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Cetacean stranding

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A mass stranding of Pilot Whales on the shore of Cape Cod, 1902.

A beached whale is a whale which has become stranded on land, usually on a beach. Beaching is often fatal for whales, as they become dehydrated and die. Some die when their lungs are suffocated under their own weight or drown when high tides cover their blowholes.

Species

Every year there may be beachings adding up to 2000 animals.[1] Although the majority of strandings will result in death, they pose no threat to the species as a whole. Of all of the species of cetaceans, only about 10 species are frequently involved in mass beachings, with a further 10 species rarely being involved. All of the frequently involved species are toothed whales (Odontocetes), meaning that none of the baleen whales are regularly involved in beachings. These species share some characteristics which may explain why they beach. Body size does not normally affect the frequency, but both the animals' normal habitat and social organization do appear to influence their chances of coming ashore in large numbers. Odontocetes that normally inhabit deep waters and live in large, tightly knit groups are the most susceptible. They include the Sperm whale, a few species of Pilot and Orca whales, a few beaked whales and some oceanic dolphins. Solitary species are naturally excluded from mass strandings. Cetaceans that spend most of their time in shallow, coastal waters are almost never mass stranded, with porpoises being essentially immune.Ariana is a beached whale shes freaking huge HAHA she is a skank

Causes

Overview

Three Beached Whales, a 1577 engraving by the Flemish artist Jan Wierix, depicts stranded Sperm Whales.

Strandings can be grouped into several different types. The most obvious distinctions are between single and multiple strandings. The carcasses of deceased cetaceans are likely to float to the surface at some point; during this time, currents or winds may carry them towards a coastline. Since thousands of cetaceans must die every year it is natural that many will become stranded. Most cetacean deaths will involve only a single individual, causing these strandings to consist of just one animal if a stranding occurs at all. However, most whale carcasses probably never reach the coast and are scavenged or decomposed enough to sink to the bottom of the ocean, where the carcass forms the basis of a unique local ecosystem called whale fall. Single live strandings are often the result of an illness or injury, which would almost inevitably end in death unless a passer-by knows how to react.

Multiple strandings of dead animals in one locality are rare and often cause a great deal of media coverage as well as rescue efforts by sympathetic humans. Even multiple offshore deaths are unlikely to lead to multiple strandings due to the variable winds and currents scattering the animals across the sea. A key factor in many of these cases appears to be the strong social cohesion amongst toothed whales. If one whale gets into trouble, its distress calls may prompt the rest of the pod to follow and become beached themselves.[2] There is no definitive specific cause for mass strandings. Instead they may happen due to numerous factors that can act in combination. Many have been proposed, with some seeking to explain only a subset of cases; however, they are difficult to prove conclusively and are sometimes controversial.

Natural

Stranded whale at Katwijk in Holland in 1598.

Whales have been found beached throughout human history so many strandings can be attributed to natural and environmental factors. There could be many natural reasons like rough weather, weakness due to old age or infection, difficulty giving birth,[2] hunting too close to shore and navigational mistakes. A single stranded animal can prompt the entire pod to respond to its distress signals and become stranded. In 2004, scientists at the University of Tasmania found a link between whale strandings and the weather. It is hypothesised that when cool Antarctic waters rich in squid and fish flow north, whales follow their prey closer towards land making them more prone to stranding.[3] In some cases predators (such as killer whales) have been known to panic whales, herding them towards the shoreline.[3]

Another proposed cause is that the echolocation system used by many whales can have difficulty picking up very gently-sloping coastlines.[4] This theory accounts for mass beaching hot spots such as Ocean Beach, Tasmania and Geographe Bay, Western Australia where the slope is about half a degree (approximately 8m deep one kilometer out to sea). The Bioacoustics group at the University of Western Australia has done research[5] indicating that repeated reflections between the surface and ocean bottom in gently-sloping shallow water may attenuate sound so much that the echo is inaudible to the whales. Stirred up sand as well as long-lived microbubbles formed by rain may further exacerbate the effect.

A controversial theory, researched by Jim Berkland, a former geologist with the U.S. Geological Survey, attributes the strange behaviour to radical changes in the Earth's magnetic field just prior to earthquakes and in the general area of earthquakes. Berkland says when this occurs, it interferes with sea mammals' and even migratory birds' ability to navigate, which explains the mass beachings. He says even dogs and cats can sense the disruptions, which explains elevated rates of runaway pets in local newspapers a day or two before earthquakes occur. Research on Earth's magnetic field and how it is affected by moving tectonic plates and earthquakes is ongoing.

