Sperm whale

 

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Classification:

Global Population

Description and Natural History

Physical Description
Sperm whales are the largest of the toothed whales and exhibit the highest degree of sexual dimorphism (difference in size or physical characteristics between males and females) of any cetacean. Males are substantially larger than females, averaging 15 meters (49 feet) in length; females average 10 meters (33 feet). Calves are born 3.5 - 4.5 meters (11 - 15 feet) long and weigh about one tonne (1.1 tons).

Sperm whales have a large blunt head which makes up almost 1/3 the entire length of the body. The square head is noticeably larger on males than on females and projects noticeably beyond the long, narrow, toothed lower jaw. Adults are slate gray or brown to black while calves are lighter gray overall. Adults have white on the belly and at the front of the head, as well as around the mouth. Sperm whales have a wrinkled appearance beginning behind the head that is readily apparent in photographs.

The rounded or triangular hump situated where the dorsal fin would be, and the "knuckles" down the tail stock, are clearly visible when the animal arches before a dive. A "keel" on the belly may also be apparent as the animal throws up its tail flukes prior to a dive. The flukes are large and triangular with a straight trailing edge, except for a deep central notch. Because the blowhole is located on the front, left side of the head, the bushy blow is forward and angled.

Natural History
Sperm whales are distributed globally from the Arctic to the Antarctic and are most abundant in offshore deep waters, although they may venture close to shore if underwater canyons or other deep waters are available. Females and the young live in stable social units that are partially matrilineal. Adult males move into high latitudes while females and young are usually found in tropical to warm-temperate waters.

Females reach sexual maturity between eight and 11 years of age and males at about ten years, although they probably do not mate until age 18 or 20. Calves are born every three to six years after about a 14 to 15-month gestation. Calves are weaned at about 18 months although sporadic suckling may continue.

Sperm whales are long, deep divers reaching depths of 1,000 meters (3,280 feet) while foraging for their preferred prey, deep-water squid. Dives of 2,800 meters (9,186 feet) and two hours duration have been recorded. They may be acrobatic at the surface, lobtailing or breaching. Sperm whales emit broadband click-type vocalizations for the majority of the time they are underwater. These are thought to be a form of echolocation. Sperm whales also produce repeated patterns of clicks -- sometimes referred to as ‘codas’ -- which are thought to have some social significance.

There is no global abundance estimate for sperm whales.

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Status of the Species

Status
Sperm whales are listed as Vulnerable by the International Union for the Conservation of Nature and Natural Resources (IUCN) and are included on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

They are also listed under various state and national protective legislation, including the US Endangered Species Act (ESA) under which they are listed as Endangered.

Threats to the Species

Sperm whales have been commercially hunted since the 1700s. Most population stocks have been substantially reduced by whaling. Factory ship whaling for sperm whales was prohibited by the International Whaling Commission (IWC) in 1979. Despite the moratorium on whaling, Japan recently began hunting sperm whales in the North Pacific for "scientific" purposes. In 2000, Japan landed five sperm whales. The meat and other products, such as oil, from these "scientific" whaling operations are then sold in Japan on the open market. Other threats to sperm whales include collisions with large vessels; net entanglements; ingestion of marine debris; oil spills and dumping of industrial wastes; and noise pollution from seismic operations, sonar and other sources. International Trade Listed on CITES Appendix I which prohibits international trade.

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Authors and Sources

CITES. 2001. Physeter macrocephalus. http://www.cites.org.

Christal, J. and H. Whitehead. 2001. Social affiliations within sperm whale (Physeter macrocephalus) groups. Ethology 107 (4), 323-340.

Environment Australia Online. 2001. Sperm whale.

www.environment.gov.au.

IUCN. 2001. The 2000 IUCN Red List of Threatened Species. http://www.redlist.org.

Jefferson, T.A., S. Leatherwood and M.A. Webber. 1993. Marine mammals of the world. FAO Species Identification Guide. UNEP, Rome. 320pp.

Leatherwood, S. and R.R. Reeves. 1983. The Sierra Club Handbook of Whales and Dolphins. Sierra Club Books, San Francisco. 302pp.

Rice, D.W. 1998. Marine mammals of the world: Systematics and distribution. Special Publication Number 4. The Society for Marine Mammalogy. 231pp.

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