MASS STRANDING OF PILOT WHALES: FOR KIDS

For information on methods used to detect pilot whales underwater, see www.t-podporpoiseclickdetector.co.uk.

Pilot whales are known to be susceptible to mass strandings, which means that the animals exit the water, generally on beaches, coves, and inlets, somewhere along the coast. At the time of writing this text, the most recent mass stranding occurred on February 17th 2017 in South Island, New Zealand, shortly before the OSC directors Ian and Victoria Todd were visiting the country (see Figure1).

Figure 1: Volunteers care for a pod of stranded pilot whales as they prepare to refloat them after one of the country’s largest recorded mass whale strandings. Photograph: ©Anthony Phelps/Reuters 20017. Source: The Guardian.

Figure 1: Volunteers care for a pod of stranded pilot whales as they prepare to refloat them after one of the country’s largest recorded mass whale strandings. Photograph: ©Anthony Phelps/Reuters 20017. Source: The Guardian.

The precise reason for mass strandings in pilot whales is currently unknown, and could be due to several factors; there are many theories. Since pilot whales are highly social animals, it is thought that when members of the pod, especially the ‘pilot’, becomes ill or is disorientated, the pod will follow them into shallow (and potentially treacherous) waters.

Whales use calls to communicate and identify each other. Strong man-made (anthropogenic) sound has potential to mask pilot whale calls, possibly causing difficulties for individuals to relocate their pods, particularly during deep dives. Military SONAR used in defence activities to find submarines, and side-scan SONAR (Figure 2), used to survey the sea floor also has potential to cause strandings, though scientific evidence at least for pilot whales, is scant.

Figure 2: Side-scan SONAR. A signal is sent from a transducer (in yellow) and it bounces back off hard objects on the seafloor, giving an image on a computer screen (source NOAA. There is currently no hard evidence that side scan-sonar causes stranding in pilot whales, but strandings have occurred when this method has been in use.

Loud anthropogenic noise has the potential to deafen whales’ temporarily and permanently, as well as interfere with their ability to echolocate, causing disorientation. During deep dives this can also trigger individuals to make a rapid accent leading to decompression sickness, which is known in beaked whales. When humans and whales dive, nitrogen from the air in their lungs moves into their body tissues and builds up. The deeper and longer the dive, the more nitrogen builds up. If the diver rises to the surface too fast, the nitrogen is released as bubbles and these bubble damage the divers internally and this illness is known as decompression sickness or the ‘bends’. Again, more scientific evidence is required to ascertain this as a cause of strandings in pilot whales.

Another recent theory for mass strandings in whales involves sun (solar) eruptions disturbing biological internal magnetic senses. Many animals have been discovered to possess the ability to sense magnetic fields surrounding the earth and utilise this ‘internal compass’ for orientation. Fin whales, for example, have been suspected of using this magnetic compass for migration. Eruptions from the sun can cause solar magnetic storms to travel to earth disrupting the magnetic field, which may affect internal magnetic compasses, causing animals to become disorientated. In terms of whales, this could lead to mass strandings. To view another video of a mass stranding in Florida: https://www.youtube.com/watch?v=cbM6_AzD5nI.

 

OSC theory as to why pilot whales may strand

Strandings from pilot whales occur often the shallow, complicated waters of sandy inlets and bays, where sediments are moving continuously, rendering it very difficult for pilot whales to ‘remember’ where they are. Since pilot whales used their SONAR in a similar way to how humans use sight to know where they are, if an animal is unable to get a ‘fix’ on its location because the underwater sand dune that was there yesterday has moved, then they could end up in shallower water. Under special circumstances, tides can move faster than animals can swim, so if the tide goes out, the animals could be left high and dry.

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