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Why do stranded marine mammals die so quickly?

Why do stranded marine mammals die so quickly?


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Mammals have lungs, so do marine mammals. Nevertheless some marine mammals seem to die rather quickly when they strand on a beach.

As they have lungs and can breath while on land, why do they die so quickly? Not being in water only restricts them from food.

Do they maybe try to get back into the water so rudely that they get hurt by rocks and/or break bones? Pressure difference doesn't seem to be a problem as they can jump out of the water as well.

I was wondering after reading this article on stranded pilot whales that got spot but died rather quickly after.


In the case of whales, I always thought that it was something to do with the fact that they rely upon buoyancy to support their weight and this seems to support that view:

When whales, including small whales or dolphins become stranded on beaches they suffer from the pressure of their own weight on their organs,in the water they are weightless. They also suffer from overheating as they have blubber that insulates them in the water and outside of the water causing them to overheat. This is why we place wet towels and cold water on their fins and flukes when do they strand to help keep their body temperature down. Unfortunately most stranded whales do not survive once they have beached themselves.


That's not exactly true, you are generalizing. For example seals are marine mammals (that's a rather large non-official group I think) and they don't die so quickly.

Anyway, breathing is not the only thing necessary for survival. If you leave a human inside a 50°C room he can still breath but won't live for long.


Why do marine mammals not die of infection more often?

You see all the time images of whales and seals and other marine mammals with injuries due to boats and stuff that have healed. There was even that picture of that whale with a fin injury that was photographed 30 years later or something like that. I would think being submerged in dirty water would make those wounds dangerously infected though. Are humans just super fragile mammals and the rest can handle wounds much better?

> I would think being submerged in dirty water would make those wounds dangerously infected though.

What makes you think the water is dirty?

Well, ignoring the bit about dirty water for the moment–how do you know that they don’t? If a whale or whatever gets injured by a boat and then dies, the corpse will sink to the bottom of the ocean and never be seen again. There’s a degree of confirmation bias here due to that.

1)they probably do die of infection, a lot, but most of these cases are probably lost in the vastness of the ocean and what you are talking about is a tiny almost impossible chance of cases that we see.

2) most injuries sustained are from predators and chances are that predators will finish the job and kill off mammals with a wound. Again the cases seen are a tiny fraction of all cases

In the same way that most humans have

a set of defenses for “bad stuff” that is present in our environment, animals have done similar things for their environment. Some animals have biology that is simply incompatible with the “bad stuff” that surrounds them. Can’t get a blood infection if you don’t use blood, for example. Another factor is that most animals have a ‘hide’ of some sort that is very tough, and designed to ‘take damage’ and not put the rest of the body at risk. Plus, the size is also easy to leave out of the equation. A scar that is 10m long might look bad to us, but the overall damage to the body might be 1% overall.

It is easy to apply ‘human problems’ to animals, but we are honestly waaaaaay more fragile than most animals on this planet. Most animals are far more robust than humans are, even a few hours after being born. The immune system has to be, since animals have to rely on it nearly exclusively for fighting off disease. This is one contributing factor on why viruses that jump from animals to humans are EXTREMELY bad. See most of the deadly plagues of humanity. In addition to being 100% not anything that our bodies have ever dealt with, it is also assuming that it is in an animal that has a super powerful immune system–and so it hits hard, fast, and doesn’t stop.


Why Do Whales and Dolphins Strand?

Pilot whales, sperm whales, beaked whales and deep-sea dolphins are the marine mammals most commonly involved in mass strandings. Baleen whales, on the other hand, a group to which all big whales except the sperm whale belong, strand very rarely.

If these mammals become stranded, they can dry out, overheat, suffocate or suffer severe inner injuries because of their enormous dead weight.

Individual strandings have been observed at many locations, while most mass strandings have been registered in Western Australia, New Zealand (with up to 300 stranded whales annually), and on the east coast of North America and Patagonia (Chile). Occasionally, however, there are also mass strandings in the North Sea.

How Do Whales and Dolphins Navigate?

Like migratory birds, some whale species travel great distances every year. In winter, whales migrate from the cold northern seas to warmer waters in the south, and whales from southern waters move to the north in the same season. Months later, they then begin to travel back home.

The smaller toothed whales, such as dolphins, have a powerful underwater sonar. They orient themselves on their journeys by emitting sound waves in the form of clicking noises. When these sound waves collide with an object, they are reflected back as echoes to the animals' ears, which in the case of whales are shielded from the skull in foam-filled chambers inside the body to enable spatial hearing. The faster the sound returns, the closer the prey, an obstacle or the coast.

However, in the case of the large baleen whales, which have horn plates (baleen) instead of teeth in their upper jaws for filtering krill, animal plankton and small fish from the water, this underwater sonar is not very highly developed.

This echolocation works very well as a rule. However, sound reflection does not function reliably in certain circumstances, particularly when there are shallow or semicircular bays, sandy underwater embankments or silt banks. These types of coasts and obstacles do not produce an unambiguous echo from any particular direction, so the warning system fails.

What Influence Does the Earth's Magnetic Field Have?

Whales such as the pilot whale do not use just underwater sonar to orient themselves, but — again, like migratory birds — seem to rely on the lines of the earth's magnetic field, as their migration routes often run parallel to those lines. The slight fluctuations of the earth's magnetic field appear to function like a kind of map.

Magnetite crystals have been found in the skulls of these animals. The whales could be confused by disturbances of the geomagnetic field near the coast. Magnetic fields running perpendicular to the mainland are also thought to play a role in mass strandings of whales in certain coastal regions.

Every few years, solar storms and sunspots that occur amid heightened activity on the sun's surface also cause fairly large changes in the Earth's magnetic field. It is at such times that sperm whales, for example, which also use geomagnetism as a natural navigation system, get lost and become stranded in the North Sea.

Why Do Whales and Dolphins Become Stranded?

Navigational errors are thus believed to be the main cause of whale strandings, but all the reasons have not yet been conclusively investigated.

One of them is certainly the social behavior of many whale species, which travel in groups, so-called pods, and are guided by a leader. For example, in the case of sperm whales, a male leads the way from the Arctic Ocean back into warmer waters. By contrast, when orcas are on their travels, a mother or grandmother leads the group.

If leaders lose their orientation, perhaps because they are confused or because parasites have attacked their ears, rendering them incapable of hearing the echoes of the clicking sounds that have been sent, the accompanying animals will follow them in the wrong direction. If a leader is stuck in shallow waters, the rest of the group stays with it, even if this means their certain doom.

