dolphins
data card 3
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dolphins
data card 3
Facts
about dolphins
PART
3: Why do dolphins and whales get stranded on beaches?
Mass
strandings: Why?
If a single whale or dolphin strands, it usually
is a very sick (and exhausted) animal.
Such an animal often has some infections
(pneumonia is almost always one of them) and
a lot of parasites (worms
in the nasal passages are very common). Sometimes these animals
can be rehabilitated, but often they are so sick they won't make it.
Some
species of whales and dolphins occassionally strand in groups. A
stranding of 2 or more animals is usually called a mass stranding.
There are a number of theories that try to explain the occurrence of
mass strandings. No theory can adequately explain all of them. In some
cases it will be a combination of causes. The most common explanations
are:
-
deep water animals (the species that most often are the victim of mass strandings) can not "see" a sloping sandy beach properly with its sonar. They detect the beach only when they are almost stranded already and they will panic and run aground. [1]
-
whales and dolphins may be navigating by the earth's magnetic field. When the magnetic field is disturbed (this occurs at certain locations) the animals get lost and may run into a beach. [2]
-
in some highly social species, the group leader may be sick and wash ashore. The other members try to stay close and may strand with the group leader.[3]
-
when under severe stress or in panic, the animals may fall back to the behavior of their early ancestors and run to shore to find safety. [4]
Adapted from Dolphin FAQ maintained by Jaap van der Toorn (jaap@compuserve.com)
sources:
[1]
W.H. Dudok van Heel (1962): Sound and Cetacea. Neth. J. Sea Res. 1:
407-507
[2]
source: M. Klinowska (1985): Cetacean live stranding sites relate to
geomagnetic topography. Aquatic Mammals 11(1): 27-32
[3]
F.D.
Robson (?) The way of the whale: why they strand. (unpublished manuscript)
[4]
F.G. Wood (1979) The cetacean stranding phenomena: a hypothesis. In:
J.B. Geraci and D.J. St. Aubin: Biology of marine mammals: Insights
through strandings. Marine Mammal Commission report no: MMC-77/13: pp.
129-188
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