Subject: pilot whales - why do they strand?

Dagmar Fertl (Dagmar.Fertl@mms.gov)
Tue, 13 Apr 1999 08:29:23 -0400

     From: Susan Burroughs <TJSFB@dnamail.com>
     To: Dagmar_Fertl@mms.gov, pita@whale.wheelock.edu
     Subject: Pilot Whales
     
     Can you please tell me some educated theories on why pilot whales 
     beach
     themselves?
     
     Thank You: )
     Jen S.
     *************************
     Jen,
     
     No one really knows exactly why whales and dolphins strand, but there 
     are a number of ideas as to causes.  Since you specifically mention 
     pilot whales, I imagine you are interested in what causes mass 
     strandings.  Pilot whales are one of the species that seem to be more 
     inclined to mass strand.
        Cetaceans that mass strand very often are offshore animals that 
     have a highly evolved social structure.  This means that for a pilot 
     whale to survive in the wild, they need to be part of a fairly large 
     group of whales.  Sometimes what happens is that once a critical 
     number of the school heads for shore, the rest of the herd is likely 
     to follow.  What causes them to strand to start off?  
        There are a number of possible causes for cetacean strandings, 
     including weather conditions, disease (such as a virus, brain lesion, 
     parasites in the ears), and magnetic field anomalies.  A whale's 
     navigtion (by sonar or other senses) could be confused by shallow 
     sandbanks, magnetic anomalies, or unfamiliar topographic features.  It 
     has been proposed that perhaps some cetaceans use magnetic field 
     detection to navigate (like pigeons or other animals) and areas where 
     strandings often occur might be magnetic field anomalies, places where 
     the earth's magnetic field has a disturbance to it, and the animals 
     get confusing 'map directions'.
        Many times when a mass stranding occurs, and people attempt to get 
     the animals back to sea, they strand again.  We're not really sure why 
     that happens, but maybe they are confused from having been in shallow 
     water or weakened by illness or starvation and find it difficult to 
     come to the water's surface to breathe, and find it easier to be in 
     shallow water.  It oftens happens that the other animals in the group 
     want to 'stand by' a whale or dolphin that is injured, and thus would 
     not want to return to sea without one of their school members.  
     
     Hope I answered your question the way you needed.
     Dagmar