Although originally described by Linnaeus in 1758 as four different species of the Genus Physeter, today the sperm whale is recognized as the only species in a monotypic family separate from the two species of the family Kogiidae (the dwarf and pygmy sperm whale).
The sperm whale has a controversial but ultimately descriptive latin name as well as an unfortunately abbreviated common name.For years a debate raged over which of the two names given to the sperm whale by Linnaeus, P. macrocephalus or P. catodon, was most approriate. Recently, however, the former has been given priority and is generally accepted. Physeter macrocephalus describes the species well as it literally tranlates to "blower with a big head". Its common name has been abbreviated from the original "spermaceti whale". The name is derived from the milky-white substance found in the sound producing organs in the animals head named spermaceti oil by whalers due to its resemblance to semen.
Size, shape and distinctive characteristics
Easily distinguished at sea from all other cetaceans by their unique block-shaped heads which can make up to one third of its length in males. A large hump around the s-shaped blowhole is found at the front, left side of the head which produces a distinct a low, bushy blow which is angled to the left side of the whale's body; allowing for identification even from a distance in fair weather. A tube-shaped, dark-colored, wrinkled body leads back, past small, paddle-shaped flippers, to a small, lumped dorsal fin. Several, irregularly spaced, ridges stretch the length of the peduncle, or tailstalk. When diving they lift their relatively large, triangular flukes.
The sperm whale is truly an animal of extremes. The sperm whale is the largest toothed whale. Among cetaceans, the sperm whale displays the largest difference in body size between the sexes as males can reach up to 18 meters or 60 feet and weigh up to 60 metric tonnes or 125 000 lbs, while the females are about a third shorter and half as heavy. The sperm whale also has the largest brain and the longest intestine on the planet. Calves are born at about 4m or 13ft and the average weight at birth is around 1 metric tonne or about 2200 lbs.
They have a uniquely slender, underslung lower jaw with large cone-shaped teeth which fit into sockets in the toothless upper jaw. The block-shaped head is the result the selection for the most powerful natural sonar system and the development of a large nasal complex containing the oil-filled spermaceti and "junk" organs which are unique to the members of the super-family Physeteroidea.
A truly cosmopolitan distribution, sperm whales may be found from the Arctic to Antarctica in waters greater than 1000m or 3000ft depth including most coastal seas. Adult females and immature animals of both sexes remain in tropical and subtropical waters, while mature males disperse towards the poles in either direction. Larger males disperse farther than younger, smaller males such that a gradient in the size of the males exists as you move from the equator to the poles.
Ecology and Behaviour
It should be noted that virtually all our current knowledge on sperm whale social behaviour is based on longitudinal studies in the Pacific Ocean, however, more recent work in the Atlantic and its coastal gulfs and seas is uncovering interesting similarities and contrasts.
Social Structure: Constant Companions and Casual Acquaintances
The social structure of the female and immature sperm whales is hierarchically organized into several levels based on differing spatial and temporal scales.
Female and immature sperm whales, reside in sub-tropical and tropical waters and live in stable social groupings, called "Units". Members of the same social unit are associated over decades and are thought to be constant companions. Unit members are often, but not always, matrilineally related. Units range in size from the smaller units of the Caribbean (~7 animals) to larger units in the Pacific (~12 animals). Associations within a unit appear to be correlated with relatedness.
In the Pacific, individual social units associate for periods of a few days with other units to form what are called "Groups". These are casual acquaintances over a few hours to days in which two or more units are associated. In contrast to work in the Atlantic, the group tends to be the assemblage that is most commonly observed at sea in the Pacific.
Finally, tens of thousands of sperm whales make up one of several "Vocal Clans" each with a distinct vocal dialect. Members of different vocal clans also appear to differ in their movement patterns, habitat-use, feeding success, diet, and reproductive success.
The social structure in the Meditterranean appears to be much less defined with animals often been sighted alone.
The most prevalent vocalization pattern of sperm whales is the ‘usual' click, which is produced by foraging whales as echolocation at depth. Socializing whales sometimes produce short stereotyped sequences of clicks, termed ‘codas', which have also been recorded at the beginning of foraging dives and just prior to surfacing. Sperm whale social units have different repertoires or dialects as they show different usage patterns of specific codas. In the Pacific, units preferentially associate with units possessing similar coda dialects, such that these dialects appear to represent a higher-order social structure, termed the vocal clan. Because clans in the Pacific are sympatric and are genetically similar to other clans, it has been argued that differences in repertoires between clans most likely result from social learning.
