Ninety-two short-fin pilot whales strand on 20 June 2010 in the Cape Verde Islands. 50 whales were beached on Coqueiro beach, Santiago Island, and another 42 on the Sal Island coast.

http://www.rte.ie/news/2010/0622/whales.html

by Captain David Williams

Deafwhale Society, Inc.

Here's another prime example of a seaquake-injured pod of whales running aground. 

On 25 May 2010 (epicenter time 8:09 am) a magnitude Mw 6.3  earthquake (hypo-centered between 3 to 10 km below the ocean's surface) erupted along the NORTHERN MID-ATLANTIC RIDGE at 35.41 N ; 35.97 W.

 http://www.emsc-csem.org/Earthquake/earthquake.php?id=170323#scientific

The movement during the earthquake was predominately side-to-side motion and would not have disturbed the water column excessively if the event had occurred on a flat seafloor.  But the area around the epicenter is not flat.  The motion during the earthquake likely shifted the nearby mountains from side to side converting their slope into the faceplate of a gigantic transducer and causing the surrounding water pressure to suddenly increase and decrease several hundred pounds per square inch every second or so for ~30 seconds. 

Regardless of exactly how the rapid pressure changes came about, the net results was that the air contained in the head sinuses of each diving whale expanded and contracted too excessively, resulting in a barotraumatic injury in the pertygoid sinuses that are so important for proper function of bioacoustics.  The whales survived the earthquake but were no longer able able to dive and feed themselves due to severe pain and loss of echo-location abilities.  Nor were they able to echo-navigate.   Bottom line, the pod quickly became lost and were no longer able to care for themselves.  Not having a sense direction, the pod huddled together for protection against sharks, and just starting swimming in a random direction.

More likely than not, the pod had previously been injured by several undersea earthquakes in the past and had recovered; however, the seaquake waves from this particular quake were just a bit too powerful or the pod was caught is shallow water (under 100 meters) where the percentage of volume change of the air in the sinuses would be much greater than at deeper depths due to reduced ambient pressure.

After the quake, the pod swam off in a downstream direction.   When any animal, including man, swims in a current without a sense of direction, the resistance presented by the flowing water controls the direction which they swim.  It's a matter of physics.  Anything and everything moving through a current without a sense of direction will be turned downstream in the path of least resistance.  It's ten times easier to swim with the flow than against it. 

Surface currents in the area at the time of the earthquake were flowing in a general eastward direction toward Casablanca Morocco and the Straits of Gibraltar.

About a hundred miles before reaching Casablanca, the surface currents begin to shift southward and run along the shoreline of Morocco in a straight path toward the Canary Islands and then onto the Cape Verde Islands.

The trip from the epicenter to the beach was ~2600 mile and took 27 days meaning the pod likely travel downstream about 100 miles per day. 

The point here is to show the process of selecting which earthquake might have caused a particular stranding.

Capt. David Williams

(telephone inquiry should be directed to our Florida landline: 954-306-1549)