A group of sperm whales.
Photo: Chris Johnson
June 12, 2001
Sperm Whale Socialization
Sperm whales are cosmopolitan animals. They inhabit the blue waters of all of the world's oceans and are well known as the most social of all the great whales. Mature females together with juveniles and calves of both sexes, form social groups. These social groups are restricted to tropical and sub-tropical waters. Males disperse from their natal family at around six years of age, moving to the higher latitudes where they will age and grow. When they mature sexually at around twenty-five years of age, the bulls leave their bachelor schools and usually becoming solitary.
Some males tend to migrate seasonally to the equator in their late twenties in the pursuit of females. Sperm whales also exhibit the greatest sexual dimorphism of any cetacean, with females averaging 11 meters in length, while mature males can literally be double the size of the females (although size differences vary between oceans depending upon exploitation, when larger males in particular were targeted). This differentiation in size and habitats, is also reflected in behavioral differences between the social groups in the tropics and the old males in Polar Regions.
Members of a social group usually dedicate most of their time to deep and long dives in the quest for food. The feeding dives are apparently synchronized, as the adult females and juveniles fluke up within the same 10-min. interval, stay submerged for approximately 40 minutes and return to the surface in a coordinated manner. We have observed this behavior several times when in the company of sperm whales. For a period of ten minutes we observe whales blowing around the Odyssey in all directions, then we are left alone at the surface until the group completes its dive with only their chorus of clicks on the acoustic array to keep us company.
When tracking sperm whales we often find them to be spread out over large areas, sometimes tens of square miles foraging individually, or in association with one or two other animals. A likely explanation for this behavior is to avoid any interference or competition for prey items.
Small calves cannot follow the adults on such deep and long dives, they are either left alone on the surface, looked after by their mother or other members of the group. Calves can be vulnerable to predation from large sharks or orcas. Sometimes we have observed lone calves at the surface, travelling at a considerable pace. On more than one occasion an adult has surfaced not more than twenty meters from it. It has been suggested that calves actually follow the clicks of the group from the surface so as not to get lost or be left behind.
It seems that perhaps once a day, or every few days, a dispersed group will come together and rest, travel slowly or socialize at the surface. We have observed large groups apparently resting in close proximity to one another on several occasions in Papua New Guinea. At times, such groups have consisted of five or six animals and others close to twenty-five or thirty. During these times, the whales seem very relaxed and more tolerant of our approaches, which allows the Odyssey crew to observe their behavior and collect valuable data.
Almost everything about the lives of sperm whales remain a mystery to scientists. However, if we continue to observe them in a benign manner in their natural habitat, we will learn a lot more about the habits of this living mammal than from the supposed scientific whaling efforts currently being practiced by some countries.
This is Genevieve Johnson speaking to you on another warm tropical day from Madang in Papua New Guinea.
Log by Genevieve Johnson