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How do diving marine mammals avoid decompression sickness?

How do diving marine mammals avoid decompression sickness?


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How do marine mammals, whose very survival depends on regular diving, manage to avoid decompression sickness or "the bends?" Do they, indeed, avoid it?


I think I got the answer…

The primary anatomical adaptations for pressure of a deep-diving mammal such as the sperm whale center on air-containing spaces and the prevention of tissue barotrauma. Air cavities, when present, are lined with venous plexuses, which are thought to fill at depth, obliterate the air space, and prevent "the squeeze." The lungs collapse, which prevents lung rupture and (important with regard to physiology) blocks gas exchange in the lung. Lack of nitrogen absorption at depth prevents the development of nitrogen narcosis and decompression sickness.

Source: Scientific American


I concur with @souvik.bhattacharya but I wish to elaborate on it. The lung collapse indeed stops gas exchange in marine mammals by keeping the air away from the lung tissue that normally exchanges O2, CO2 and N2. Build up of N2 results in the bends after the pressure drops when re-surfacing (McDonald & Ponganis, 2012). However, a study by Hooker et al. (2012) showed that beached whales, dolphins and seals did show signs of bubble formation in the internal organs, which was linked to exposure to noise and sonar, or other factors such as cold water that may disrupt the functionality of preventive measures such as the lung collapse. So to get back to your question - Yes they avoid it by lung collapse, but under certain conditions this mechanism may fail.


Study examines how diving marine mammals manage decompression

Any diver returning from ocean depths knows about the hazard of decompression sickness (DCS) or "the bends." As the diver ascends and the ocean pressure decreases, gases that were absorbed by the body during the dive, come out of solution and, if the ascent is too rapid, can cause bubbles to form in the body. DCS causes many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. But how do marine mammals, whose very survival depends on regular diving, manage to avoid DCS? Do they, indeed, avoid it?

In April 2010, the Woods Hole Oceanographic Institution's Marine Mammal Center (MMC) invited the world's experts in human diving and marine-mammal diving physiology to convene for a three-day workshop to discuss the issue of how marine mammals manage gas under pressure. Twenty-eight researchers discussed and debated the current state of knowledge on diving marine mammal gas kinetics -- the rates of the change in the concentration of gases in their bodies.

The workshop resulted in a paper, "Deadly diving? Physiological and behavioural management of decompression stress in diving mammals," which was published Dec. 21, 2011, online in the Proceedings of the Royal Society B.

"Until recently the dogma was that marine mammals have anatomical and physiological and behavioral adaptations to make the bends not a problem," said MMC Director Michael Moore. "There is no evidence that marine mammals get the bends routinely, but a look at the most recent studies suggest that they are actively avoiding rather than simply not having issues with decompression."

Researchers began to question the conventional wisdom after examining beaked whales that had stranded on the Canary Islands in 2002. A necropsy of those animals turned up evidence of damage from gas bubbles. The animals had stranded after exposure to sonar from nearby naval exercises. This led scientists to think that diving marine mammals might deal with the presence of nitrogen bubbles more frequently than previously thought, and that the animals' response strategies might involve physiological trade-offs depending on situational variables. In other words, the animals likely manage their nitrogen load and probably have greater variation in their blood nitrogen levels than previously believed.

Because the animals spend so much time below the ocean's surface, understanding the behavior of diving marine mammals is quite challenging. The use of innovative technology is helping to advance the science. At WHOI, scientists have used a CT scanner to examine marine mammal cadavers at different pressures to better understand the behavior of gases in the lungs and "get some idea at what depth the anatomy is shut off from further pressure-kinetics issues," Moore said. For other studies, Moore and his colleagues were able to acquire a portable veterinary ultrasound unit to look at the presence or absence of gas in live, stranded dolphins.

There's still a lot to be learned, including whether live animals have circulating bubbles in their systems that they are managing. If they do, says Moore, noise impacts and other stressors that push the animal from a normal management situation to an abnormal situation become more of a concern. "When a human diver has some bubble issues, what will they do? They will either climb into a recompression chamber so that they can recompress and then come back more slowly, or they'll just grab another tank and go back down for a while and . . . and just let things sort themselves out. What does a dolphin do normally when it's surfaced? The next things to do is to dive, and the one place you can't do that is in shallow water or most particularly if you are beached."