Sometimes, as has been observed, for example, with orcas on the South African coast, this group cohesion can go so far that whales who have already been saved after a mass stranding return to the beach if another stranded whale calls for help.

But strandings can also have other natural causes. Sometimes, smaller dolphins become beached because they have taken refuge from orcas and other predators in shallower waters or because they have ventured too far into shallow areas when hunting shoals of fish.

Occasionally, individual animals are also washed ashore dead after being previously injured by collisions with ships, fishing nets or shark attacks or becoming ill from infections or parasite infestation.

Which Human Influences Exacerbate the Situation?

In addition to natural factors, man-made underwater noise from ships, icebreakers, drilling platforms or military sonar equipment can also massively impair the orientation and communication of marine mammals. They flee the strong sound waves in a state of confusion. And since the density of water is much higher than that of air, sound propagates underwater about five times faster than in the air.

Military sonar operations employing very loud sounds have particularly drastic effects. After NATO maneuvers, for example, beaked whales have washed up dead on the coasts of Cyprus, the Canary Islands and the Bahamas. The sonars, which are louder than 200 decibels, triggered the formation of gas bubbles in the blood vessels and organs of marine mammals (as happens with diving sickness), obstructing the blood supply and leading to their death.

How Can You Help Stranded Whales and Dolphins?

When a whale stranding is discovered, there is usually not much time left. Teams of helpers can do little more than try to cool the stranded animals, keep them moist and combine forces to get the heavy animals back into the sea as quickly and gently as possible.

In some countries, hotlines have been set up so that as many helpers as possible can be mobilized quickly. For many exhausted animals, however, even these immediate measures often come too late.


Why don't whales and other marine animals get the bends while surfacing quickly?

In the case of humans, surfacing too quickly is catastrophic, and can lead to a whole slew of problems but this doesn't seem to be the case in marine animals like this whale why not?

Hey, this is a cool question with an easy answer.

Whales, dolphins and mammals do not get the bends (Decompression Sickness) because they do not breath air at depth. Its the same reason that swimmers and free divers don't get the bends.

Divers get the bends by breathing a compressed gas (at 10m/33ft, air is twice as dense as it is at the surface, called an atmosphere or ATM). By breathing that for a period of time, you absorb more oxygen and nitrogen that your body is built for. Rapidly ascending (like the whale in the gif) doesn't give time for that built up nitrogen to escape through your skin, lungs, ears, etc, causing bubbles to form in your blood, joints, and in severe cases spine or brain.

When a swimmer or a whale dives down for 5 minutes, 10 minutes, an hour, whatever. Their bodies are only using one breath's worth of air, no matter how deep they are, as they took that breath of air at the surface.

Certain fish, however, can get something similar to the bends. There are some species that use a gas pouch for buoyency control (called a swim bladder or air bladder), and by pulling them from depth, that gas pouch expands, causing the pouch to expand and rupture. This causes something called an embolism, which is gas in your chest cavity. Even if they go back to depth, the gas is now floating around in their chest, and most likely they will die.

This is also the reason all divers are taught to NEVER hold your breath when scuba diving. Your lungs could rupture, causing (among other things) an air embolism in your chest, crushing your other lung, heart, or other vital organs if you ascended faster than the air could escape.

Source: Dive instructor, part of our training. Hope this helps! Dive safe (and don't worry about the bends when swimming!)


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."


Why do stranded marine mammals die so quickly? - Biology

I watched a sea lion die last summer. The large animal was emaciated, its spine and ribs visible below its fur. Its hind limbs were immobile as it dragged itself from the shore to the water. Once in the harbor, without the use of its rear flippers, the sea lion struggled to stay afloat. It sank, resurfaced and sank again.

I called a hotline, but it was too late. The animal never came back up.

I later learned that it probably had an advanced form of cancer. This particular cancer starts in the genitals and then attacks the spine before spreading throughout the body. It’s extremely common — in fact, sea lions have one of the highest rates of cancer among all wild animals. Scientists are just beginning to understand the causes.

A California sea lion, named Charlie Winston, stranded on a beach in California. Severe cancer had spread throughout her body and made her too sick to swim.

For more than 20 years, Dr. Frances Gulland has collected samples of this cancer. Gulland didn’t know if she’d ever learn what caused it, or be able to treat it, but she had foresight. So she gathered the samples and stored them, and hoped that one day there would be a way to study them.

Today, those samples and others provide a gold mine of information and may help us better understand how cancers progress, not just in sea lions, but in humans too.

Gulland's predecessors at the Marine Mammal Center in Sausalito, California, first noticed the disease around 30 years ago. The Marine Mammal Center rehabilitates stranded sea lions, otters and seals found along the coast of California, and dissects and studies the animals that wash up dead.

About 20 percent of those dead animals had the cancer, which is perhaps second only to rate of facial cancer among Tasmanian devils.

This histopathology of a sea lion kidney shows four large, cancerous masses.

Scientists knew that for cancer to be as common as it is among sea lions, something had to be causing it. But it wasn’t clear what. So for much of her career, Gulland has spearheaded the effort to pinpoint the cause of the cancer.

Evidence points to three possible culprits: a sexually transmitted herpesvirus, pollutants like PCBs and DDT, and genetics. Today, researchers think some combination of the three is responsible.

All of the animals that develop the cancer have the virus. But that doesn’t mean the virus is the cause, said Dr. Alissa Deming, a veterinarian and researcher at the Dauphin Island Sea Lab. That’s because they also found the virus in seemingly healthy animals. “It’s hard to tease out if the virus is just coincidentally there, because viruses exist. I’m trying to tell, definitively, if it’s causal.”

In humans, there’s another cancer caused by a closely related herpesvirus. In patients with late-stage AIDS, the normally harmless virus causes a serious form of cancer.

Could it be that something was suppressing the immune system of the sea lions, which allowed the herpesvirus to penetrate more deeply into their cells?

Deming and Gulland tested cancerous sea lions for the presence of PCBs and DDT, two pollutants that are known to suppress immune systems. Sure enough, sea lions that had high levels of those pollutants were 6 to 8 times more likely to have the cancer.

The fuzzy area in this radiograph was thought to be cancer.

But even that doesn’t confirm the cause. Sea lions that die from the cancer are very thin and emaciated. Since PCBs and DDT build up in fat, the sick animals could appear to have higher exposure to pollutants simply because it’s more concentrated in their bodies.

“You can’t really do experiments on the sea lions. We can’t give them different exposures,” Deming said. “It’s such a dirty, hard thing to work out.”

PCBs and DDTs persist in the environment, especially in the sand just offshore, where they can enter the food chain. There’s no easy way to remove them.

So you can’t stop sea lions from being exposed to pollutants, you can’t stop them transmitting a herpesvirus, and you can’t treat wild animals for cancer. So what’s the point of the research?

“There are two things we get out of it,” Gulland said. “First, we’ve learned that it isn’t something we can do anything about. Imagine if it was a single pollutant accumulating in coastal waters, and we could stop that, and we didn’t know. It’s also another piece of evidence that PCBs and DDTs are harmful. The second is that it can give us insight into cancers in people, like the virally induced cancers in humans.”

Normally human cancers are studied in animals like mice. But sea lions are a lot more like humans.

“We’re both long-lived mammals, we both eat a lot of fish, we’re exposed to the same stressors. We get infected with similar viruses,” Deming said. In short, sea lions are a perfect model organism. And there are a lot of sea lions, so there are a lot of animals to study.

A lot of those severely ill animals end up at the Marine Mammal Center or another rehabilitation site. But since there’s no treatment, eventually the animal dies.

Superstition, a California sea lion, was brought to the Marine Mammal Center. Veterinarians suspected she had cancer, which was confirmed with a radiograph and ultrasound. She died just days after her rescue.

“As a veterinarian, it was really frustrating to have these animals come in, and they’re in such pain during end-stage disease,” Deming said. “That’s why I decided to go back to school and do my Ph.D. Otherwise, they’re going to be wasted. If we don’t do research on them, they’re just another number.”

These sea lions could help answer one of the biggest questions in cancer biology: Why do some tumors stay in one place and remain benign, while others metastasize and suddenly spread throughout the body? “That is a big black box in science, it’s really hard to study in humans or replicate it in an animal model,” Deming said.

In humans, as in most animals, it isn’t the initial cancer cells that kill you. It’s the cancer that spreads to other parts of the body. According to Deming, only about 10 percent of people will die from the initial tumor.

A unique opportunity to peer into that black box came unexpectedly, when Dr. Julia Burco, a wildlife veterinarian with the Oregon Department of Fish and Wildlife, reached out to Deming.

For a handful of years, ODFW had been removing sea lions that swam up the Columbia River and its tributaries. The animals ate endangered steelhead salmon that congregate at the base of Columbia River dams, waiting to for steelhead to swim up the fish ladder. Steelhead numbers were so low, that ODFW was prepared to try something radical: killing sea lions that returned to the dams multiple times, if they can't first be homed in an aquarium.

Burco saw this as an opportunity, a chance to see just how many seemingly healthy sea lions truly had the cancer. Since the initial lesions appear internally, there’s no way to check for them while the animals are alive.

Burco found that a lot of animals without any visible wounds could have cancer. About 90 percent of the animals she checked carried the virus. In the year that they sampled the most animals, 2017, they found the virus in 37.5 percent of sea lions.

This also gave Deming a chance to study cancerous cells before they became severe and spread. In ongoing research, she and Burco are looking at the genetics of the early and late-stage cancerous cells, to see if certain genes are turned on or off that allow the cancer to spread throughout the body. Then, she plans to look for similar genes in known human viruses and virally caused cancers.

“For me, it lets me sleep better at night, knowing I’m doing something with these animals that are coming in and dying,” Deming said. “I’m paying respect to that animal by learning as much as I can from it. We know we can’t save them all, but we can make them all matter."


Tutorial: Mammals &ndash Strandings

The term stranding refers to an aquatic animal observed in an inappropriate location, for example, an offshore species found inshore. Most often, stranded animals are found on a beach or in shallow water. Observations as far back as Aristotle [1] Aristotle. (1910). The History of Animals. (D. W. Thompson, Trans.). London: Clarendon Press. and illustrations from the Middle Ages show us that marine mammals have been stranding for millennia. There are many causes of strandings, such as disease, ship-strike, injuries, storms, and entanglement. Only very few strandings have been attributed to sound.

Drawing of a stranded whale in Katwijk, the Netherlands, in 1598. Image courtesy of World News Network.

In the U.S. alone, about 1,000 cetaceans and 2,500 pinnipeds strand annually. Some animals strand live and are returned to sea. Others die at sea or on shore. Animals may strand singly or in groups. When 3 or more animals strand together in time and place, it is called a mass stranding . Some species, such as pilot whales, mass strand regularly around the world.

Determining the cause of a stranding or death of a stranded animal can be difficult. Dead stranded animals are sometimes necropsied which is a thorough examination of the entire body. Scientists usually have little or no information about the animal&rsquos history or the circumstances that preceded the stranding. A cause of death can be determined in only about half of all stranding cases.

Total number of strandings of cetaceans (yellow bars) and pinnipeds (blue bars) in the U.S. each year from 1992-2002. Data provided by Janet E. Whaley and Teri K. Rowles, NOAA Marine Mammal Health and Stranding Response Program.

There is consensus that military sonar exercises have contributed to mass strandings of beaked whales [2] Filadelfo, R., Mintz, J., Michlovich, E., D&rsquoAmico, A., Tyack, P. L., & Ketten, D. R. (2009). Correlating military sonar use with beaked whale mass strandings: What do the historical data show? Aquatic Mammals, 35(4), 435&ndash444. https://doi.org/10.1578/AM.35.4.2009.435 [3] D&rsquoAmico, A., Gisiner, R. C., Ketten, D. R., Hammock, J. A., Johnson, C., Tyack, P. L., & Mead, J. (2009). Beaked whale strandings and naval exercises. Aquatic Mammals, 35(4), 452&ndash472. https://doi.org/10.1578/AM.35.4.2009.452 [4] National Research Council (U.S.) (Ed.). (2003). Ocean noise and marine mammals. Washington, D.C: National Academies Press. [5] Evans, D. L., & England, G. R. (2001). Joint Interim Report Bahamas Marine Mammal Stranding Event 15-16 March 2000. Washington, D.C.: Department of the Navy and Department of Commerce, National Oceanic and Atmospheric Administration. PDF . However, it is still not clear if it is simply the sound of the sonar , or other aspects of the military exercises, such as multiple ship maneuvers, that resulted in the strandings.

Mass strandings of beaked whales are rare, with only 136 mass stranding events reported from 1874 to 2004 [6] D&rsquoAmico, A., Gisiner, R. C., Ketten, D. R., Hammock, J. A., Johnson, C., Tyack, P. L., & Mead, J. (2009). Beaked whale strandings and naval exercises. Aquatic Mammals, 35(4), 452&ndash472. https://doi.org/10.1578/AM.35.4.2009.452 . Of these, two reported details on the use, timing, and location of sonar in relation to mass strandings. Ten other mass strandings coincided in space and time with naval activity that may have included military sonar. As of 2014, there are five additional documented events of beaked whale stranding in association with military sonar exercises [7] Ketten, D. R. (2014). Sonars and strandings: Are beaked whales the aquatic acoustic canary? Acoustics Today, 10(3), 46&ndash56. . All these events had three consistent features: (1) the stranding locations were less than 80 km from the 1,000-m depth contour (that is, where deep water occurs near shore) (2) they occurred in areas where beaked whale mass strandings had previously been reported and (3) all included Cuvier&rsquos beaked whale s, a species that does not commonly mass strand.

