School
of black-fish stranded on the shore of Cape Cod, Massachusetts, 1902.
Black Fish or Pilot Whales are small toothed whales intermediate
in size between dolphins and the larger whales. They frequently
form schools particularly while migrating and sometimes will end
up stranded like this after swimming into the wrong bay or
estuary, the tide goes out, they still try to swim in the wrong
direction and they get stranded.
Laying on their sides, they cannot support their
weight in air and have the problem that internal organs are
crushed under their own weight. In particular they face breathing
difficulties in expanding their lungs with muscles that are
unpractised
at doing so with the mass of their body on top of the lungs. The
skin also dries out and may crack. Tragically such strandings
result in the death of the whales, in more recent times,
volunteers have kept whales moist and tried to keep them alive and
refloat them when the tide returns, though sometimes the whale
then attempts to swim back in the direction that led to it being
stranded in the first place.
Such strandings are now thought to be the result
of temporary changes in the earth's magnetic field. Cetaceans
migrate by following low density magnetic lines and disturbances
of the earth's magnetic field that varies regularly within set
limits cause the whales to take the "wrong turning" with
disastrous results. Such fluctuations happen more commonly at coasts,
probably exacerbated by the fact that rocks that may be magnetic
are more likely to be shallower and so nearer to the whales.
Such a use of magnetism for navigation is found
more commonly in animals that live in the water than terrestrial
animals except for birds, which of course use this sense when some
considerable distance away from the earth (and again possibly
magnetic rocks).
Image courtesy NOAA
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