How Sea Lions Avoid Decompression Sickness

Decompression sickness, or the bends, occurs when a scuba diver breathes in nitrogen at depth and ascends too rapidly for the nitrogen to dissipate. The nitrogen bubbles in the blood stream, causing pain or even death. Scientists have long wondered how marine mammals, who often dive to depths of hundreds of feet, avoid decompression sickness. They have since learned that marine mammals rarely suffer from decompression sickness, but that they can in certain circumstances.

A 2012 study tracked a sea lion during 48 dives. During each dive the sea lion collapsed its lungs at around 731 feet deep and continued to about 994 feet deep before resurfacing. The ability to collapse the lungs is part of a diving response which is a reflex common to all vertebrates, including humans. It is more developed in diving sea mammals such as sea lions. This allows them to automatically slow their heart rate, which decreases the need for oxygen.

Early studies found that the heart rate could decrease from 150 beats per minute to only 10 beats per minute. Blood is shunted from the muscles, which use more oxygen, to the brain and other important organs. Sea lions also have more myoglobin and hemoglobin in their blood, which helps store needed oxygen. The ability to collapse their lungs due to their unique lung structure forces air into the upper airways, where it cannot enter the bloodstream. If the air can&rsquot enter the bloodstream, it can&rsquot absorb nitrogen at depth. This also gives the sea lion an air reservoir to use on the trip back to the surface.

A study by the Royal Society study theorized that diving mammals may occasionally push the limits of diving time and depth, allowing a tolerance for increased nitrogen levels. The physiological adaptations to deep diving are a combination of automatic and controlled. It is important to remember that sea lions may have to dive deeper or stay down longer when foraging for food. Likewise, avoiding predators may require a very quick ascent and the extreme pressure changes that go with it.

Signs of decompression sickness, including bubbles, have been found in marine mammals caught in fishing nets where death occurred at around 229 to 328 feet. Scientists could not determine if the nitrogen levels increased from struggling against the net or were a normal finding for that animal at that depth. Ultrasound imaging of live-stranded dolphins found nitrogen bubbles in the kidneys and liver. The animals were tagged, and later found to have survived despite the presence of bubbles.

Interestingly, the study of sea lions and other dead mammals has found at least one cause of death from decompression sickness: extremely loud noise. Military maneuvers involving sonar have resulted in the later finding of carcasses in which death was caused by decompression sickness. It is unclear whether the sonar disoriented the animals or caused them to surface quicker than usual. More studies will be needed to further explore the physiological protections and responses that sea lions have toward decompression sickness. Understanding them can be helpful in applying techniques for human divers to avoid decompression sickness and minimize its side effects.


How do marine mammals avoid the bends?

IMAGE: Deep-diving whales and other marine mammals like these Pacific white-sided dolphins can get the bends--the same painful and potentially life-threatening decompression sickness that strikes scuba divers who surface too quickly. view more

Credit: Photo by Lance Wills, © Woods Hole Oceanographic Institution

Deep-diving whales and other marine mammals can get the bends--the same painful and potentially life-threatening decompression sickness that strikes scuba divers who surface too quickly. A new study offers a hypothesis of how marine mammals generally avoid getting the bends and how they can succumb under stressful conditions.

The key is the unusual lung architecture of whales, dolphins and porpoises (and possibly other breath-holding diving vertebrates), which creates two different pulmonary regions under deep-sea pressure, say researchers at the Woods Hole Oceanographic Institution (WHOI) and the Fundacion Oceanografic in Spain. Their study was published April 25, 2018, in the journal Proceedings of the Royal Society B.

"How some marine mammals and turtles can repeatedly dive as deep and as long as they do has perplexed scientists for a very long time," says Michael Moore, director of the Marine Mammal Center at WHOI and co-author of the study. "This paper opens a window through which we can take a new perspective on the question."

When air-breathing mammals dive to high-pressure depths, their lungs compress. That collapses their alveoli--the tiny sacs at the end of the airways where gas exchange occurs. Nitrogen bubbles build up in the animals' bloodstream and tissue. If they ascend slowly, the nitrogen can return to the lungs and be exhaled. But if they ascend too fast, the nitrogen bubbles don't have time to diffuse back into the lungs. Under less pressure at shallower depths, the nitrogen bubbles expand in the bloodstream and tissue, causing pain and damage.

