Beached whale
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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. Humans sometimes try to save beached whales; however, such efforts are not always successful.
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[edit] 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 rarely being involved. All of these species are toothed whales, 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 organisation do appear to influence its 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 Killer 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.
[edit] Causes
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 which occur naturally will only involve a single individual, causing these strandings to consist of just one animal, if a stranding occurs at all. However, most carcasses never reach the coast and are scavenged or decomposed enough to sink to the bottom of the oceans. 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.
[edit] Natural causes
Whales have been found beached throughout human history so many strandings can be attributed to natural and environmental factors. There could be all sorts of natural reasons such as rough weather, weakness due to old age or infection, difficulty giving birth[2], hunting too close to shore and making 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 theorised 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 hotspots 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 behavior 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 prior to earthquakes. Research on Earth's magnetic field and how it is affected by moving tectonic plates and earthquakes is ongoing.
[edit] Human-made causes
There is some evidence that anti-submarine warfare sonar and other underwater noises (such as those emitted from oil drills) are of a sufficient intensity to cause the whales to surface too rapidly. The whales suffer hemorrhaging and decompression sickness due to the rapid pressure change. The resulting disorientation could then cause the whale to become beached. Ken Balcomb, a zoologist, specializing in the study of whales, particularly the orca (killer whale) populations that inhabit the Strait of Juan de Fuca between Washington and Vancouver Island, has investigated mass beachings of whales[6]. In March 2000, he investigated a mass beaching of beaked whales in his study population stranded near his Bahamas field station following a U.S. Navy sonar exercise[7]. The four carcasses he examined had haemorrhages in the acoustic regions, and provided the first evidence of pressure traumas that can be "caused" by sonar, although the precise mechanism for damage is still unknown.
Strandings may be caused by poisoning, as happened in 1987-88 to bottlenose dolphins off the northeastern coast of the United States.
[edit] Carcass
After a beached whale dies, it can become a source of disease and pollution. 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[8]. This is of course 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.
[edit] See also
[edit] References
- ^ Martin, Anthony R. (1991). Whales and Dolphins. London: Salamander Books Ltd..
- ^ a b Anton Van Helden (26 November 2003). Mass whale beaching mystery solved (Radio transcript). The Word Today. Australian Broadcast Corporation. Retrieved on 2006-12-01.
- ^ a b R. Gales, K. Evans, M. Hindell (30 Nov 2004). Whale strandings no surprise to climatologists (TV transcript). 7:30 report. Australian Broadcasting Corporation. Retrieved on 2006-12-02.
- ^ B. Montgomery (2 May 1998). The fatal shore. The Weekend Australian Magazine. Retrieved on 2006-12-03.
- ^ Chambers S., James R. N. (9 November 2005). "Sonar termination as a cause of mass cetacean strandings in Geographe Bay, south-western Australia". Acoustics 2005, Acoustics in a Changing Environment. Proceedings of the Annual Conference of the Australian Acoustical Society, Busselton, Western Australia.
- ^ Balcomb, Ken (2003-05-12). US Navy Sonar blasts Pacific Northwest killer whales. San Juan Islander. Retrieved on 2006-04-30.
- ^ Balcomb, Ken (2001-02-23). Letter. Ocean Mammal Institute. Retrieved on 2006-04-30.
- ^ Middaugh, J, Funk, B, Jilly, B, Maslanka, S, McLaughlin 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.
[edit] External links
- Protecting Whales from Dangerous Sonar (Natural Resources Defense Council)
- Does Sonar Harm Whales? (Tasmanian whale stranding October 2005: Epoch Times)
- Sensors and sensibility: navies factor mammals into sonar use Jane's Navy International, 25 August 2006
