Feeding, behaviour and diving: Sperm Whales, along with Bottlenose whales, are the deepest-diving mammals in the world. They are believed to be able to dive up to 3000 metres in depth and 2 hours in duration to the ocean floor. More typical dives are around 400 metres in depth and 30-45 minutes' duration. They feed on several species, in particular giant squid, octopuses and demersal rays. Almost all we know about deep sea squid has been learned from specimens found in captured Sperm Whale stomachs. Stories about titanic battles between Sperm Whales and Giant Squid which may be 10 metres long or more are perhaps the stuff of legend — such a battle has never been observed. However, white scars on the bodies of Sperm Whales are believed to be caused by squid. It is also hypothesized that the sharp beak of a consumed squid lodged in the whale's intestine leads to the production of ambergris, analogous to the production of pearls. Sperm Whales are prodigious feeders and eat around 3% of their body weight per day. The total consumption of prey by Sperm Whales worldwide is estimated to be about 100 million tons — a figure comparable with the total consumption of marine animals by humans each year.
The physiology of the Sperm Whale has several adaptations to cope with drastic changes in pressure when diving. The ribcage is flexible to allow lung collapse, and the heart rate can decrease to preserve oxygen supplies. Myoglobin stores oxygen in muscle tissue. Blood can be directed towards the brain and other essential organs only when oxygen levels deplete. The spermaceti organ may also play a role (see above).
Between dives the Sperm Whale will come up to the surface for breath and remain more or less still for eight to ten minutes before diving again.
The social structure of the Sperm Whales species divides on sexual lines. Females are extremely social animals, a trait believed to derive from their relatively simple evolutionary path. Females stay in groups of about a dozen individuals and their young. Males leave these 'nursery schools' at somewhere between 4 and 21 years of age and join a 'bachelor school' with other males of a similar age and size. As males grow older they tend to disperse into smaller groups and the oldest males typically live solitary lives. Yet mature males have been stranded on beaches together, suggesting a degree of co-operation not yet fully understood.
The Sperm Whale is among the most cosmopolitan species in the world. The species is relatively abundant from arctic waters to the equator. Populations are more dense close to continental shelves and canyons, probably because of easier feeding. Sperm Whales are usually found in deep off-shore waters but may be seen closer to shore in areas where the continental shelf is small.
Population and hunting:
The total number of Sperm Whales throughout the world is unknown. Crude estimates, obtained by surveying small areas and extrapolating the result to all the world's oceans, range from 200,000 to 2,000,000 individuals. Although the Sperm Whale was hunted for several centuries for its meat, oil (used as a lubricant in submarines) and spermaceti (used in candles) the conservational outlook for Sperm Whales is brighter than that for many other whales. Although a small scale coastal fishery still occurs in Indonesia, they are protected practically worldwide. Fishermen do not catch the deep-sea creatures that Sperm Whales eat and the deep sea is likely to be more resistant to pollution than surface layers. However, the recovery from the whaling years is a slow process, particularly in the South Pacific, where the toll on males of a breeding age was severe.
Watching Sperm Whales:
Sperm Whales are not the easiest of whales to watch due to their long dive times and ability to travel long distances underwater. However, due to the distinctive look and large size of the Sperm, watching is increasingly popular. Sperm Whale watchers often use hydrophones to listen to the clicks of the whales and locate them before they surface. Popular locations for Sperm Whale watching include the picturesque Kaikoura on New Zealand's South Island, where the continental shelf is so narrow that whales can be observed from the shore, and Andenes in arctic Norway.
In the news:
In July 2003 a huge blob of white flesh was found washed up on a beach on the coast of southern Chile. The 40-foot-long mass of gelatinous tissue gave rise to speculation that a previously unknown giant octopus had been discovered. However researchers at the Museum of Natural History, Santiago concluded that the mass was in fact the innards of a Sperm Whale, a conclusion drawn by looking at the dermal glands. When a Sperm Whale dies its internal organs rot until the animal becomes little more than a semi-liquid mass trapped inside the skin. In this case the skin eventually burst causing the internal mass to float free and eventually wash up on the beach .
January 2004 saw a more dramatic entry of the Sperm Whale into the global media spotlight. A dead specimen of the whale, 17 metres long and weighing 50 tons, had washed up on a local beach in Tainan City, Taiwan. On being transported to a university in the city, gas pressure from decomposition built up inside the body, causing an explosion. Nobody was hurt, but blood and entrails were spread over several cars and surrounding pedestrians . Main article: exploding whales
Dead Sperm Whales float towards shore quite often. Apart from the disposal issues identified above, beach managers fear that sharks, in particular the Great White Shark, will be attracted towards the beach by the rotting flesh, and potentially cause danger to beach-users. For this reason dead Sperm Whales are often towed out to sea before they become properly beached. This occurred twice in May 2004, once off Oahu in Hawaii where a dead whale was towed out 35 miles to sea but floated back to shore two days later.
References: Whales & Dolphins: The Ultimate Guide to Marine Mammals, Carwardine, Hoyt, Fordyce and Gill, Collins Books.
National Audubon Society Guide to Marine Mammals of the World, Alfred A. Knopf Publications.
Encyclopedia of Marine Mammals, Perrin, Wursig and Thewissen.
Cetacean Societies Field Studies of Dolphins and Whales, Mann, Connor, Tyack and Whitehead.
On The Trail Of The Whale (chapter 1), Carwardine.