Marine mammals' chest structure allows their lungs to compress. Scientists have assumed that this passive compression was marine mammals' main adaptation to avoid taking up excessive nitrogen at depth and getting the bends.

In their study, the researchers took CT images of a deceased dolphin, seal, and a domestic pig pressurized in a hyperbaric chamber. The team was able to see how the marine mammals' lung architecture creates two pulmonary regions: one air-filled and the other collapsed. The researchers believe that blood flows mainly through the collapsed region of the lungs. That causes what is called a ventilation-perfusion mismatch, which allows some oxygen and carbon dioxide to be absorbed by the animal's bloodstream, while minimizing or preventing the exchange of nitrogen. This is possible because each gas has a different solubility in the blood. The terrestrial pig did not show that structural adaptation.

This mechanism would protect cetaceans from taking up excessive amounts of nitrogen and thus minimize risk of the bends, says lead author Daniel García-Parraga of the Fundacion Oceanografic.

However, he said, "Excessive stress, as may occur during exposure to human-made sound, may cause the system to fail and increase blood to flow to the air-filled regions. This would enhance gas exchange, and nitrogen would increase in the blood and tissues as the pressure decreases during ascent."

Scientists once thought that diving marine mammals were immune from decompression sickness, but a 2002 stranding event linked to navy sonar exercises revealed that 14 whales that died after beaching off the Canary Islands had gas bubbles in their tissues--a sign of the bends. The researchers say the paper's findings could support previous implications of decompression sickness in some cetacean mass strandings associated with navy sonar exercises.

The team says further research will require the development of tools to analyze how lung blood flow and ventilation patterns change with various stressors during diving.

This work was supported by funding from the Fundacion Oceanografic and the Office of Naval Research.

The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment. For more information, please visit http://www. whoi. edu.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.


Study examines how diving marine mammals manage decompression

Any diver returning from ocean depths knows about the hazard of decompression sickness (DCS) or "the bends." As the diver ascends and the ocean pressure decreases, gases that were absorbed by the body during the dive, come out of solution and, if the ascent is too rapid, can cause bubbles to form in the body. DCS causes many symptoms, and its effects may vary from joint pain and rashes to paralysis and death.

But how do marine mammals, whose very survival depends on regular diving, manage to avoid DCS? Do they, indeed, avoid it?

In April 2010, the Woods Hole Oceanographic Institution's Marine Mammal Center (MMC) invited the world's experts in human diving and marine-mammal diving physiology to convene for a three-day workshop to discuss the issue of how marine mammals manage gas under pressure. Twenty-eight researchers discussed and debated the current state of knowledge on diving marine mammal gas kinetics—the rates of the change in the concentration of gases in their bodies.

The workshop resulted in a paper, "Deadly diving? Physiological and behavioural management of decompression stress in diving mammals," which was published Dec. 21, 2011, online in the Proceedings of the Royal Society B.

"Until recently the dogma was that marine mammals have anatomical and physiological and behavioral adaptations to make the bends not a problem," said MMC Director Michael Moore. "There is no evidence that marine mammals get the bends routinely, but a look at the most recent studies suggest that they are actively avoiding rather than simply not having issues with decompression."

Researchers began to question the conventional wisdom after examining beaked whales that had stranded on the Canary Islands in 2002. A necropsy of those animals turned up evidence of damage from gas bubbles. The animals had stranded after exposure to sonar from nearby naval exercises. This led scientists to think that diving marine mammals might deal with the presence of nitrogen bubbles more frequently than previously thought, and that the animals' response strategies might involve physiological trade-offs depending on situational variables. In other words, the animals likely manage their nitrogen load and probably have greater variation in their blood nitrogen levels than previously believed.

Because the animals spend so much time below the ocean's surface, understanding the behavior of diving marine mammals is quite challenging. The use of innovative technology is helping to advance the science. At WHOI, scientists have used a CT scanner to examine marine mammal cadavers at different pressures to better understand the behavior of gases in the lungs and "get some idea at what depth the anatomy is shut off from further pressure-kinetics issues," Moore said. For other studies, Moore and his colleagues were able to acquire a portable veterinary ultrasound unit to look at the presence or absence of gas in live, stranded dolphins.

