Buoyancy as a Function of the Spermaceti Organ

Photo taken by Leslie Smith off Abaco Island, Bahamas of two whales logging on the surface. It was assumed that the pair are a mother and calf.

Buoyancy Hypothesis

The buoyancy hypothesis involves the incorporation of a possible thermoregulation function of the spermaceti organ with physical poperties of the spermaceti oil (Lockyer 1997, Clarke 1978a, Morris 1975, Morris 1973). With this hypothesis, a heat exchange function of the organ results in density changes of the oil that helps to regulate the sperm whales buoyancy during a dive (Clarke 1978a). Simply by dropping the spermaceti oil temperature by 3C, a whale could become neutrally buoyant during a dive of 200m (Clarke 1978a). The temperature would then drop a specific amount to balance the lift for each depth the sperm whale achieves (Clarke 1978c). It then should be able to control its buoyancy by alternately heating and cooling the lipids in the spermaceti organ (Cranford 1999). There three physical properties of spermaceti oil, that make this possible: the relationship between its density, temperature, and pressure; heat exchange during freeze and melting; elevation of its temp during increases in pressure (Clarke 1978c). Hypothetically, sea water is drawn into the right naris to cool down the spermacti oil (Cranton 1999).

  This buoyancy control is possible due to the distribution of blubber over the body of the sperm whale. This distribution may provide stability in buoyancy due to density changes of blubber with temperature during a dive.

 

This hypothesis contend that buoyancy is maintained due to two factors:

- Skin blood vessels dilate when the dive is commenced (Clarke 1978a)

- vasodilation and bradycardia are terminated while the animal is still at depth (Clarke 1978a)

Photo taken by Leslie Smith off Abaco Island, Bahamas of the same two whales seen in the picture above with one of them blowing.

 

Problems with the Buoyancy Hypothesis

Buoyancy seems an unlikely function of the spermaceti organ for many proximal and evolutionary reasons. Firstly, none of the structures that you would associate to being present within a heat exchanging organ such as a capillary rete complex, exclusive vascularization, or counter current exchange sys, or increased surface area in thermal units over which heat can be exchanged (Cranford 1999). Additionally, the two factors outlined above with the dilation of vessels are not plausible mechanisms for sperm whales because they would counteract any oxygen convsering mechanisms that allow the sperm whales to go on prolonged dives (Cranford 1999). Thermal regulation by drawing in sea water to the right naris is implausible as it would cause difficulties with osmoregulation in the nasal mucosa and surrounding nasal tissues (Cranford 1999). This influx of sea water could also bring with it foreign microorganisms that could lead to infection (Cranford 1999).

The creation of such a large store of fat like the spermaceti organ requires a large investment from the individual. The question then becomes, even if the mechanisms were in place in which thermoregulation of the spermaceti oil was possible, would it be worth it calorically. How could a floating mechanism repay such a huge investment? Any buoyancy control from the spermaceti organ would be negated any, most likely, because the compression of pulmonary gases during the dive would ofset any buoyancy gained from congealing liquid spermaceti (Cranford 1999).

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