Twenty-eight pilot whales strand on West Ruggedy Beach north of Mason Bay, Steward Island, New Zealand

by Captain David Williams

Deafwhale Society, Inc.

(See our prediction at the bottom of this page for a mass stranding on a beach somewhere near Tasmania by the end of February, 2010)

By SAM McKNIGHT - The Southland Times (February 15, 2010)

Twenty-eight pilot whales are dead after a stranding at a remote Stewart Island beach yesterday.

Department of Conservation acting southern islands area manager Mark Townsend said the whales were discovered by a passing tramper about 9am.  The tramper reported the stranding to DOC staff using a satellite phone.  The stranding happened on the remote West Ruggedy Beach, north of Mason Bay.  By the time staff arrived about an hour later by helicopter, they found the whales scattered across a 600m to 700m stretch of the beach.  It was not known how long the whales had been there or why they stranded.  Nine whales were already dead when DOC staff arrived and there was no option but to euthanize the remaining 19, Mr. Townsend said.

DOC biodiversity manager Brent Bevan, who was one of those at the scene, said wild seas and 30-to- 40-knot onshore westerly winds made it impossible to mount a rescue effort to try to save the survivors.  "They were in reasonably good health when we got there but the weather conditions were so bad it would have been far too dangerous to try anything. If there was a chance we could have saved them, we would have given it a go – but not in those conditions," Mr. Bevan said.

Mass strandings are not uncommon on Stewart Island. On 8 January 2003, 159 pilot whales went ashore.

Can the 14 February 2010 stranding be associated with an upstream earthquake? 

Can the 8 January 2003 standing also be associated with an upstream earthquake?

The answer to both questions is yes... these two stranding were both preceded by shallow-focused earthquakes.  They also have one other thing in common--rough seas. 

On 5 February 2010, at 10:48 PM local time a magnitude 5.1 earthquake erupted in the seabed one mile off the coast of South Island (location 44.783S 167.375E).  The event was hypocentered 5 km below the ocean's surface (air/water interface). 

References: USGS  New Zealand GeoNet

Regardless of exactly how earthquakes in the seabed generate rapid pressure changes in the water, the net results is that the air contained in the head sinuses of each diving whale expands and contracts 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 are no longer able able to dive and feed themselves due to severe pain and loss of echo-location abilities.  Nor are they able to echo-navigate.   Bottom line, the pod quickly became lost and no longer able to care for themselves.  Not having a sense direction, the pod huddled together for protection against sharks, and just starting swimming off in a random direction.  This random swim path is quickly corrected by the surface currents which direct the animals downstream in the path of least resistance.

The shallow depth of the above earthquake is of major importance in determining the potential for harm to diving whales because the nearer the hypocenter (focal point) is to the seabed, the less opportunity the energy has to spread out and dissipate before it arrives at the rock/water interface.  Said differently, the less distance the seismic waves must travel from the focal point to the rocky bottom, the more energy will enter the water, the more potent will be the alternating pressure changes, the more dangerous the event will be to marine mammals, turtles, and fishes with swim bladders.  For example, all things being equal, a magnitude 3 event focused only 2 km below the rock/water interface is likely as dangerous as a magnitude 6 event focused at 20 km. 

In many cases the focal depth is restricted to some chosen depth. This is most commonly done for crustal earthquakes. Unless there is a station within 25 km of a shock in the upper crust, or within 50 km of a shock in the lower crust, a nominal depth of either 10 or 33 km is usually assigned, according to the crustal phases present and the goodness of fit of the resulting solution. Less often, the depth is restricted to a smaller value, particularly when the strengths of locally reported felt intensities indicate an uncommonly shallow focus. In other words, depth of focus is often an arbitrary assignment, especially at sea a thousand kilometers from the nearest instrument.

Twenty-eight pilot whales went ashore on Stewart Island ~200 miles downstream from the epicenter of the above quake ten days later.  They were directed from the epicenter to the beach by the Southland Current that flows in an easterly direction around the southern tip of South Island between Stewart Island and the mainland.  After only ten days at sea, the pod should have been able to see the shallow water and avoid the beach.  However, with the rough seas, the water was likely filed with millions of bubbles and lots of sand reducing visual contact with the bottom to less than a few feet.  The heavy seas drove the whales ashore several weeks before they would have normally stranded.  had they not stranded on Stewart Island, they might have beached on Banks Peninsular or at Chatham Island. 

The same thing happened on 8 January 2003 when 159 long-finned pilot whales were reported to have live-stranded on a sandy beach at the Old Sand Neck on Stewart Island, New Zealand (46° 58’ S, 168° 11’ E) not far from Half Moon Bay. The whales were lying on the high tide line, suggesting that the stranding happened around 6:30 in the morning. About 60% of the whales were already dead by the time a rescue team from the Department of Conservation (DoC) arrived on site, around midday. Deaths were thought to be mainly due to overheating. A total of 37 whales were refloated and herded out to sea. The re-floating effort was apparently a success with no sign of restranding on the following days (although two whales, with healing skin damage, live stranded at a different location of the island on January 25). 

This stranding was associated with a swarm of 17 shallow earthquakes in about the same area as the 5 February 2010 event.

Starting on 22 December 2002 and ending 7 days later, a swarm of seventeen (17) extremely shallow focused earthquakes (5 km) occurred one after the other as shown in the map on the right. These quakes ranged from 4.6 to 3.7 magnitude.

Normally, we exclude earthquakes <4.5 magnitude when the hypocenter is 10 kilometers or greater.  On the other hand, we believe that a magnitude 3.5 event is capable of inducing injury in whales when the depth of the hypocenter is <5 kilometers. (The depth of the hypocenter of an earthquake at sea is measured from the ocean's surface (air/water interface).

Swarms of earthquakes show up consistently in our search for a likely candidate.

To verify these events go to: GeoNet Quake Search

The earthquakes responsible for the 2003 mass stranding as retrieved from GeoNet are listed below:

SPECIAL STRANDING PREDICTION:

There is a fair chance that the earthquake listed below might have injured a pod of whales.  If so, our best guess is that this pod might strand near Tasmania by the end of February.  There is also a chance the pod might bypass Tasmania to strand somewhere at the Southern tip of South Island New Zealand around the 10th of March, 2010. 

6.1 Mw - SOUTHEAST INDIAN RIDGE