There's still a lot to be learned, including whether live animals have circulating bubbles in their systems that they are managing. If they do, says Moore, noise impacts and other stressors that push the animal from a normal management situation to an abnormal situation become more of a concern. "When a human diver has some bubble issues, what will they do? They will either climb into a recompression chamber so that they can recompress and then come back more slowly, or they'll just grab another tank and go back down for a while and . . . and just let things sort themselves out. What does a dolphin do normally when it's surfaced? The next things to do is to dive, and the one place you can't do that is in shallow water or most particularly if you are beached."


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Physics of the ‘Bends’: New Study Helps Explain Decompression Sickness (June 28, 2010) — As you go about your day-to-day activities, tiny bubbles of nitrogen come and go inside your tissues. This is not a problem unless you happen to experience large changes in pressure, as scuba divers … > read more How Whales And Other Marine Mammals React To Sonar (Aug. 9, 2008) — Marine biologists have just completed a pioneering research effort in Hawaii to measure the biology and behavior of some of the most poorly understood whales on Earth. During the study, for the first … > read more How Diving Leatherback Turtles Regulate Buoyancy (Nov. 15, 2010)— Virtually nothing has been known about leatherback turtle diving strategies, but now scientists have discovered that leatherbacks regulate their buoyancy by varying the amount of air they inhale … > read more

How do diving marine mammals avoid decompression sickness? - Biology

Sarah Bedolfe
Marine mammals are well adapted to a deep-diving lifestyle, but they aren’t immune to decompression sickness.

Focusing on science, technology, engineering, and math (STEM), as they pertain to the ocean.

In a previous post, we discussed how humans can SCUBA dive underwater &ndash and even live there, with the help of bases such as Aquarius &ndash without suffering from the bends. Decompression sickness, known as the bends, occurs after the nitrogen a diver breathes enters the blood stream while at depth if the diver ascends to the surface too quickly and doesn&rsquot allow time to exhale the gas, the nitrogen bubbles up in the blood stream.

Typically this isn&rsquot a concern for people who freedive &ndash diving without an air tank, holding their breath. Since they don&rsquot get extra air at depth and they can&rsquot spend very long underwater, the body doesn&rsquot absorb enough nitrogen to cause such problems, but doing many repeated dives can be more dangerous. Symptoms of decompression sickness have been found in commercial freedivers, for example pearl harvesters, who make long, deep, and frequent dives.

For a long time, scientists were unsure if marine mammals could get the bends during long and repetitive deep dives &ndash or if they don&rsquot, how they avoided it. We know now that marine mammals typically don&rsquot get the bends, but that they can under certain conditions.

Photo by Joyce (headharbourlight) via Flickr, Creative Commons License.

Diving response is a reflex that all vertebrates have, including humans, but it is most strongly developed in diving animals. They automatically slow their heart rate and send blood flow away from the muscles and to the most important organs such as the brain to conserve oxygen. They also have high levels of hemoglobin and myoglobin, which store oxygen, in their blood.

Their main defense against the bends is that their lung structure can collapse under high pressure. This forces the air away from the alveoli and into the upper airways where the gas can&rsquot enter the bloodstream, and that&rsquos what keeps the blood from absorbing too much nitrogen at depth. This also preserves a reservoir of oxygen that becomes available again during the trip back to the surface.

While it has been known for a long time that marine mammals can collapse their lungs, a study published just last month was the first to measure it. Researchers were able to place a data logger on a female California sea lion, which would keep track of the partial pressure of oxygen in its main artery. A decrease in the oxygen pressure indicates lung collapse (because the air leftover in the lungs would be cut off from the blood stream), so they could see how its lung collapse corresponded to dive patterns.

Photo by John Norton via Flickr, Creative Commons License.

The sea lion in the study did 48 dives of about six minutes each, and collapsed its lungs each time around 225 m (731 ft) deep. The sea lion could keep going to about 300 m (994 ft) before heading back to the surface. Oxygen pressure increased again around 247 m (802) feet, showing that it was drawing air back from the upper airways into the alveoli. The researchers also found that the sea lion inhaled more air and collapsed its lungs at a deeper depth if it was going on a deeper dive.