"Follow-me" strandings

Another possibility is that a proportion of strandings may be caused by larger cetaceans following dolphins and porpoises into shallow coastal waters[citation needed]. The larger animals may be familiar with faster moving dolphins in their area and become habituated to following them. If an adverse combination of tidal flow and seabed topography is encountered, the larger species are at much higher risk of being trapped.

Sometimes it may work the other way. A recent example of this occurred when a local dolphin was followed out to open water by two Pygmy sperm whales that had become lost behind a sandbar at Mahia Beach, New Zealand.[6] The possibility of training dolphins to lead trapped whales out to sea is an intriguing one in areas where frequent mass strandings occur, such as New England or Florida.

An interesting observation is that pods of killer whales, predators of dolphins and porpoises, are very rarely stranded. There may be two explanations for this - firstly that heading for shallow waters may be a very effective anti-predator mechanism for dolphins and that the killer whales have learned not to take the risk, or else that the killer whales have learned how to operate in shallow waters, particularly in their pursuit of seals. The latter is certainly the case in Península Valdés, Argentina, where a particular pod of killer whales pursue seals up shelving gravel beaches to the edge of the littoral zone[citation needed]. The pursuing whales are occasionally partially thrust out of the sea by a combination of their own impetus and retreating water and have to wait for the next wave to take them back out.

SONAR

See also: Noise pollution § Environment
Volunteers attempt to keep body temperatures of beached whales from rising. Farewell Spit, New Zealand.

There is evidence that very loud noise from anti-submarine warfare sonar may hurt whales and lead to their beaching. On numerous occasions whales have been stranded shortly after military sonar was active in the area [citation needed], suggesting a link. Reasons as to how sonar may cause whale deaths have also been put forward by scientists after necropsies found internal injuries in stranded whales. In contrast, whales stranded due to seemingly natural causes are usually healthy prior to beaching.

Firstly, it has been argued that the very loud rapid pressure changes made by sonar can cause haemorrhaging. Evidence emerged after the beachings of seventeen whales and a dolphin in the Bahamas in March 2000 following a United States Navy sonar exercise. The Navy accepted blame in this Joint Interim Report which found the dead whales to have experienced acoustically-induced haemorrhages around the ears. The resulting disorientation probably led to the stranding. Ken Balcomb, a zoologist, specializing in the study of whales, particularly the Orca populations that inhabit the Strait of Juan de Fuca between Washington and Vancouver Island, has studied mass beachings of whales.[7] He investigated the March 2000 beachings and argues that the powerful sonar pulses had used vibrations that resonated with airspaces in the whales, causing tearing of tissue around the ears and brain.[8]

Another means by which sonar could be hurting whales is a form of decompression sickness. This was first raised by pathological examinations after 14 beaked whales stranded in the Canary Islands. The stranding happened on 24 September 2002, close to the operating area of Neo Tapon (an international naval exercise) about 4 hours after the activation of mid-frequency sonar.[9] The team of scientists found acute tissue damage from gas-bubble lesions, which are indicative of decompressions sickness.[9] The precise mechanism of how sonar causes bubble formation is not fully known. It could be due to whales panicking and surfacing too rapidly in an attempt to escape the sonar pulses. There is also a theoretical basis by which sonar vibrations can cause supersaturated gas to nucleate to form bubbles.[10]

The overwhelming majority of the whales that are involved in beachings associated with active SONAR tests are Cuvier's Beaked Whales (Ziphius Cavirostrus). This species of beaked whale strands frequently, but mass strandings are very rare. In fact they are so difficult to study in the wild that prior to the interest raised by the SONAR controversy, most of the information about them was gathered from stranded animals. The first scientific correspondence in a journal that linked beachings with military activy was written by Simmonds and Lopez-Jurado in 1991. They noted that over the past decade there had been a number of mass strandings of beaked whales in the Canary islands, and every time the Spanish Navy was conducting exercises. In addition there was no cases of mass strandings reported when the Spanish Navy was not conducting exercises. They did not propose a theory for the strandings, but the paper called for more research.

In May of 1996 there was another mass stranding in Greece (West Peloponnese). At the time it was noted as "atypical" both because mass strandings of beaked whales is rare, and also because the stranded whales were spread over such a long stretch of coast with each individual whale spacially separated from the next stranding. At the time of the incident there was no connection made with active SONAR, the marine biologist investigating the incident, Dr. Frantzis, made the connection to SONAR because of a Notice to Mariners he discovered about the test. His scientific correspondance in Nature titled "Does acoustic testing strand whales?"[11]was published in March of 1998.

