Aggression as a Function of the Spermaceti Organ

Photo Courtesy of Greenpeace, Rex Weyler. This photo depicts a Sperm Whale that has been harpooned by a whaling boat.

 

Moby Dick: Fact or Fiction

During the 19th century, sperm whales were aggressively hunted for their high quality oil found in their spermaceti organ (Carrier et al 2002). The oil that was harvested was used to fuel lanterns. Sperm whales were also convenient to hunt because they floated after they were slaughtered, making htem easier to tow behind the whaling boats (Clarke 1978a). Sperm whales, however, were difficult to hunt, and feared, because they are extremely aggressive, leading to such tales as Moby Dick by Herman Melville (Carrier et al 2002). Sperm whale hunting still occurs today but is illegal because sperm whales are considered a protected species.

Herman Melville's book, Moby Dick, in 1851 gave a fictional account of a whaling vessel, the Pequod, that was destroyed by the very sperm whale they were hunting. Though this book is a work of fiction, real occurences of these attacks did happen. There are numerous stories of large, male, sperm whales sinking whaling ships by ramming the ships with their heads (Carrier et al 2002).

 

The first documented case of a sperm whale ramming, and consequently sinking, a ship was in 1821 involving the Essex (Carrier et al 2002). In this case, the 238 ton ship built of white oak was sunk by a 26 meter long male sperm whale that repeatedly rammed the ship with its head (Carrier et al 2002).

Another instance of this aggression was seen in 1851 with the sinking of the Ann Alexander (Carrier et al 2002). In this case, after being harpooned by row boats, the sperm whale attacked two of the the row boats crushing them in its jaws (Carrier et al 2002). The crew on the remaining row boats then got back on the main boat and further pursued the whale until it turned on them again and smased a whale head size hole in the boat causing it to sink (Carrier et al 2002).

 

 

Photo Courtesy of National Oceanographic and Atmospheric Administration Corps, Scott Hill. This photo depicts the back of a Sperm Whale on the surface with a view of its blowhole on the left side of its head.

Head butting behavior

Head butting behavior in sperm whales generally occurs during male-male aggression in contests for female mates (Carrier et al 2002). During these head butting competitions it is the spermaceti organ that is used as a battering ram (Carrier et al 2002). Therefore spermaceti organ size could be a sexually selected trait, the larger the organ, the more ramming power, the higher the fitness. Similar head-butting behavior has been seen in bottle nosed whales that do not contain spermaceti organs for the purpose of mate selection (Carrier et al 2002).

 

 

Evolutionary Support

The evolution of relative melon (weapon) size in cetaceans (including sperm whales) is positively correlated with the evolution of sexual dimorphism in body size which is also correlated with the degree of polygyny (Carrier et al 2002). Sperm whales are sexually dimorphic not only in overall body size, but, the spermaceti organ itself is relattively larger in males than females (Carrier et al 2002). In terms of evolved effectiveness, the spermaceti organ of a charging sperm whale has enough momentum to seriously injured an opponent (Carrier et al 2002).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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