What are the conditions, then, under which a marine mammal can get the bends? A 2011 study that found symptoms of bubble formation in the bodies of beached whales, dolphins, and seals showed that their defenses against decompression sickness don&rsquot always work. The authors suggest that conditions, such as cold water, could force the whales to balance other needs (eg. circulation for warmth) with the need to dive safely.

Photo by Willy Volk via Flickr, Creative Commons License.

There is another important factor: the symptoms of the bends were often found in the carcasses of animals that were exposed to extremely loud noise, such as naval sonar testing. Sonar has been linked to marine mammal deaths for a long time, though scientists don&rsquot know yet exactly how or why. It may disorient them or force them to surface too quickly.

While there is a lot that we still don&rsquot know about how marine mammals dive, we do know that even these animals who are so well adapted to a deep-diving lifestyle, aren&rsquot immune to decompression sickness &ndash and human activities may even be causing it.


Secrets of the animals that dive deep into the ocean

Cuvier's beaked whales dive deeper than any other animal, going down almost 3km. How do they survive in the crushing pressure?

When it comes to diving deep, Cuvier's beaked whales lead the pack. In a study published in March 2014, scientists tracked these typically elusive whales and reported one whale dived to the dizzying depths of 2,992 m (9,816ft). The same whale stayed underwater, without taking a single breath, for 138 minutes.

The feat was exceptional, breaking new mammalian dive records in two categories simultaneously. But while the Cuvier's beaked whales have proved themselves as the champion divers, other marine mammals have also evolved, and honed, the ability to dive deep and long. Sperm whales routinely dive between 500m and 1000m, Weddell seals go to 600m, and elephant seals can hold their breath for two hours.

"It's just astonishing what these animals can do," says Andreas Fahlman of Texas A&M University in Corpus Christi. "These animals do these deep dives day in, day out, sometimes repeating the dives a number of times a day, and don't seem to have any problems with it. So the constant question we ask ourselves is: how do they do that?"

Animals dive deep for one reason, and one reason alone: to get food, says Randall Davis, who is also at Texas A&M University. "These whales are making these dives to tremendous depths because there's some payback in terms of a food resource," Davis says. "Animals don't do these kinds of things for fun. This is how they make a living."

But it's a challenging way to make a living. The most immediate problem is the extreme, crushing pressure. At 1000m down, a Cuvier's beaked whale experiences 100 times the pressure that they do at the surface, enough to completely compress the air in their lungs.

To avoid this, Randall says, they have rib cages that can fold down, collapsing their lungs and reducing air pockets. Then, right before diving, these mammals exhale 90% of the air in their lungs. This also reduces their buoyancy, making it easier to dive.

But that introduces a new problem. With little oxygen in their lungs, the whales have to be thrifty when it comes to using the gas on their dives. "They are very frugal," Fahlman says. "They're just really, really tightly holding onto this oxygen and trying to use it as conservatively as possible."

To stop using so much oxygen, diving mammals can stop their breathing and shunt blood flow from their extremities to the brain, heart, and muscles. They also shut down digestion, kidney and liver function.

Finally, they lower their heart rate. Most mammals can do this when they dive, even humans. But in marine mammals the slowdown can be extreme. Scientists have measured the heart rate of diving Weddell seals at a mere four beats per minute.

The animals also adapt their behaviour to conserve oxygen by reducing how much they move. In 2000, Terrie Williams of the University of California, Santa Cruz and colleagues attached miniature cameras to Weddell seals, a bottlenose dolphin, an elephant seal and a blue whale. They found that the animals simply glided downwards without moving a muscle. Their shrunken lungs reduced their buoyancy, allowing them to sink rather than swim.

But it's not enough to just be stingy with oxygen. Once they're in deep water, divers like Cuvier's beaked whales have to sneak up on, and overcome, their prey. For that, they need to find some oxygen.

Fortunately, they have a supply: they store oxygen in their blood and muscles. Marine mammals have a higher percentage of oxygen-storing red blood cells than most mammals, making their blood thick and viscous. They also have a high blood-to-body-volume ratio. "They simply have a bigger savings account than we do," Fahlman says.