A sperm whales life is roughly analogous to other K-selected mammals. Sperm whale gestation is approximately 15-18 months. Sperm whales nurse for 2-4 years during which time they do not appear to dive deeply with thier mothers. As a result, other members of the calf's natal unit remain at the surface to babysit while its mother is at depth feeding. Calves appear to begin fluking at around 3 years of age. Sexual maturity for both sexes is in their early teens, although males slightly later than females. Only young males disperse from their natal unit and do so between 6-12 years of age, but it is thought that there is significant individual variation. Although they are known to form loose batchelor groups, males live primarily solitary lives in colder waters until "social maturity" around 30 years of age at which point they return to warmer waters to rove singly between units looking for mates. Calving rate is around one every four years. Although evidence for menopause for females in their fourties is inconclusive, it is likely that older females rarely give birth as individuals can reach as old as 70.
The sperm whale is among the longest (possibly up to 2 hrs) and deepest (~2000m or ~1.2 miles) divers among all cetaceans. Sperm whales dive this deep in order to feed primarily on mesopelagic squid which range in size from the smallest at 100g or 0.2 lbs to the famous Giant Squid which weighs around 100kg or 220 lbs. In a single year, the global population of sperm whales remove about 75 megatons or 165 billion pounds of squid and fish from the ocean. This number is comparable to the total annual catch of all human marine fisheries in recent years. Sperm whales are clearly a significant element in the pelagic ecosystem, particularly given recent insight into top-down ecological effects in marine food webs.
Targets of the Yankee whalers from the east coast of the US during the 18th and 19th centuries, sperm whales were killed primarily for their spermaceti oil. Modern hunts, from 1945 to 1984, also focused on sperm whales, particularly in the Pacific. Although the sperm whales are considered protected by the IWC a few sperm whales are taken under the auspices of a "scientific" whaling program in Japan. Prior to the hunts, sperm whales numbered in the millions, but the most recent estimate puts the global population of sperm whales at around 360 000 animals.
The status and stock structure of sperm whales has not been considered by the IWC in many years and large areas are considreed to be single stocks. The entire North Atlantic, for example, is considered one stock partially due to the capture of males tagged and killed on opposite sides of the ocean. However, recent photographic and molocular studies have suggested high degrees of female philopatry and genetic differentiation even given the wide male dispersal. As a result, it is the ranging patterns and habitat-use of the female social units that is most relevant for management and conservation.
The sperm whales are listed under Appendix 1 and 2 of the Bonn Convention on Migratory Species, Appendix 3 of the Bern Convention, Appendix 1 of CITES, and Appendix 4 of the EU Habitats Directive. This species is protected under the US Endangered Species Convention and the Marine Mammal Protection Act, but as of 1996 are listed as "Not at Risk" by COSEWIC in Canada and are not listed under the Canadian Species at Risk Act. Sperm whales are Protected by the IWC and are currently listed a Vulnerable in the IUCN Red List of Threatened Species 3.1. It has been argued that the distinct sub-population in the Meditterranean should be listed separately as Endangered.
With a few exceptions, the primary threat to sperm whales, directed hunts, has all but ceased. However, lingering effects of these massive removals may still remain. The selective removal of large males may have depressed pregnancy rates, particualrly in the Pacific. While the removal of females may have resulted in the loss of socio-ecological knowledge as has been shown by the removal of older females in elephants, a terrestrial mammal with very similar social-structure and ecological success.
Outside of whaling, however, this speceis is still impacted by a number of threats. Interactions with fisheries have recently been in the spotlight with mature males depredating long-line gear in several locations around the world. In that Meditterranean, however, the main concern surrounds gillnet entangelments. Recent global surveys have shown that pollutants; such as PCBs, DDT, and heavy metals, can be found at high levels everywhere including more remote regions like the Antarctic. Sperm whales are also the focus of various whale watching operations worldwide, the impacts of which are still unclear. Lastly, but perhaps of most concern, ocean noise from sonar, global shipping, and seismic exploration for oil is increasingly garnering attention as a major conservation issue for many cetacean species.
Because of the widespread and generally offshore distribution of this species it is likely that impacts of various factors are underreported and with a maximum rate of increase estimated around 1% per year, any recovery is expected to be slow.
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