Although these beaked whale strandings were closely related in time and location to the use of military sonars by many nations, whether the sonar sounds caused the strandings has still not been determined. In five well-documented cases, there is sufficient information about the military exercises and the times and locations of the strandings to determine that multi-ship exercises with sonar contributed to the strandings. These events occurred in Greece (1996), Bahamas (2000), Madeira, Portugal (May 2000), and the Canary Islands (2002 and 2004). The necropsies that were performed (described below) found similar injuries, but none of the animals were found to have acoustic trauma . There are currently few peer-reviewed scientific publications that describe and discuss these strandings. The majority of authoritative information on these strandings can be found in official investigation reports of the events.

Locations of the five best-documented beaked whale strandings that coincided with military activities involving the use of sonars. Two minke whales also stranded during the incident in the Bahamas in 2000.

Additional details about standing events can be found on the DOSITS Marine Mammal Stranding page.


Strandings

The term stranding refers to an aquatic animal observed in an inappropriate location, for example, an offshore species found inshore. Most often, stranded animals are found on a beach or in shallow water. Observations as far back as Aristotle [1] Aristotle. (1910). The History of Animals. (D. W. Thompson, Trans.). London: Clarendon Press. and illustrations from the Middle Ages show us that marine mammals have been stranding for millennia. There are many causes of strandings, such as disease, ship-strike, injuries, storms, and entanglement. Only very few strandings have been attributed to sound.

Drawing of a stranded whale in Katwijk, the Netherlands, in 1598. Image courtesy of World News Network.

In the U.S. alone, about 1,000 cetaceans and 2,500 pinnipeds strand annually. Some animals strand live and are returned to sea. Others die at sea or on shore. Animals may strand singly or in groups. When 3 or more animals strand together in time and place, it is called a mass stranding . Some species, such as pilot whales, mass strand regularly around the world.

Determining the cause of a stranding or death of a stranded animal can be difficult. Dead stranded animals are sometimes necropsied which is a thorough examination of the entire body. Scientists usually have little or no information about the animal&rsquos history or the circumstances that preceded the stranding. A cause of death can be determined in only about half of all stranding cases.

Total number of strandings of cetaceans (yellow bars) and pinnipeds (blue bars) in the U.S. each year from 1992-2002. Data provided by Janet E. Whaley and Teri K. Rowles, NOAA Marine Mammal Health and Stranding Response Program.

There is consensus that military sonar exercises have contributed to mass strandings of beaked whales [2] Filadelfo, R., Mintz, J., Michlovich, E., D&rsquoAmico, A., Tyack, P. L., & Ketten, D. R. (2009). Correlating military sonar use with beaked whale mass strandings: What do the historical data show? Aquatic Mammals, 35(4), 435&ndash444. https://doi.org/10.1578/AM.35.4.2009.435 [3] D&rsquoAmico, A., Gisiner, R. C., Ketten, D. R., Hammock, J. A., Johnson, C., Tyack, P. L., & Mead, J. (2009). Beaked whale strandings and naval exercises. Aquatic Mammals, 35(4), 452&ndash472. https://doi.org/10.1578/AM.35.4.2009.452 [4] National Research Council (U.S.) (Ed.). (2003). Ocean noise and marine mammals. Washington, D.C: National Academies Press. [5] Evans, D. L., & England, G. R. (2001). Joint Interim Report Bahamas Marine Mammal Stranding Event 15-16 March 2000. Washington, D.C.: Department of the Navy and Department of Commerce, National Oceanic and Atmospheric Administration. PDF . However, it is still not clear if it is simply the sound of the sonar , or other aspects of the military exercises, such as multiple ship maneuvers, that resulted in the strandings.

Mass strandings of beaked whales are rare, with only 136 mass stranding events reported from 1874 to 2004 [6] D&rsquoAmico, A., Gisiner, R. C., Ketten, D. R., Hammock, J. A., Johnson, C., Tyack, P. L., & Mead, J. (2009). Beaked whale strandings and naval exercises. Aquatic Mammals, 35(4), 452&ndash472. https://doi.org/10.1578/AM.35.4.2009.452 . Of these, two reported details on the use, timing, and location of sonar in relation to mass strandings. Ten other mass strandings coincided in space and time with naval activity that may have included military sonar. As of 2014, there are five additional documented events of beaked whale stranding in association with military sonar exercises [7] Ketten, D. R. (2014). Sonars and strandings: Are beaked whales the aquatic acoustic canary? Acoustics Today, 10(3), 46&ndash56. . All these events had three consistent features: (1) the stranding locations were less than 80 km from the 1,000-m depth contour (that is, where deep water occurs near shore) (2) they occurred in areas where beaked whale mass strandings had previously been reported and (3) all included Cuvier&rsquos beaked whale s, a species that does not commonly mass strand.

Although these beaked whale strandings were closely related in time and location to the use of military sonars by many nations, whether the sonar sounds caused the strandings has still not been determined. In five well-documented cases, there is sufficient information about the military exercises and the times and locations of the strandings to determine that multi-ship exercises with sonar contributed to the strandings. These events occurred in Greece (1996), Bahamas (2000), Madeira, Portugal (May 2000), and the Canary Islands (2002 and 2004). The necropsies that were performed (described below) found similar injuries, but none of the animals were found to have acoustic trauma . There are currently few peer-reviewed scientific publications that describe and discuss these strandings. The majority of authoritative information on these strandings can be found in official investigation reports of the events.

Locations of the five best-documented beaked whale strandings that coincided with military activities involving the use of sonars. Two minke whales also stranded during the incident in the Bahamas in 2000.