But this shouldn't be enough. "From what people have estimated for the oxygen stored, and the rate at which they are consuming this oxygen, it shouldn't be possible for animals to dive to these depths at all," says Michael Berenbrink of the University of Liverpool in the UK.

Then in 2013, Berenbrink made a startling discovery about diving animals' muscles. Like all mammals, their muscles contain a protein called myoglobin that stores oxygen and gives meat its red colour. Myoglobin is ten times more concentrated in the muscles of diving animals than it is in human muscles. It is so concentrated in whales that their flesh appears almost black.

But there should be a limit to the amount of myoglobin that muscles can contain. If too many of the molecules pack into a small space, they could stick together. Such clumping can cause serious diseases in humans, such as diabetes and Alzheimer's. Yet Berenbrink found that diving animals' muscles seemingly carry too much myoglobin.

What's their secret? Berenbrink found that the myoglobin of diving animals is positively charged. Since like charges repel each other, the positively-charged myoglobin molecules don't stick together. This means that huge amounts of myoglobin can be packed in, supplying plenty of oxygen.

Berenbrink found that all the diving mammals he studied had positively-charged myoglobin, although some had larger positive charges than others. The highest concentrations of myoglobin occur in the muscles needed for swimming, exactly where the divers need it the most. What's more, genetic analyses suggested that beaked whales should have the highest levels of myoglobin, as we would expect.

But while Berenbrink's work has found a veritable built-in oxygen tank in divers, he says we still don't know whether this tank provides enough for the long dives made by beaked whales. "There is still a lot that we don't know," Berenbrink says.

Even if the diving mammals do have enough oxygen, they're still not out of the woods. They must also deal with a disorder called decompression sickness, or "the bends". In humans, the bends can be fatal. And it turns out marine mammals are also at risk.

When a human scuba diver is at depth, gases dissolve in their blood. If the diver then comes up too quickly, the pressure drop causes gas bubbles to emerge from the bloodstream and get lodged in capillaries and critical organs. This causes discomfort and pain, and sometimes death.

Late in 2002, 14 beaked whales washed ashore together on a beach in the Canary Islands. When scientists performed an autopsy on 10 of the whales, they found deadly tissue damage that is usually associated with pockets of gas in vital organs. That suggested the whales had the bends.

Scientists had thought diving mammals were immune from the condition, even though they had found such bubbles before in stranded animals. Between 1992 and 2003, researchers found bubble-associated tissue injury in dolphins, porpoises and a single Blainville's beaked whale washed up on British shores.

The question was finally settled in 2013, when Daniel García-Párraga of Oceanografic in Valencia, Spain and his colleagues diagnosed the bends for the first time in live marine animals: loggerhead sea turtles.

The turtles had been accidentally caught in commercial fishing nets and bought in by local fishermen. Of the 21 that arrived alive, 9 showed signs of spasticity. CT scans revealed bubbles in the turtles' organs.

It's easy to diagnose decompression sickness: simply put the animal under higher pressure and see if the symptoms clear. To that end, García placed the two smallest turtles in the lab autoclave and recompressed them using similar protocols to those used for human divers. The turtles made a full recovery and García eventually released them back into the wild.

"That is the first time anybody anywhere in the world has achieved a clinical diagnosis of decompression sickness in a live marine vertebrate," says Michael Moore of the Woods Hole Oceanographic Institution in Massachusetts.

The finding is important for efforts to conserve sea turtles. We now know that turtles caught up in fishing nets may suffer from the bends, and need treatment before being let go. If fishermen simply untangle them from the nets and release them immediately, the turtles may die of decompression sickness.

Outside of fishing, though, it is hard to see why marine mammals would ever get the bends. A 2011 study by Fahlman and his colleagues indicated that they are always susceptible to the condition, yet in normal conditions are able to avoid getting it. Decompression sickness happens if they ascend too quickly, so surely they should have evolved not to do that. But maybe something is forcing them to rush to the surface?

In the 2002 beaching, a series of military exercises involving sonar took place in the region just four hours earlier. Since that incident, researchers have noted the links between sonar activity and strandings of marine mammals on beaches in the Mediterranean Sea, the Canary Islands, and the Bahamas.

