125 pilot whales strand in a sand trap on Farewell Spit.

by Captain David Williams

Deafwhale Society, Inc.

 Did a seaquake injure the pod of pilot whales that stranded on Farewell Spit Beach, South Island, New Zealand (link) on 26 December 2009?

 Over 100 stranded whales were discovered at Farewell Spit on the north end of  South Island by the pilot of a tourist plane.   Only 30 were alive when conservation workers arrived.

"They were in bad shape. By the time we got there two-thirds of them had already died. We had to euthanize the rest.  It was horrible but nothing could have been done to save them. It was the most humane thing to do," said department of conservation worker Hans Stoffregen.

"It has been quite hot and they were very distressed. You could see the pain and suffering in their eyes," he said, explaining that the whales had missed several tides and been out of the water for a long time.

The SEAQUAKE THEORY  indicates that sudden changes in ambient pressure (seaquake) generated above the epicenter of certain shallow focus earthquakes in the seabed causes barotrauma in the pterygoid sinuses of the adult pod members. 

Functional biosonar depends on healthy pterygoid air sacs.  Echo-navigation is ineffective if blood and/or body fluid leak into the pterygoid sinuses or if these air sacs collapse due to over expansion during sudden and excessive changes in the surround water pressures.  

When swimming without a sense of direction, the streamline shape of the whale's body, with its fins and broad tail, acts as a wind vane/rudder, constantly steering the animal downstream in the path of least resistance.

At first, seaquake-injured whales can see the shallow water and avoid stranding during daylight and darkness.  But the visual ability to avoid the shallows at night usually fails after 3 to 4 weeks without food and fresh water. After reaching a certain "point of no return,"  the injured pod losses its ability to avoid the beach, usually stranding at night. 

This pod may survive up to 60 days and could easily travel 3,000 miles downstream.  Or, they might travel only a few hundred miles downstream,  swimming around in circles caught inside an eddy of current.

Certain sandy peninsulas several thousand miles downstream from large populations of the species in question that extend out to sea opposing the flow of the current (Farewell Spit, Golden Bay, Cape Cod Bay, and Cape Sorell) serve as catching-arm systems for the seaquake injured pod.  These areas are the world's most popular stranding beaches.  The seasonality of strandings is due to:  (a) a seasonal increase in upstream earthquake activity, seasonal changes in ocean circulation, and seasonal migration of the pods in and out of earthquake-prone areas.  

To see the various current eddies in the Tasman Sea click on  Marine-Remote Sensing-Ocean Currents and select the dates of interest.

The usually current (without considering eddies) flows as follows:

Based on past experience, we have assumed the injurious earthquake was located between 40S and 55S and between 120E to 180E.  We also assumed that the injurious event occurred between October 28 and December 10, 2009.

We searched the ANSS Catalog, which reveals the following four possible events.

Our search parameters were:

• catalog=ANSS

• start_time=2009/10/28,00:00:00

• end_time=2009/12/10,00:00:00

• minimum_latitude=-55

• maximum_latitude=-30

• minimum_longitude=90

• maximum_longitude=170

• minimum_magnitude=4.5

• maximum_magnitude=8

• minimum_depth=0

• maximum_depth=10

• event_type=A

• include events with no magnitude

Date       Time             Lat       Lon  Depth   Mag Magt  Nst Gap  Clo  RMS  SRC   Event ID
----------------------------------------------------------------------------------------------
2009/11/05 09:43:20.71 -52.2920  160.7030  10.00  6.00   Mw   80          1.13  NEI 200911051023
2009/11/28 17:40:26.50 -49.7720  126.5740  10.00  4.70   Mb   21          1.87  NEI 200911281034
2009/12/05 06:03:36.34 -51.4910  139.2070  10.00  4.90   Mb   16          1.03  NEI 200912051006
2009/12/05 06:30:01.39 -51.5210  139.4970  10.00  4.70   Mb   18          0.68  NEI 200912051007

The most suspicious event for the stranding on Farewell Spit is the Magnitude 6 Mw earthquake on November 5, 2009.  When measured from the seismic station on Tasmania (vertical channel -- filtered -- long period 0.05 --  0.08) this quake is shown to emit a rather large portion of its energy as low frequency vibrations with a very strong peak one minute into the disturbance.  (The LF component is hypothesized to more likely cause barotrauma in diving whales.)

MACQUARIE ISLAND REGION (Global CMT Catalog Search 200911050943A)

  Date: 2009/11/ 5   Centroid Time:  9:43:25.5 GMT
  Lat= -52.22  Lon= 160.36
  Depth= 22.8   Half duration= 2.4
  Centroid time minus hypocenter time:  4.5
  Moment Tensor: Expo=25  0.113 0.955 -1.070 -0.237 0.117 0.619 
  Mw = 6.0    mb = 5.3    Ms = 5.3   Scalar Moment = 1.22e+25
  Fault plane:  strike=209    dip=77   slip=178
  Fault plane:  strike=300    dip=88   slip=13

The main drawback for the 5 November event is the relative short distance (1,100 miles) from the epicenter to the standing beach when compared to the 51 days between the quake and the stranding.  Normally when there is ~51 days between an event and the beaching, we find the stranding site to be ~3,000+ miles downstream from the suspicious epicenter.  The only way to justify only 1,100 miles downstream with the 51 days spent at sea is if the pod had been swimming around in a circle for a month or so, caught in one of the many eddies that form in the Tasman Sea.  (To visualize these eddies, go to Marine-Remote Sensing-Ocean Currents and select the dates of interest.)

But even in the presence of many eddies, we're still not sure.  We also like the 4.9 Mb quake on December 5 with the 4.7 Mb aftershock 30 minutes later.  The suspicion here is that any injurious encounter followed 30 minutes later with a second injurious encounter might be more dangerous that a single exposure. 

2009/12/05 06:03:36.34 -51.4910  139.2070  10.00  4.90   Mb   16          1.03  NEI 200912051006
2009/12/05 06:30:01.39 -51.5210  139.4970  10.00  4.70   Mb   18          0.68  NEI 200912051007

In addition, the distance downstream from epicenter to the beach (~1,800 miles) fits better with the 21 days between the event and the beaching.  The only thing that don't fit is that the condition of the pod was very poor when found.  However, if this poor condition can be accounted for by spending several days in hot sun, then the two earthquakes on December 5 fits better with previous observed strandings.  The area is also a likely feeding ground due to the 4-5 seamounts near 51.50S by 139.30E.  The flat-top volcanic mountains rise to within 1,500 meters of the surface.

Said differently, the main reason we are drawn to the 5 November event is due to the poor condition of the pod when discovered.    

Comparing the same parameters of the November 5th event with the December 5th event makes it even more difficult to pick between the two: