OIL and its multiple functions
A
large sperm whale can have as much as ten thousand gallons of oil stored in a
large organ above the upper jaw and in front of the skull. The oil was dipped out by whalers of the past
several hundred years until whaling was stopped due a great reduction in sperm
whale numbers. Even more oil was stored
in the blubber in a thick inner layer of the skin. The oil was a valuable commodity leading to a major maritime industry in the United States during its developmental years.
ECHOLOCATION, FEEDING, AND COMMUNICATION
Smaller
toothed relatives such as dolphins and porpoises have a similar, but much
smaller, organ called a melon in a similar position on their heads. They are thought to function in echolocation
by focusing sound waves sent out to produce echoes that enable the sender to
identify the objects in their environment.
Some sounds sent out may be used to stun or disorient prey as well. Baleen whales are better known for their many
sounds, but both must be able to use sound for communicating with others of
their species over vast distances. The sperm whale is said to produce the loudest sound of any animal. It is thought to have a small structure, at the rear of the anterior air chamber where the connecting duct to the posterior chamber is located, that is where the sound originates.
ENERGY STORAGE, INSULATION, AND BUOYANCY
The
blubber of all the large whales is important for storing energy for long trips
away from their feeding areas. In the
sperm whale it serves as insulation when diving into deep waters where
temperatures stay only a few degrees above freezing. Oil in blubber also helps balance the weight
of bones to give closer to neutral buoyancy.
The buoyancy provided by air in the lungs and passageways would be
greatly reduced by pressure. It would
have about one-half the volume at thirty feet of depth, one-quarter at ninety
feet, one-eighth at 210 feet, and less than 1% of the original volume on the
deepest dives.
ORIENTATION SENSING
The
large oil store in the head of the sperm whale has some connective tissue and
two air chambers with a connecting duct that could possibly serve as a
mechanism for providing information of orientation in the water more reliably
than the minute inner ear mechanism of most other animals. If residual air in
the lungs were transferred to the air sacs during deep dives it would provide
less vascular surface area for nitrogen to enter the blood. What really happens is unknown. But it would seem that the uppermost chamber
would have the most air and signal the direction of the surface; a survival
mechanism that would be useful to a whale groggy from too long at great depth. When the chambers are in a vertical position
relative to each other, they could shift the center of gravity appropriately to
help keep the orientation maintained on course when either diving or returning
to the surface as well as aiding the sensory cues involved.
Nitrogen
is much more soluble in sperm oil than it is in blood. So it could help protect from nitrogen
bubbles forming when return to the surface occurs from great depths. The small quantity of air taken down with
them may also help. But exchange is not
likely to have enough blood circulated close to the oil as the circulatory
system shuts down less essential areas during a dive to make this function of
much importance.
The
large head oil storage organ bulges like an enormous nose that could also
provide some shock absorber protection if they bumped into a rock bottom or
submerged objects. Evolution can lead to multiple functions developing for the same feature. So energy storage, flotation, echolocation, communication, adjustment of center of gravity, and insulation, and mechanical protection can all be compatible uses for the oil stored in a sperm whale's head.
Sperm
whales have a few large conical teeth on the lower jaw that fit in toothless
sockets on the upper jaw when the mouth is closed. The teeth may attract squid by mimicking a
school of fish in dim bioluminescence of the deep sea when the lower jaw is
open.
The Great Sperm
Whale, a book by Richard
Ellis (2011, University Press of Kansas), is a interesting account of the sperm
whale’s natural history and the story of the whaling industry from the
perspective of an author with a love of whales and service on the International
Whaling Commission to the time a moratorium was placed on sperm whale
hunting. Hal Whitehead is one of the
more prolific sources of information on sperm whales in recent decades.
Joseph
G. Engemann September 16, 2013