Greece 1996: In May, 1996, twelve Cuvier&rsquos beaked whales stranded along 38 kilometers of the Greek coastline in the Mediterranean Sea [8] Frantzis, A. (1998). Does acoustic testing strand whales? Nature, 392(6671), 29&ndash29. https://doi.org/10.1038/32068 . This stranding coincided with a nearby military exercise conducted by the SACLANT Centre, a scientific research organization associated with the North Atlantic Treaty Organization (NATO). The exercise used sonars at frequencies of 450-700 Hz and 2.8-3.3 kHz. This incident is described in both a NATO report [9] D&rsquoAmico, A., & Verboom, W. (1998). Summary Record and Report, SACLANTCEN Bioacoustics Panel, La Spezia, Italy, 15-17 June 1998. SACLANT Undersea Research Centre. and in a published scientific paper [10] Frantzis, A. (1998). Does acoustic testing strand whales? Nature, 392(6671), 29&ndash29. https://doi.org/10.1038/32068 . The stranding responders in the area did not have enough equipment or skilled personnel to perform necropsies at the time and did not obtain the necessary tissue samples to determine the cause of death.

Bahamas 2000: Fourteen beaked whales, one spotted dolphin, and two minke whales were reported stranded in the Northern Bahamas Islands on March 15 and 16, 2000. Six beaked whales and 1 spotted dolphin died during this event. The strandings occurred within a 36-hour period and along a 240-km arc following the passage of five U.S. Navy ships taking part in an exercise that also used mid-frequency (1-10 kHz) sonars. The incident has been described in a report issued jointly by the U.S. Navy and the National Marine Fisheries Service [11] Evans, D. L., & England, G. R. (2001). Joint Interim Report Bahamas Marine Mammal Stranding Event 15-16 March 2000. Washington, D.C.: Department of the Navy and Department of Commerce, National Oceanic and Atmospheric Administration. PDF , a formal necropsy report by scientists and veterinarians [12] Ketten, D. R. (2005). Beaked Whale Necropsy Findings for Strandings in the Bahamas, Puerto Rico, and Madeira, 1999-2002 (No. WHOI-2005-09) (p. 36). Woods Hole Oceanographic Institution. PDF , and a peer-reviewed publication of the necropsy results [13] Ketten, D. R., Rowles, T., Cramer, S., O&rsquoMalley, J., Arruda, J., & Evans, P. G. H. (2004). Cranial trauma in beaked whales. European Cetacean Society Newsletter, 42, 21&ndash27. . The spotted dolphin stranded on the opposite side of the island chain from the beaked whales and was found to be malnourished with evidence of chronic, debilitating disease. It was decided that this animal&rsquos stranding was coincidental and unrelated to the mass stranding event. In contrast, the beaked whales that stranded were all in good condition with no evidence of significant disease. Blood deposits were found in and around the ears in several of the animals, but this was not caused by acoustic trauma. The reports concluded that the animals died from hyperthermia .

Madeira 2000: Three Cuvier&rsquos beaked whales mass stranded near Madeira, Portugal between 10 and 14 May 2000 [14] Freitas, L. (2004). The stranding of three Cuvier&rsquos beaked whales, Ziphius cavirostris, in Madeira archipelago. European Cetacean Society Newsletter, (42), 28&ndash32. . A fourth animal was reported floating in the water by a fisherman, but it did not come ashore. A NATO naval exercise off Portugal started just one day prior to the stranding (May 9 to May 14, 2000). The head of one beaked whale was in adequate condition to be examined [15] Ketten, D. R. (2005). Beaked Whale Necropsy Findings for Strandings in the Bahamas, Puerto Rico, and Madeira, 1999-2002 (No. WHOI-2005-09) (p. 36). Woods Hole Oceanographic Institution. PDF . It was found to have blood in and around the eyes, ears, and brain. This animal and another that were also examined on site were also found to have lung hemorrhaging .

Canary Islands 2002: In September, 2002, a mass stranding of fourteen beaked whales occurred in the Canary Islands. This stranding began about four hours after the start of a nearby NATO naval exercise involving ships of many nations that were using several types of mid-frequency sonar. The details of the sonar transmissions that occurred are not available. Ten of the stranded animals were found to have gas bubbles and hemorrhages in several organs [16] Jepson, P. D., Arbelo, M., Deaville, R., Patterson, I. A. P., Castro, P., Baker, J. R., &hellip Fernández, A. (2003). Gas-bubble lesions in stranded cetaceans. Nature, 425(6958), 575&ndash576. https://doi.org/10.1038/425575a [17] Fernández, A., Edwards, J. F., Rodríguez, F., de los Monteros, A. E., Herráez, P., Castro, P., &hellip Arbelo, M. (2005). &ldquoGas and fat embolic syndrome&rdquo involving a mass stranding of beaked whales (Family Ziphiidae) exposed to anthropogenic sonar signals. Veterinary Pathology, 42(4), 446&ndash457. https://doi.org/10.1354/vp.42-4-446 .

Canary Islands 2004: Four Cuvier&rsquos beaked whales were found floating nearshore or stranded on the northern Canary Islands between 21 and 26 July 2004. These strandings occurred one week after the NATO military exercise MEDSHARK/Majestic Eagle &rsquo04 off the Atlantic coast of Morocco. The naval exercise involved several warships that used mid-frequency sonar (2-10 kHz) in different areas and on different days, from July 11 to July 15, 2004. Three of the four whales were necropsied (the fourth whale found stranded on July 26 was too decomposed for analysis). The three necropsied whales were all in good condition with no evidence of disease. Microscopic gas bubbles were detected within many tissues, but it was not possible to determine if these were the result of decomposition or another process. Fat emboli , which are not associated with acoustic trauma, were detected in the lungs, kidneys, liver, and lymph nodes of all three animals and probably contributed to the whales&rsquo rapid deaths [18] D&rsquoAmico, A., Gisiner, R. C., Ketten, D. R., Hammock, J. A., Johnson, C., Tyack, P. L., & Mead, J. (2009). Beaked whale strandings and naval exercises. Aquatic Mammals, 35(4), 452&ndash472. https://doi.org/10.1578/AM.35.4.2009.452 [19] Fernández, A., Sierra, E., Martin, V., Mendes, M., Sacchinni, S., Bernaldo de Quiros, Y., &hellip Arbelo, M. (2012). Last &ldquoatypical&rdquo beaked whales mass stranding in the Canary Islands(July, 2004). Journal of Marine Science: Research & Development, 02(02). https://doi.org/10.4172/2155-9910.1000107 .

A number of explanations have been proposed for the observed injuries in the animals that stranded in the areas of sonar exercises. These tentative explanations, called hypotheses need to be tested through experiments and checked for consistency in any further observations in order to determine whether they are correct.

