Sperm whale (Physeter macrocephalus)
The sperm whale is the largest toothed whale and the most sexually dimorphic whale. Sperm whales are found in all oceans of the world, but they are concentrated in areas of high productive and deep water. Males and females have quite different distributions. Females tend to remain below 40° latitude, whereas large males can be found right up to the southern limits of the ice in the North Atlantic. The most characteristic feature of this whale is its huge, blunt head that makes up the front third of the body.
The sperm whale is the largest toothed whale and the most sexually dimorphic whale. Males can attain a length of 16 metres and a weight of 45 tons while females are considerably smaller, reaching a maximum length of about 12 m and 15 tons. The most characteristic feature of this whale is its huge, blunt head that makes up the front third of the body. The dorsal fin is low and quite rounded. The flippers are paddle-shaped and the fluke has a fairly straight trailing edge with a significant central notch. The dorsal parts of the body are uniformly dark grey, but there are white markings on the lips and lower jaw, and sometimes there are light blotches on the belly. The blow of the sperm whale is low and diffuse for a whale of its size, but it is quite characteristic in that it blows off toward the left side of the animal rather than straight upward. Sperm whales show their flukes when diving deeply; the underside is dark.
Sperm whales are found in all oceans of the world, but they are concentrated in areas of highly productive and deep water. Males and females have quite different distributions. Females tend to remain below 40° latitude, whereas large males can be found right up to the southern limits of the ice in theNorth Atlantic. Only males are found as far north as Svalbard. In mid-latitudes there is a north-south seasonal migration, with them moving pole-ward in summer. Females appear to occupy home ranges whereas males show more variable movement patterns; some remain in coastal waters over periods of years, while others roam much more widely.
There is thought to be approximately 6,200 sperm whales in the Northeast Atlantic region. Females are highly social and live together with other females and their young in groups that usually number about 12 individuals. Groups containing young calves stagger their diving activities such that some adult animals are always on the surface with the calves. Groups can join together with others for some days at a time, and females have been documented to shift groups. Members of a group are very cohesive and perform group defence against predators, forming tight clusters with calves on the inside of the group. Sperm whales are sometimes very active at the surface, breaching, lobtailing and rolling, while at other times they simply rest close together. Young males leave their mother’s pod and form bachelor schools with similarly sized males. As males grow older the groups they occur in shrink in size, until very large males become solitary. Sperm whales perform quiet squeals and trumpets, but for the most part the sounds they produce are high frequency clicks. The most common click trains are thought to be echolocation; used as a means of finding food. However, some stereotyped click trains likely have a social function. Sperm whales are very deep divers, and are largely benthic feeders. Routine dives are to 400 m for periods of 35 minutes, but they can dive to vast depths for periods of over one hour. The maximum recorded depth is 3,000 m. Sperm whales predominantly eat squid but also eat large fish that inhabit deep waters. Killer whales are their principle predator, although it is thought that large sharks may pose a threat to young animals.
Life history and reproduction
Sperm whales have a gestation period of 14-16 months and calves are suckled for several years, although they start eating solid food before they are 12 months old. The specific time of mating and birthing is not known. Large, mature males migrate south for breeding purposes, and are intermittently observed associating with female groups. Females reach sexual maturity when they are about nine years old. They give birth about every five years thereafter. Males reach sexual maturity at about 10 years old, but are unlikely able to participate in mating before they are 20 or more. Longevity is not known, but sperm whales are thought to live to be over 70 years of age.
Management status and monitoring
Hunting of sperm whales commenced in the early 1800s and by the middle of that century thousand of animals were taken annually. This species was highly valued because of the superb quality of the oil from the spermaceti organ. It is thought that whaling, particularly that which occurred following World War II, significantly reduced sperm whale numbers, particularly males because these large animals were preferred. There is no current hunting of sperm whales in theNorth Atlantic region. Sperm whales are protected inSvalbard.
MOSJ indicators (Environmental Monitoring of Svalbard and Jan Mayen):
Awaiting results from MOSJ…