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Sperm Whale
Behaviour
Breeding Behaviour
Females reach sexual maturity as young as 7 and as old as 13
years of age (Wilson and Ruff 1999). They enter estrus every 3
to 5 years and calve once every 3 to 6 years. Gestation takes
14 or 15 months and the calves nurse for at least another two
years. Males reach puberty at 7 to 11 years and become
sexually mature when they are 18 to 21 years old (Wilson and
Ruff 1999). Male sperm whales are 11.0 to 18.3 meters long
and weigh 11,000 to 57,000 kilograms. Female’s are8.3 to 12.5
meters long and weigh between 6,800 and 24,000 kilograms
(Wilson and Ruff 1999).
Social Organization
Whitehead’s (2003) book on the social organization of the
sperm whale eloquently describes the social behaviour and
ecology of the sperm whale. A sperm whale is born into a
“vigorous social milieu” of its mother (Whitehead 2003). The
calf weighs about a ton at birth and it is most often a
singleton. Young sperm whales appear to stay close to their
mothers’ nomadic groups that travel about 35,000 kilometers
over a year (Whitehead 2003). As the young whales reach
teenage years, the females stay with their mothers and
conceive their first calves at about 9 years of age. Calves
are raised by the communal group. She will give birth every 4
to 6 years early in her life until she is in her forties when
she will bear a calf every 15 years. Females will live well
into old age perhaps reaching a century (Whitehead 2003).
Females and calves tend to stay in the warmer waters at low
latitude. It is likely these older females aid the young
females in raising calves. Young males, on the other hand,
depart their mothers’ care between 3 and 15 years of age to
form bachelor groups. These groups tend to move farther north
as they age until the largest males now in their forties,
become loners near the ice edge of the far north.
Breeders usually consist of 20-40 females of mixed ages
including immature males and females but can be as large as
150 animals. Associated with each of these breeding groups are
1-5 socially dominant mature males. Breeding lasts from
January to August reaching a peak activity between March and
June. Bachelor groups have up to 50 young males and sexually
mature females. In addition to these two groups are solitary
males (Wilson and Ruff 1999).
Sperm whales have long been known to have strong social bonds
between members (whithead 2003). They form into rosettes when
attacked by
killer whales in which they put their heads together with
the tails pointing out like spokes in a wheel. Individuals
separated from the group under attack are rescued by other
members who leave the rosette to escort them back to relative
safety (Pitman and Chivers 1999). Whalers also remarked how
the group came to the rescue of wounded individuals (Beale
1839 reported by Whitehead 2003).
Whitehead (2003) contends that sperm whales possess the
essential elements of a culture. These are specific features
that allow groups to be distinguished as clans. He suggests
that there are 4 or 5 clans in the South Pacific based on
distinctive calls of the clans, habitats used by clans and
associations of individuals in the clans. The scientific
community is not without its detractors over Whitehead’s
hypothesis which he summarizes in his 2003 book.
Feeding Behaviour
Sperm whales feed nearly exclusively on squid and octopi with
only the occasional shark, skate and ray being taken (Wilson
and Ruff 1999). They suck prey into their mouths and swallow
them whole despite the presence of large teeth. They catch
their prey at great depths often diving for 1.5 hours. An
early remarkable diving record was of a sperm whale entangled
in an underwater cable at 1135 meters but more recent records
reach to 2250 meters. These are unusually long and deep dives;
most dives are less than half an hour and less than 500 meters
deep.
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