Acoustic resonance: One proposed hypothesis was that hemorrhages occurred because air-filled tissues (such as the lungs and head sinuses) resonated when exposed to the sonars, causing blood vessels nearby to rupture. This hypothesis was ultimately found to be unlikely because for resonance-related motion to cause injury, the tissues would need to move large amplitudes . NOAA held a workshop in 2003 to discuss the effects of acoustic resonance in cetaceans (for more information see Report of the Workshop on Acoustic Resonance as a Source of Tissue Trauma in Cetaceans). The workshop concluded that acoustic resonance at the received sound levels and frequencies [20] Finneran, J. J. (2003). Whole-lung resonance in a bottlenose dolphin ( Tursiops truncatus ) and white whale ( Delphinapterus leucas ). The Journal of the Acoustical Society of America, 114(1), 529&ndash535. https://doi.org/10.1121/1.1575747 would have caused tissue movements in the nanometer range, which is far too small to cause injury. Further, key air spaces in the animals examined did not contain hemorrhages. Even more important, because of similarities in lung and sinus structures among toothed whale species, resonance should have damaged most of the species in the vicinity, but only beaked whales stranded.

Decompression Sickness: Another hypothesis that has been proposed to explain the gas bubbles and tissue damage observed in the strandings in the Canary Islands is that the animals experienced decompression sickness (DCS) [21] Jepson, P. D., Arbelo, M., Deaville, R., Patterson, I. A. P., Castro, P., Baker, J. R., &hellip Fernández, A. (2003). Gas-bubble lesions in stranded cetaceans. Nature, 425(6958), 575&ndash576. https://doi.org/10.1038/425575a [22] Fernández, A., Edwards, J. F., Rodríguez, F., de los Monteros, A. E., Herráez, P., Castro, P., &hellip Arbelo, M. (2005). &ldquoGas and fat embolic syndrome&rdquo involving a mass stranding of beaked whales (Family Ziphiidae) exposed to anthropogenic sonar signals. Veterinary Pathology, 42(4), 446&ndash457. https://doi.org/10.1354/vp.42-4-446 . Scientists suggested that beaked whales might have changed their diving pattern in response to the sounds and come to the sea surface faster than normal, causing bubbles to form in their tissues. Some tests have been carried out to determine the probability that this hypothesis is correct. Data from bottlenose dolphins show that rapidly diving animals may accumulate nitrogen in their muscles. The same model of nitrogen accumulation was applied to the diving behavior of the northern bottlenose whale, a beaked whale, and a blue whale, a baleen whale [23] Houser, D. S., Howard, R., & Ridgway, S. (2001). Can diving-induced tissue nitrogen supersaturation increase the chance of acoustically driven bubble growth in marine mammals? Journal of Theoretical Biology, 213(2), 183&ndash195. https://doi.org/10.1006/jtbi.2001.2415 . Their results suggested that in long dives, supersaturation levels as much as 300% might occur. In addition, other studies suggest that if animals stay at the surface longer than normal or otherwise change their diving behavior, they might increase their risk for decompression sickness [24] Tyack, P. L., Johnson, M., Soto, N. A., Sturlese, A., & Madsen, P. T. (2006). Extreme diving of beaked whales. Journal of Experimental Biology, 209(21), 4238&ndash4253. https://doi.org/10.1242/jeb.02505 [25] Fahlman, A., Olszowka, A., Bostrom, B., & Jones, D. R. (2006). Deep diving mammals: Dive behavior and circulatory adjustments contribute to bends avoidance. Respiratory Physiology & Neurobiology, 153(1), 66&ndash77. https://doi.org/10.1016/j.resp.2005.09.014 [26] Zimmer, W. M. X., & Tyack, P. L. (2007). Repetitive shallow dives pose decompression risk in deep-diving beaked whales. Marine Mammal Science, 23(4), 888&ndash925. https://doi.org/10.1111/j.1748-7692.2007.00152.x [27] Hooker, S. K., Baird, R. W., & Fahlman, A. (2009). Could beaked whales get the bends? Respiratory Physiology & Neurobiology, 167(3), 235&ndash246. https://doi.org/10.1016/j.resp.2009.04.023 . However, a study of a trained bottlenose dolphin that completed 10-12 dives to depths of 30, 50, 70, or 100 m showed no indication of gas bubbles or elevated blood nitrogen levels, not supporting the hypothesis that nitrogen accumulates during repetitive dives [28] Houser, D. S., Howard, R., & Ridgway, S. (2001). Can diving-induced tissue nitrogen supersaturation increase the chance of acoustically driven bubble growth in marine mammals? Journal of Theoretical Biology, 213(2), 183&ndash195. https://doi.org/10.1006/jtbi.2001.2415 . This hypothesis is still being debated and more research is needed to evaluate it.

The hypotheses about bubbles in the bodies being related to DCS overlook the fact that bubbles form fairly rapidly in any animal that has recently dived and dies, so bubbles in a body are not sufficient evidence to diagnose DCS. DCS is a complex syndrome with many components that result in the injury or death of the diver. Bubbles are just part, but not all, of that mechanism. The evidence in the stranded animals is not consistent with DCS&rsquos characteristic set of symptoms and its known mechanisms for injury. In many cases the bubbles reported in the whales are too large or are found in the wrong organs for DCS. Even more important, none of these hypotheses explains a key element of the strandings, which are why beaked whales are the one group that strands

The gas bubbles and tissue damage that have been observed could have resulted from many causes, some that are not related to sound [29] National Research Council (U.S.) (Ed.). (2003). Ocean noise and marine mammals. Washington, D.C: National Academies Press. . A recent report has found degeneration in the bones of sperm whale specimens collected over the last 111 years [30] Moore, M. J. (2004). Cumulative sperm whale bone damage and the bends. Science, 306(5705), 2215&ndash2215. https://doi.org/10.1126/science.1105452 . Scientists hypothesized that this degeneration is due to bubble formation associated with DCS unrelated to sound exposure. However, these scientists did not consider the possibility that diseases like arthritis or infections may have caused the abnormal appearance in any of these bones. Thus, the decompression sickness hypothesis has not been fully tested as an explanation for observations in the bones of sperm whales, and is not considered a fully explored or accepted explanation of mass strandings.

