Monday, September 16, 2013
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.
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