In theory, if whales are 1000m or 2000m down, the noise of sonar could send them rocketing up to the surface. If they came up too quickly, their anti-decompression mechanisms might not keep up. But we can't confirm this, Fahlman says. "No one even understands how they avoid the bends, let alone how they then go on to get the bends in certain situations," Fahlman says.

Whales do seem to dislike sonar. When scientists exposed Cuvier's beaked whales to simulations of sonar for a 2013 study, the whales stopped fluking and echolocating, and swam away rapidly and silently. They then stayed underwater longer than normal.

"But really what does that show?" asks Fahlman. "It doesn't tell us anything about how the whales might behave underwater, at great depths."

Fahlman says the only way to understand why the whales get the bends is to figure out their normal behaviour and physiology, in particular how they cope when deep diving. But that is no mean task, not least because whales are far too big to ever study in a laboratory.

These studies could have unexpected benefits, adds Fahlman. By unravelling the physiology of extreme diving, researchers may figure out how to treat certain clinical conditions in humans. One example is atelectasis, in which a person's lungs collapse, obstructing breathing. Marine mammals' extreme dives may point the way to a cure.

"They're diving to depths that are absolutely phenomenal," Fahlman says. "With our current knowledge of physiology, they're going way over and beyond what they're supposed to be able to do."


Coping with lots of fat: A marine mammal’s perspective

Imagine this scenario: You’re going for a jog outside, but seeing some snow on the ground, you decide to put on a thermal long-sleeve shirt underneath your sweatshirt. Right as you step out the door, you sure are glad you added that extra layer. After a few minutes into your jog, you notice you’re breathing heavy and your heart is beating faster (…especially if you’re out of shape). Your skin might get red, feel hot and flushed, and after a little while, you’ll probably also start sweating. These physiological responses keep your body fueled with oxygen during your aerobic workout while also preventing you from overheating. But you still start to feel slightly uncomfortably warm.

What do you do? Easy enough, just take off the extra layer!

Now imagine that ‘extra layer’ came in the form of thick blubber as it does for marine mammals. How do marine mammals cope with variable thermoregulatory demands—conserving heat while diving to cold depths but dissipating any excess heat when actively swimming? Whales, dolphins, seals, and sea lions are endothermic mammals, just like we are, and have to regulate their body temperature. But, they cannot just easily take off their blubber layer like we do with our clothes.

Living in a marine environment presents even more challenges for thermoregulating. Because sweating in water is pointless, many marine mammals don’t even produce sweat. Most marine mammals also spend a majority of their time underwater where they don’t have the leisure of breathing heavy like us to get more oxygen while actively swimming. To conserve oxygen while diving, marine mammals decrease their heart rate and restrict blood flow to only the most critical organs (brain, lungs, and heart). With no blood flowing to their skin, the heat generated from exercising stays in their core while their skin keeps cold, usually within a couple degrees of the water temperature.

Considering these adaptations, here’s my curiosity: if a marine mammal becomes overheated, how can they thermoregulate while balancing their physiological adaptations for diving?

This is what I am studying as a graduate student—the seemingly paradoxical physiological adaptations for diving and thermoregulation of marine mammals—and I happen to be at the perfect place to study the physiology of freely diving marine mammals. Año Nuevo Reserve is home to a colony of northern elephant seals and is only 30 minutes north of the University of California, Santa Cruz campus. The Costa Lab at UCSC has been studying this population for over 40 years and has all the necessary research permits. As a new graduate student in the lab, I get to work with marine mammal experts and contribute to the lab’s body of research. My research will investigate the thermoregulatory response of diving marine mammals and what better species to study than one of the deepest diving marine mammals—northern elephant seals.

When planning a research project, finding the best model species is just the first step, and I happened to luck out by having elephant seals at our door step. The next step is to figure out what data are needed to address your question or test a specific hypothesis and how you will collect it.