Diffusion: Another hypothesis put forth to explain the cause of tissue damage is that sound causes bubbles to form or expand in tissues that are supersaturated with nitrogen. One way this could happen is through a process called rectified diffusion [31] Crum, L. A., & Mao, Y. (1996). Acoustically enhanced bubble growth at low frequencies and its implications for human diver and marine mammal safety. The Journal of the Acoustical Society of America, 99(5), 2898&ndash2907. https://doi.org/10.1121/1.414859 . In this case, sound causes small bubbles, which normally exist in the blood and tissues, to grow larger. It is unlikely that this process caused the tissue damage observed in the Bahamas stranding because the levels of sound exposure required to produce rectified diffusion experimentally are greater than were possible from the sonars by several orders of magnitude. This does not eliminate the possibility that static diffusion occurred, but to date, this mechanism has not been explored or determined to be sufficient to produce tissue damage in marine mammals [32] Houser, D. S., Howard, R., & Ridgway, S. (2001). Can diving-induced tissue nitrogen supersaturation increase the chance of acoustically driven bubble growth in marine mammals? Journal of Theoretical Biology, 213(2), 183&ndash195. https://doi.org/10.1006/jtbi.2001.2415 [33] National Research Council (U.S.) (Ed.). (2003). Ocean noise and marine mammals. Washington, D.C: National Academies Press. [34] Crum, L. A., Bailey, M. R., Guan, J., Hilmo, P. R., Kargl, S. G., Matula, T. J., & Sapozhnikov, O. A. (2005). Monitoring bubble growth in supersaturated blood and tissue ex vivo and the relevance to marine mammal bioeffects. Acoustics Research Letters Online, 6(3), 214&ndash220. https://doi.org/10.1121/1.1930987 .

Environmental Conditions: Research into the acoustic sources and transmission of sound in areas in which the Greece, Bahamas, Madeira, and Canary Island strandings occurred showed three common characteristics [35] D&rsquoSpain, G. L., D&rsquoAmico, A., & Fromm, D. M. (2006). Properties of the underwater sound fields during some well documented beaked whale mass stranding events. Journal of Cetacean Research and Management, 7(3), 223&ndash238. . First, in each location, there is deep water close to land, such as submarine canyons. Second, the sources transmitted series of sound pulses at depths shallower than 10 m (33 ft) while moving at speeds of 2.6 m/s (5.1 kts) or more. Finally, since sound speed is dependent on water depth and temperature, some of the transmitted sound remained near the surface and decreased in level more slowly than would be the case under other conditions. Whether these acoustic characteristics influenced the probability that beaked whales detected the sounds, increased the effects of the sounds through greater propagation, or were not relevant remains unclear. The fact that there are common and relatively unique ocean characteristics in the areas of these five stranding events means that they may be worth considering, and that avoiding exercises in areas that are similar may help reduce the risk of stranding from future naval sonar activity.

Behavioral Response: Another hypothesis suggests that the strandings may have more to do with a number of reactions and sensitivities of this group of animals, such as disturbances in their foraging areas that cause unique behavioral reactions, rather than a direct physical cause related to sound-induced injury from sonar specifically.

Scientists are investigating this hypothesis with a series of studies of the behavioral responses of beaked whales to the playback of certain sounds. The first two phases took place at the Navy&rsquos Atlantic Undersea Test and Evaluation Center (AUTEC) Range off Andros Islands, Bahamas, and the third phase was in the Mediterranean Sea. The AUTEC Range includes several hydrophone s on the seafloor that can detect vocalizing animals. Scientists also went out in small vessels to attach tags to animals in order to record their dives and movements. A total of 16 acoustic tags were attached to individuals of four cetacean species over the three studies. Significant advances in understanding basic diving and vocal behavior were made and nine controlled exposures were conducted using simulated military, mid-frequency sonar sounds, killer whale calls, and &ldquocontrol&rdquo noise . During the AUTEC studies, researchers found that when tagged Blainville&rsquos beaked whales were exposed to all three sounds during deep foraging dives, they stopped echolocating and slowly ascended while moving away from the sound source [36] Tyack, P. L., Zimmer, W. M. X., Moretti, D., Southall, B. L., Claridge, D. E., Durban, J. W., &hellip Boyd, I. L. (2011). Beaked whales respond to simulated and actual navy sonar. PLoS ONE, 6(3), e17009. https://doi.org/10.1371/journal.pone.0017009 . The whales reacted to the killer whale calls at much lower sound levels than they did for the sonar and control noise. However, they did not react to the anthropogenic sounds at the same level as they did for sounds of potentially lethal predators.

The next phase is a five year project off southern California. Additional studies are needed to identify whether these initial observations are generally applicable in other circumstances, and to extend studies to previously untested species such as large baleen whales, seals, and sea lions.

Much more scientific research is needed to understand why a relationship in time and location exists between some beaked whale mass strandings and the use of multiple, mid-frequency sonars in critical areas. At present, we still do not have an answer. Science is an evolving process and future work may help us further understand what we are observing.

The content on DOSITS is based on well understood scientific principles, peer-reviewed literature, and high quality sources of scientific data. Independent experts who specialize in underwater acoustics have reviewed the material in this section.


Do Whales Commit Suicide?

Witnessing any dolphin or whale stranding live is a deeply moving experience particularly when you end up accompanying an individual to the end of its life. My stomach still churns remembering the time that I encountered one in Scotland.

But the reasons behind such events remain mysterious. Dolphins and whales can strand together – most recently, ten long-finned pilot whales became stranded on a beach near Calais, seven of which died – but we can’t pinpoint a single reason why this happens. Instead, many different factors appear to be involved.

Some mass strandings are easy to solve, because the individuals involved are similarly sick or injured. In these cases, they strand because they are pushed inshore by currents as they ail and die. Alternatively, they head for shore because they are simply too sick to swim.

Harmful algal blooms, for example, have been linked to mass strandings of whales as far back as the Miocene. Epizootics – disease events among an animal population – are also a common culprit. A morbillivirus (related to our measles virus) outbreak among dolphins in the North Atlantic caused several mass strandings along the US eastern seaboard in 1987 and 1988.

Even Whales Make Mistakes

Accidents happen, too. Naval exercises, which may involve the use of high-powered sonar, have been linked to mass strandings as individuals become confused, or get injured or injure themselves trying to flee. Like human divers who surface too quickly, some even get the bends (decompression sickness).

There are also long-term trends, which are linked to tougher environmental conditions. Perhaps food stocks are low, temperatures are unusually high or low, or pollutants enter the water. Any of these factors could cause the mammals to behave differently.

Some studies also point to features on the coastline and at sea that might disorient whales and dolphins. Finally, even whales and dolphins make mistakes, as in the below video of a killer whale, filmed earlier this year.

It is also worth remembering that many of these species live in social groups. As in human communities, if an individual is affected by any of the factors above, then others travelling with it will also be exposed to the same problems.

An Ocean Mystery

But illness, injury and error aren’t always behind these events. Far more intriguing, it is not uncommon for some strandings to involve healthy animals, seemingly unaffected by any of these problems.

This is particularly true of pilot whale mass strandings, such as the recent Calais event. This has puzzled biologists for centuries: why would a healthy animal put itself in such danger if there is no reason to? Is it possible that they are deliberately harming themselves? Even attempting suicide?

