Tuesday, February 22, 2011

Whale and Dolphin Mass Suicide an Unsolved Mystery



There are many theories about why whales and dolphins sometimes swim into shallow water and end up stranding themselves on beaches in various parts of the world.
Some scientists have theorized that a single whale or dolphin may strand itself due to illness or injury, swimming in close to shore to take refuge in shallow water and getting trapped by the changing tide. Because whales are highly social creatures that travel in communities called pods, some mass strandings may occur when healthy whales refuse to abandon a sick or injured pod member and follow them into shallow water.
Mass strandings of dolphins are far less common than mass strandings of whales. And among whales, deep-water species such as pilot whales and sperm whales are more likely to strand themselves on land than whale species such as orcas (killer whales) that live closer to shore.
Some observers have offered a similar theory about whales pursuing prey or foraging too close to shore and getting caught by the tide, but this seems unlikely as a general explanation given the number of stranded whales that have turned up with empty stomachs or in areas devoid of their usual prey.




How do you define a mass stranding?

The definition varies from country to country but it is typically two animals or more unrelated animals (not, say, a mother and a calf) stranding in the same location. The largest stranding of false killer whales on record is 835 animals, but sometimes you see mass strandings involving just a few animals.* There are some species like pilot whales that are notorious for mass strandings. We have records going back to Puritan settlements in New England reporting mass strandings in the same places we see them today. Back then, it was a BBQ instead of a disaster.



Are strandings something we should be worried about?
These are species that are unusual, that are beautiful, and important for the ecology of our seas. If there is an activity humans are doing precipitating these strandings we need to know about it—we need to make decisions about pollutants, shipping noise and sonar. Are we in some way contributing to declining health of critical populations, like the northern right whale?

I have to provide the caveat that strandings we know going back to Aristotle, meaning they may be a natural phenomenon. That raises an interesting question: If you have an animal and it is stranded and you insist on returning it to the sea, are you harming the population? If they are sick or diseased, what are we doing to that population pool? I'm not advocating that we don't rehabilitate animals, if we can. We should understand causes of stranding, but we also have to accept the fact that strandings may be in many cases natural phenomenon.



Are mass strandings on the rise?

That's a really good question. We certainly have more reports over time, and that's something a number of people are looking into. In Cape Cod there's been a slight increase in the last two years. But looking around the world, stranding reports seem to follow human populations. As beach areas become more popular—meaning more people going to beach and more people interested in whales and dolphins—you get more reports. You have to normalize data for increased interest and traffic, and it's not clear whether there are more strandings or just more reports.




Does Navy Sonar Cause Whale Strandings?
One of the most persistent theories about the cause of whale stranding is that something disrupts the whales’ navigation system, causing them to lose their bearings, stray into shallow water, and end up on the beach.
Scientists and government researchers have linked the low-frequency and mid-frequency sonar used by military ships, such as those operated by the U.S. Navy, to several mass strandings as well as other deaths and serious injuries among whales and dolphins. Military sonar sends out intense underwater sonic waves, essentially a very loud sound, that can retain its power across hundreds of miles.
Evidence of how dangerous sonar might be for marine mammals emerged in 2000, when whales of four different species stranded themselves on beaches in the Bahamas after a U.S. Navy battle group used mid-frequency sonar in the area. The Navy initially denied responsibility, but a government investigation concluded that Navy sonar caused the whale strandings.
Many beached whales in strandings associated with sonar also show evidence of physical trauma, including bleeding in their brains, ears and internal tissues. In addition, many whales stranded in areas where sonar is being used have symptoms that in humans would be considered a severe case of decompression sickness, or “the bends,” a condition that afflicts SCUBA divers who resurface too quickly after a deep dive. The implication is that sonar may be affecting the whales’ dive patterns.

Other possible causes put forth for the disruption of whale and dolphin navigation include:
  • rough weather, weakness due to old age or infection, difficulty giving birth, and navigational mistakes , taking in consideration that a single stranded animal (especially if it's the leader) can prompt the entire pod to respond to its distress signals and become stranded, are the most common causes
  • hunting too close to shore and following the preys in shallow waters is another common cause
  • In some cases predators (such as killer whales) have been known to panic whales, herding them towards the shoreline
  • Another proposed cause is that the  echolocation system used by many whales can have difficulty picking up very gently-sloping coastlines.
  • A controversial theory attributes the strange behaviour to radical changes in the  Earth's magnetic field just prior to earthquakes and in the general area of earthquakes.
  • "Follow-me" strandings occur when larger cetaceans follow  dolphins and  porpoises into shallow coastal waters. 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.
Unfortunately it seems that another cause has been added by men the sonar  noise pollution possibly explaining the huge numbers of recent strandings:
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, 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.


Into the Deaths of the Ocean
video



Watch Connie Merigo - Mass Strandings of Dolphins and Whales   Video on PBS   NPR Forum Network
Click HERE


A deeper look into the matter.
First of all, even if the frequency of the beachings has lately been really high, this shoud not deceive us because  cetaceans strandings have always occured in human history as you can see in the following drawings from 1577 and 1598 (enlarge them clicking on it, they are wonderful documents)


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



Stranded whale at Katwijk in Holland in 1598.

and in this picture from 1902 (compare it with THIS picture from one of the strandings a few years ago... the situation seems pretty similar, isn't it?)


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

So, speaking about the causes of these terrible events we should not forget a lot of natural circumstances that have always caused them:


The following are the strandings that hit the news, clicking on the picture or on the title will take you to the corresponding post:


March 2009, Canada, one humpback whale saves itself

Whale caught in crab pots gets stranded but free itself on its own

March 2009 Tasmania, hundred of pilot whales ans a small pod of dolphins
Whales and dolphins stranded together in Tasmania
Whales and dolphins stranded together in Tasmania

February 2009, Philippines, people save hundreds of dolphins
About 200 stranded dolphins rescued in Manila Bay
More than 200 dolphins saved from mass stranding in Manila

January 2009, Tasmania it's the time of a pod of sperm whales
sperm whales stranded
The slow death of a sperm whales pod

December 2008, Tasmania again
150 Pilot whales stranded in Tasmania
It happened again. 150 Pilot whales stranded in the worst mass death in twenty years.

Novemeber 2008, pilot whales in Tasmania
stranded pilot whales
64 pilot whales stranded on Tasmanian beach, 11 has been saved

March 2008, stranding in Senegal
Beached whales in Senegal
A race against time to save 100 beached whales in Senegal

a beached whale in Scotland

The beached whale

No comments:

Post a Comment

coment