A study of the heads of sperm whales has confirmed a 19th-century whaler's theory, and given credibility to stories of sperm whales destroying ships several times their weight.
During the peak of the whaling era, the capacity to fight back was a very useful attribute for sperm whales (Physeter macrocephalus). Modern metal whaling ships might be beyond the capacity of even the mightiest giant of the sea, but wooden whaling boats were vulnerable to enraged whales. Herman Melville's "Moby-Dick" is perhaps the most famous of the stories of whales turning themselves into battering rams to destroy their tormentors. The novel was inspired by true events, portrayed in the recent film "In The Heart Of The Sea".
This posed a puzzle, however. Where had sperm whales gained this capacity? Selective whaling pressure had not given them time to evolve such a talent.
“After a large male rammed and sank his ship in the Pacific in 1820, whaler Owen Chase described the whale’s head as admirably designed for this mode of attack,” said Dr. Olga Panagiotopoulou of the University of Queensland in a statement. “The scientific community received the ramming hypothesis with reluctance. This was mainly because the front part of the sperm whale head houses sensitive anatomical structures that are essential for sonar communication between whales, and they would be in harm’s way in a ramming event.”
Moreover, Panagiotopoulou, pointed out, eyewitness accounts of ramming are rare.
In PeerJ, Panagiotopoulou modeled the effect of a sperm whale ramming an object of similar, or larger, size. “The immense forehead of sperm whales is possibly the largest, and one of the strangest, anatomical structures in the animal kingdom,” the paper noted. “It contains two large oil-filled compartments, known as the 'spermaceti organ' and 'junk,' that constitute up to one-quarter of body mass and extend one-third of the total length of the whale.”
No other whale has a head shaped like the sperm whale, (center left). Yyang/Shutterstock
Although this was already known, Panagiotopoulou found that connective tissue in the junk reduces impact stress on the skull, making it possible for sperm whales to ram objects without breaking their upper jaws or damaging other sensitive organs. Such ramming would come at a price; Panagiotopoulou refers to reports of scarring in the junk of dead sperm whales. This is consistent with her findings that the whale would suffer more damage if it took a hit near the spermaceti organ than near the junk.
Our knowledge of sperm whale behavior is limited. Nevertheless, Panagiotopoulou told IFLScience a wildlife pilot reported seeing two mature males headbutting each other near a group of around 50 females. She added that other cetaceans, including orcas and narwhals, have been seen to engage in ramming contests.
Unusually for cetaceans, male sperm whales are around three times the size of the female, a characteristic common in species where males fight for mates. Consequently, it seems likely that male sperm whales evolved their remarkable heads to better fight off rivals, and then put them to good use when threatened by wooden whaling ships.
The curious content of male sperm whales' heads made them attractive prey for whalers, but also gave them a chance to fight back. Ali Nabavizadeh/PeerJ