15. Nov, 2017

Body rubbing and pooping: the sperm whales way of socializing

The Sperm whale (Physeter macrocephalus)  is  a highly social and   gentle mammal. Its behavior certainly not justifies the reputation of ferocious monster created by Melville when the describes the deadly struggle between the white whale Moby Dick and the obsessed captain Ahab.

Left: skin pattern of a sperm male after exfoliation of the skin (author unkown)

Sperm whales are the largest predators on earth. They also have the largest brain in the animal kingdom, and can dive over 7000 feet deep to find their favorite food, the giant squids. It  thanks its name to its enormous head,  almost one third  of the size of  its body  (15-18 meters). The large head  of the sperm whale functions as one big sonar system. The sperm whale produces ‘clicks’  (sound burst of short duration) with a pair of phonic lips (also known as "monkey lips" or "museau de singe") at the front end of the nose, just below the blowhole. Sperm whales often swim in small social units or pods, although several pods  may form larger groups or clans distributed over  a much larger area. Recent studies have shown that  families and clans  have their own  'dialect':  typical signatures of sound bursts called codas.  Using these codas sperm whales recognize vocalizing individuals  of other social units that share a similar dialect.

Although sperm whales  usually swim in small groups  there are periods  when they gather in much greater numbers at certain locations.  These periodical meetings have the character of ritual meetings or ‘get togethers’ were several clans meet members of other clans. Resembling the pow wows, the social gatherings held in the past by different Native American communities.  

An area  where these gatherings can be observed by snorkelers is  Dominica in the  Western Carribean.  The ocean floor along Dominica's west coast drops steeply to several thousand feet very close to shore, providing a calm and sheltered area for a large group of resident sperm whales to feed, mate, and socialize. Year round, they can be spotted very close to shore, cruising up and down the island's coast. On occasions as many as 70 animals come together for hours or days at Dominica. Here  some remarkable forms of behavior have been  observed and photographed  by  UW photographers  Keri Wilk from Canada and Tony Wu from the USA, which also has shed more light on the function of these gatherings.  It appears that the major incentive for these cetaceans  to  gather periodically  is highly practical,  namely to groom each other by rubbing their massive bodies and  itching skins together. The result of skin rubbing shows up in large chunks of skin floating  on the surface giving the impression of large plastic bags.  As a result the whales start to show white and black camouflage-like skin patterns, where  patches of new skin show up against the old scraped of skin (see picture above).

According to Luke Rendell, a marine biologist at the University of St Andrews, UK. this shedding of skin is part of a natural antifouling mechanism to stop them being encrusted with other marine animals and parasites.  “They love touching against each other and one of the rewards may be exfoliation,” says Rendell.  Even more remarkable  than the  skin rubbing rituals   (called  ‘scratchatons’ by Tony Wu) are the  concurrent  defecations when the whales disperse  clouds of liquid poop looking like chocolate  milk in the water. The whales often show prolonged bowl movements,  unlike the normal defecations when shark return to deeper water. One can only guess about  the meaning  of these Poonados  (a term used by Keri Wilk). Pooping can occur as a a defensive reaction or a sign of anxiety, as sometimes observed in smaller whale species  when feeling insecure. The clouds  produced during defecation could also be a form of camouflage, like the ink-clouds emitted by the octopus.  Another possibility is that adult bulls in the pod use these clouds to  impress rivals or females from other clans. Finally,  whales could simply enjoy the experience, with the reaction to empty their bowels triggered by with the pleasant sensation of skin rubbing. Whatever  the reason, group defecation seems to be  an integral part of large social gatherings for these animals...a group poop, so to speak.  Another question that remains to be answered is  if these mass gatherings perhaps also serve to swap between members of the pods, for example when females or young bulls hop over  to other pods  where their presence is more urgently needed to guarantee  new offspring.


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