This is where collaboration comes into my work—I am lucky to get to work with Alaska SeaLife Center’s Science Director, Dr. Markus Horning. In my previous 60° North Science blog, I described the morning of my first translocation study where I attached biologgers to two juvenile northern elephant seals. The biologgers that I used were custom-built by Wildlife Computers and designed by Dr. Horning and Dr. Kate Willis to specifically measure heat flux from sensors placed on an animal’s skin (Willis and Horning 2004). Heat flux is how much heat is transferred between the seal’s body surface and the surrounding water, which basically tells you when the animal is gaining or losing heat to its environment. This is exactly the kind of data I needed to begin to address my question. Since these heat flux biologgers were also designed for independent, long-term attachment, this made them perfect for collecting data from freely diving animals.

Until these heat flux biologgers were invented, these measurements had only been possible on trained animals with human assistance, which prevented getting measurements from wild animals diving naturally. These heat flux biologgers have now been used on a few different species, including the ASLC’s Steller sea lions, wild Weddell seals, and, after my translocation study, juvenile elephant seals!

So, what did the data from the heat flux biologgers tell us about how marine mammals thermoregulate while diving? Read my next blog post to find out more about my first translocation study with elephant seals!

Written by: Arina Favilla, PhD Student, Ecology and Evolutionary Biology, University of California Santa Cruz.


How Do Marine Mammals Avoid the Bends?


“©Freedom Breach” is an image courtesy of © Pasha Reshikov.

Deep-diving whales and other marine mammals can get the bends—the same painful and potentially life-threatening decompression sickness that strikes scuba divers who surface too quickly. A new study offers a hypothesis of how marine mammals generally avoid getting the bends and how they can succumb under stressful conditions.

Scientists once thought that diving marine mammals were immune from decompression sickness, but a 2002 stranding event linked to navy sonar exercises revealed that 14 whales that died after beaching off the Canary Islands had gas bubbles in their tissues—a sign of the bends…

Marine noise pollution stresses and confuses fish Science Daily (08-10-2017)
Increased noise pollution in the oceans is confusing fish and compromising their ability to recognise and avoid predators…

Motor-boat noise changed the behavior of fish parents Science Daily (06-06-2017)
The sound of motorboat engines disturbed coral reef fish so acutely it changed the behavior of parents, and stopped male fish properly guarding their young, feeding and interacting with their offspring, new research has found…

Whales turn tail at ocean mining noise Science Daily (08-17-2017)
A new international study has measured the effect of loud sounds on migrating humpback whales as concern grows as oceans become noisier. Scientists have said one of the main sources of ocean noise was oil and gas exploration, due to geologists firing off loud acoustic air guns to probe the structure of the ocean floor in search of fossil fuels…

Sonic Sea, Film Documentary NRDC May 19th, 2016
Oceans are a sonic symphony. Sound is essential to the survival and prosperity of marine life. But man-made ocean noise is threatening this fragile world. “Sonic Sea” is about protecting life in our waters from the destructive effects of oceanic noise pollution…

Accoustic Pollution and Marine Mammals, Nature
In the Canary Islands, 14 beaked whales washed ashore bleeding from the ears. All eventually died. A post-mortem examination revealed that the whales showed signs of decompression sickness (what scuba divers call “the bends”). Decompression sickness can occur when a mammal swims to the ocean’s surface too quickly, and the change in pressure produces lethal nitrogen gas bubbles that clog its blood vessels. Evidence of acute decompression sickness indicates unusual behavior. Over the past 40 years, cumulative research across the globe has revealed a coincidence between naval sonar testing events and acute decompression sickness in beached marine mammals…

A Silent Victory For Marine Mammals, On Earth Magazine (04-03-2015)
A federal judge stands up to the noisy navy for the sake of marine mammals…

“FREIGHTENED – The Real Price of Shipping,” a movie by multi award-winning filmmaker Denis Delestrac-©-2016 (03-31-2016)
90% of the goods we consume in the West are manufactured in far-off lands and brought to us by ship. The cargo shipping industry is a key player in world economy and forms the basis of our very model of modern civilisation without it, it would be impossible to fulfil the ever-increasing demands of our societies. Yet the functioning and regulations of this business remain largely obscure to many, and its hidden costs affect us all. Due to their size, freight ships no longer fit in traditional city harbours they have moved out of the public’s eye, behind barriers and check points…


Watch the video: Dekompressionskrankheit 8 6 TED (July 2022).


Comments:

  1. Reave

    I agree with you, thanks for the help in this question. As always all ingenious is simple.

  2. Atif

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