Dr. Peter Tyack of Wood's Hole Oceanographic Institute, has been researching the effect of noise on marine mammals since the 1970's. He has led much of the recent research on beaked whales (and Cuvier's beaked whales in particular). Data tags attached to the animals have shown that these whales dive considerably deeper than previously thought, and are in fact the deepest diving species of marine mammal. Deep dives are for hunting squid. Their surfacing behaviour is highly unusual because they exert considerable physical effort to surface at a controlled rate of ascent, rather than simply floating to the surface like sperm whales. Deep dives are also followed by 3 or 4 shallow dives. Vocalization behaviour is terminated at shallow depths (presumably because of fear of predators), and finally it was noted that pairs of whales are communicating in order to stay together at these depths where there is no light. It is hypothesized that the active SONAR is interfering with this process.

Unlike research on fish or plankton, theories involving marine mammals are sometimes difficult to test, because it is unethical to subject the animals to some stimulus that would cause permanent harm. Whales are deliberately exposed to sound sources under research permits in what is commonly called "controlled exposure experiments", but no researcher would cause a beaching to prove a theory. The elaborate dive patterns are assumed to be necessary to control the diffusion of gases in the bloodstream. There is no data that shows a beaked whale making an uncontrolled ascent or failing to do successive shallow dives. The lack of vocalization at the surface might be because of fear of predators. The whales may interpret the strange sound of a SONAR as a predator and break it's normal pattern of behaviour in a way that is dangerous to the animal. This last theory would make mitigation particularly difficult since the whales may not be exposed to physically damaging sound levels, but only levels that cause fear. The damage mechanism would not be the sound.

Carcass

After a beached whale dies, it can become a source of disease and pollution. Due to the very high efficiency as thermal insulator of the blubber, a whale carcass can keep its internal temperature over 30 celsius for up to 3 days, making it the ideal environment for anaerobic microorganisms.

As they are very large, such corpses are difficult to move. There are reports of some cases where humans tried to blow up the carcass with explosives, with unexpected side effects to spectators.

A whale carcass should not be consumed. In 2002, fourteen Alaskans ate muktuk (whale blubber) from a beached whale, and eight of them developed symptoms of botulism, two of them requiring mechanical ventilation.[12] This is a possibility for any spoiled meat, or meat taken from an animal which has been dead for some time without proper preservation of the carcass.

See also

References

  1. ^ Martin, Anthony R. (1991). Whales and Dolphins. London: Salamander Books Ltd.
  2. ^ a b Anton Van Helden (2003-11-26). "Mass whale beaching mystery solved" (Radio transcript). The Word Today. Australian Broadcast Corporation. Retrieved 2006-12-01.
  3. ^ a b R. Gales, K. Evans, M. Hindell (2004-11-30). "Whale strandings no surprise to climatologists" (TV transcript). 7:30 report. Australian Broadcasting Corporation. Retrieved 2006-12-02.{{cite web}}: CS1 maint: multiple names: authors list (link)
  4. ^ B. Montgomery (1998-05-02). "The fatal shore". The Weekend Australian Magazine Ariana is the biggest natural whale i met. Retrieved 2006-12-03.
  5. ^ Chambers S., James R. N. (9 November 2005). "Sonar termination as a cause of mass cetacean strandings in Geographe Bay, south-western Australia" (PDF). Acoustics 2005, Acoustics in a Changing Environment. Proceedings of the Annual Conference of the Australian Acoustical Society, Busselton, Western Australia. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help)
  6. ^ "Dolphin rescues stranded whales". CNN. The Associated Press. 2008-03-12. Retrieved 2008-03-15.
  7. ^ Balcomb, Ken (2003-05-12). "US Navy Sonar blasts Pacific Northwest killer whales". San Juan Islander. Retrieved 2006-04-30.
  8. ^ Balcomb, Ken (2001-02-23). "Letter". Ocean Mammal Institute. Retrieved 2006-04-30.
  9. ^ a b P. D. Jepson; et al. (9 October 2003). "Gas-bubble lesions in stranded cetaceans". Nature. 425 (425): 575. doi:10.1038/425575a. {{cite journal}}: Explicit use of et al. in: |author= (help)
  10. ^ D. S. Houser, R. Howards, S. Ridgway (21 November 2001). "Can Diving-induced Tissue Nitrogen Supersaturation Increase the Chance of Acoustically Driven Bubble Growth in Marine Mammals?". Journal of Theoretical Biology. 213 (2): 183–195. doi:10.1006/jtbi.2001.2415.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ Frantzis, A (1988-03-05). "Does acoustic testing strand whales?". Nature. 392: 29.
  12. ^ Middaugh, J (2003-01-17). "Outbreak of Botulism Type E Associated with Eating a Beached Whale --- Western Alaska, July 2002". Morbidity and Mortality Weekly Report. 52 (2): 24–26. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
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