On February 04, 2011, eighty-four whales stranded at Puponga Point in Golden Bay, near the base of Farewell Spit, 14 of which died.
The rest refloated on the high tide about midnight and split into two groups; one group headed out to sea but the other had been trying to restrand at Nelson all day. The 70 whales that refloated overnight beached themselves again. Forty at Farewell Spit. Another group of 25 whales are also beached just south of Puponga Point.
Volunteers and members of the public had worked throughout the day to avert a restranding, and had been successful a couple of times. Tactics included standing in the water to form a barrier to the beach.
Advertisement
THE REAL REASON THE POD STRANDED:
The real cause of the stranding was barotraumatic injury to the head sinuses caused by rapid and excessive changes in ambient pressure generated in the water column (seaquakes) above the epicenter of two earthquakes that occurred along the WESTERN INDIAN-ANTARCTIC RIDGE on 28 December 2010 about 1075 km (668 miles) SSW (212 degrees) of Hobart, Australia. The local time in Hobart was 02:27 AM.
The magnitude of the first event was 5.0 Mb, located by computer at 10 km below the rock water interface near 50.832S 139.173E. This area is a popular squid feeding grounds for pilot whales.
The real cause of the stranding was barotraumatic injury to the head sinuses caused by rapid and excessive changes in ambient pressure generated in the water column (seaquakes) above the epicenter of two earthquakes that occurred along the WESTERN INDIAN-ANTARCTIC RIDGE on 28 December 2010 about 1075 km (668 miles) SSW (212 degrees) of Hobart, Australia. The local time in Hobart was 02:27 AM.
The magnitude of the first event was 5.0 Mb, located by computer at 10 km below the rock water interface near 50.832S 139.173E. This area is a popular squid feeding grounds for pilot whales.
Examine a satellite map of the earthquake's epicenter and zoom out to also see the stranding area:
The second event, at 5.6 Mw magnitude and only 2 km deep in the seafloor, was far more dangerous to the pod and likely was the most damaging. It occur in the same area 90 minutes later.
http://www.emsc-csem.org/Earthquake/earthquake.php?id=204741#summary
The seaquake waves (rapid and excessive pressure changes) caused the volume of air in various sinuses to expand and contract rapidly. The changes in the surrounding water pressure was too excessive and rapid. The pressure waves were more potent than the abilities of the whales to adjust. The results of excessive pressure changes in the surrounding pressure is similar to what would happen in a high-flying airliner that suddenly lost cabin pressure. In other words, the entire pod of whales suffered a barotraumatic injury in their massive head sinuses. When these sinus membranes (especially those of the pytergoid sinuses) tear or rupture, the cavities that normally contain air, fill up with blood and body fluids and are no longer functional.
The elaborate head sinuses of mass stranders not only serve in the generation of sonar clicks, they also serve to isolate each cochlea from unwanted sound. Cochlea isolation is a critical process and at the very heart of echolocation. In other words, the rapid and excessive changes in water pressure causes an equal and rapid change in the volume of air contained in the head sinuses of a diving whales. A break or tear in these sinuses from over-expansion allows blood and body fluids to fill the sinus rather than air. Without air-filed sinuses, the biosonar of each whale simply fails to function.. A busted sinus would also prevent diving and feeding.
The whales can recover if the injury is not too severe and they find food on the surface; however, if recovery does not happen within a few weeks, the pod will reach a point of no return when recovery is impossible.
As mentioned above, the pod losses its ability to navigate when its sinuses are not working properly. Without a sense of direction, the wounded animals will huddle together for protection against shark attack and swam off from the epicenter of the earthquake in the direction of the flow of the surface currents.
The resistance in the water to swimming in any direction other than downstream prevents the non-navigating whales from heading upstream or even parallel to the flow. The path of least resistance for injured whales is ALWAYS DOWNSTREAM with the flow of the current.
One can easily verify this simple fact by closing your eyes and swimming in a current. You will be turned by the current and pointed downstream in less that 15 seconds. Thus, the swim path of this injured pod from the beach back to the seaquake epicenter SSW of Hobart can be depicted by tracing upstream from the stranding beach. Satellite data is necessary.
The resistance in the water to swimming in any direction other than downstream prevents the non-navigating whales from heading upstream or even parallel to the flow. The path of least resistance for injured whales is ALWAYS DOWNSTREAM with the flow of the current.
One can easily verify this simple fact by closing your eyes and swimming in a current. You will be turned by the current and pointed downstream in less that 15 seconds. Thus, the swim path of this injured pod from the beach back to the seaquake epicenter SSW of Hobart can be depicted by tracing upstream from the stranding beach. Satellite data is necessary.
IN THE MILLIONS OF YEARS WHALES HAVE BEEN STRANDING, NO POD HAS EVER RESTRANDED UPSTREAM FROM THE ORIGINAL STRANDING SITE.
The injured whales will always restrand downstream!
The reason why whales mostly strand on a beach in the first place is because the current that carried each grain of sand to build the beach is the same energy that directs the whales to the sandy area.
Seaquake injured whales are forced to swim along at 2-4 knots in the direction of the current in order to stay afloat and avoid shark attack. If the current moves at 2 knots and the whales swim at 3 knots, the pod will travel downstream ~5 nautical miles per hour or ~125 nautical miles per day. This means that if a seaquake wounded pod survives for 30 days, they could travel over 3,000 miles for the point of injury. However, the current meanders and often goes around and around in circles (eddies), especially in the Tasman Sea.
This researcher has detailed over 300 strandings and found that the average distance following the flow of the current downstream is ~2,500 miles from the seaquake epicenter to the stranding beach. If the stranding occurs much closer to the epicenter of the seaquake (in distances and in time) the odds are greatly increased that the pod can be successfully refloated since they are in much better health and far less stressed.
The average time between injury and beaching is about 30 days. Packs of sharks follow the wounded pod like wolves dogging a herd of elk. The hungry sharks will snatch an straggler. Many small sharks are prevented from feeding by bigger sharks. These small sharks are ravished and will attack anything in the water.
SWIMMERS MUST AVOID THE WATER WHEN SEAQUAKE INJURED WHALES ARE IN THE AREA.
Below is a chart depicting the average current for the month of January 2011. The earthquake was epicenter SSW of Tasmania where the 50S line intersects the 140E line.
There was also another earthquake in the same area that occurred on January 4, 2011. However, the shallow 5.6 Mw event hypo-centered only 2 km below the seafloor was likely twenty times more dangerous especially since it came only 90 minutes after another seaquake.
Capt. David Williams
Deafwhale Society, Inc.
Capt. David Williams
Deafwhale Society, Inc.
0 comments:
Post a Comment