conditions change, such as climate change causing oxygen levels to rise or fall, and they don’t get that rest?”

Remind us of our connection with nature

The authors agree that the discovery also says a lot about our relationship with the natural world. “I hope these findings serve as a reminder of how much we don’t know, and how exciting that is. Science makes a lot of mistakes. And that’s okay,” Dr. Block reflects. Mr Foster believes our understanding of wildlife is vital to conservation. “Understanding how our shark family sleeps is a way to get closer to their fascinating world, and to wake up from our own slumber and realize that we cannot survive without these magnificent sea creatures,” he said.

Reference: “Keep swimming? Observations of resting behavior of gray reef sharks” bluntnose shark (Bleeker, 1856)” Author: Robert W. Bullock, Craig Foster and James SE Lea, November 20, 2023 Journal of Fish Biology.
DOI: 10.1111/jfb.15623