Pilot whales live in matrilineal societies. They spend their lives in schools that are composed of extended families centred around the females – mothers and their daughters are the family focal points.

Based on this social structure, the common assumption has long been that healthy animals strand themselves as an altruistic gesture, that they do so to continue caring for distressed family members. Recent work, however, casts doubt on this analysis, with genetic tests showing that animals stranded close to each other during mass events may not be related after all. Perhaps this isn’t always a family tragedy.

So Why Strand?

The evolution of whales and dolphins is one of the best documented in the animal kingdom. These species evolved from land-based ancestors and share an ancestry with modern ungulates, think 𠇌ows-with-attitude”.

Their invasion of the sea was progressive, and therefore we are left to ponder whether in difficult times, individuals might still instinctively react as if land confers an element of safety.

Regardless of this, however, if injured or sick, these marine mammals will still be able to rest more easily if they can find a shallow area where they can stop moving. And that places them in hazardous situations.

While there are advantages to fleeing to or resting in shallow water, stranding is a messy business. It leads to further injuries, such as cuts and abrasions, as well as internal injuries caused by the unsupported weight of the body on internal organs – their bodies are designed to swim and float, not bear their mass on land. Often, it will lead to death.

We simply don’t know why some apparently healthy whales and dolphins strand themselves. Which begs the question: are they doing it deliberately?

Whales beached at Farewell Split, South Island, New Zealand

The social caring hypothesis still remains the favoured explanation at this stage: these individuals strand to stay in contact with their sick or injured companions, whether relatives or otherwise. What we don’t fully understand are the mechanisms behind this. These can range from simple ‘hardwired’ instincts to complex behaviours, which may allow them to reflect on the needs of other members of their group, even act altruistically. The truth probably lies somewhere in between.

How We Can Help

Thankfully, we have developed good techniques over the past 25 years to assess best strategies to save as many individuals as possible during a mass stranding. This involves a rapid triage process to know which individuals should be refloated first and the identification of the ‘problem’ individuals – those likely to be at the origin of the stranding.

The truth is that individuals will often re-strand and die hours or days after being refloated – doubtless because they were sick or injured in the first place – but some do get away.

We have learned a lot since Aristotle first wondered why these creatures strand together sometimes – and will never stop trying to help them. Establishing exactly why some of them do it, however, still eludes us.

This article was originally published on The Conversation. Read the original article.


Hearing in Cetaceans: From Natural History to Experimental Biology

T. Aran Mooney , . Brian K. Branstetter , in Advances in Marine Biology , 2012

6.2 Advancements in AEPs

As described above, there are many types of studies which address hearing in odontocetes. However, a large proportion of them now involve AEP measurements ( Fig. 4.4 ). AEP is an appealing method because data can be gathered rapidly with minimal or no animal training investment. A complete audiogram can be obtained in an untrained animal in less than 20 min, enabling hearing tests even during situations where time is severely limited ( Nachtigall et al., 2004, 2005 ). Recording times can be dramatically decreased by simultaneously recording responses to multiple frequencies ( Finneran and Houser, 2007 ) and using automated methods of response detection ( Finneran et al., 2007a ).

One advantage of AEP-related methodology has been to opportunistically measure the hearing of stranded animals, thus broadening the number of individuals and species tested ( Ridgway and Carder, 2001 André et al., 2007 ). Early attempts at recording AEPs from stranded animals were conducted at rehabilitation facilities and produced mixed results ( Ridgway and Carder, 2001 ). The animals tested were large and included a pygmy sperm whale (Kogia breviceps), a grey whale (Eschrichtius robustus) calf, and a neonate sperm whale (Physeter macrocephalus). The response records were somewhat noisy and full audiograms were not acquired, perhaps because the large size of animals reduced signal-to-noise ratios of the AEP ( Szymanski et al., 1999 Houser et al., 2007 ). However, the study produced novel records, showed the efficacy of the technique, and laid substantial groundwork for future research.

Improvements in methods and equipment between 2001 and 2005 led to successful AEP recordings from a stranded neonate Risso's dolphin (G. griseus), producing a full audiogram and an estimate of temporal resolution ( Nachtigall et al., 2005 Mooney et al., 2006 ). This animal had sensitive and broadband hearing, discounting suggestions that there may have been permanent auditory damage due to a potential noise-induced stranding event ( Fig. 4.2 ). However, “profound” hearing loss has been found in other stranded odontocetes including pilot whales, bottlenose dolphins, and rough-toothed dolphins ( Mann et al., 2010 ). The authors speculated that the causes of hearing loss vary and could include congenital defects, chemical contaminants, and normal presbycusis.

A major advance in AEP technology is the development of portable systems which can be applied in field situations ( Ridgway and Carder, 2001 Delory et al., 2007 Taylor et al., 2007 Finneran, 2009 ). The AEP test on the stranded Risso's dolphin involved flying a desktop computer from Hawaii to Portugal and was conducted over 5 days. Since these tests, AEP systems have been reduced in size to laptop-based systems, and audiograms are collected much more rapidly. To date, AEP recordings in the field have been made with catch-and-release procedures on white-beaked dolphins ( Nachtigall et al., 2008 ) and beach-stranded delphinids ( Moore et al., 2011a ), showing promising results despite logistical challenges.

Recently, novel AEP experiments have combined AEPs with morphological studies to address form-and-function questions. Montie et al. (2011) examined the hearing of two stranded pygmy killer whales. They moved electrode locations and created 3D reconstructions of the brain from CT images (Fig. 4.1), while concurrently measuring the amplitude of the ABR waves. Their results provided evidence that the neuroanatomical sources of ABR waves I, IV, and VI were the auditory nerve, inferior colliculus, and the medial geniculate body, respectively. Other studies have combined AEP with CT and MRI to examine the hearing pathways of odontocetes ( Mooney et al., 2011 ). Using a jawphone transducer to present stimuli, Mooney et al. showed that AEP responses can be generated from multiple locations on the head and body. Jawphones placed at the mandibular fat bodies (identified from MRI and CT) tended to produce higher amplitude AEPs, lower thresholds, and faster responses, although this was somewhat frequency dependent ( Fig. 4.3 C). Thus, the head receives and guides sound in multiple ways, confirming earlier findings by Møhl et al. (1999) which mapped the areas of best sensitivity in the bottlenose dolphin head using AEPs and jawphone-presented stimuli. These areas of best sensitivity differ slightly between the few species examined (bottlenose dolphin, beluga, finless porpoise Fig. 4.3 C and D), suggesting that the diverse morphologies found among odontocete species affect how each of them receives sound ( Mooney et al., 2008 ).


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