Sperm Whale - Sea Watch Foundation

THE SPERM WHALE IN UK WATERS
DESCRIPTION The sperm whale Physeter
macrocephalus is the largest whale of the
odontocete (toothed whales) family; males grow
to over 18 m and females to 12.3 m in length.
Sperm whales are highly sexually dimorphic with a
physically mature male being almost one and a
half times as long as a physically mature female.
The most distinctive feature of the sperm whale
is the huge, square head, which is one third, to
one quarter of the total body length. Its lower
jaw is underslung and extremely long and narrow
and it has no fin but distinct triangular or dorsal
hump two-thirds along the body, followed by the spinal ridge. Corrugations on the skin give a shrivelled
appearance and it is dark brown or grey in colour. The lips and lower jaw are white. There may be white
patches in the genital region and sometimes elsewhere on the body. The belly and front of the head may
be whitish to grey and carves are lighter in colour than adults. The sperm whale can be identified at sea by
its bushy blow (1.5-5.0m high) directed forwards and to the left. It may
lie like a log on the surface with its broad, triangular and deeply
notched tail flukes thrown into the air.
DISTRIBUTION The sperm whale has an extensive distribution worldwide.
There are no population estimates as yet for the North Atlantic
population. Nevertheless, it may be found throughout all deep oceans
of the world, from the equator to the edge of the polar pack ice, with
major breeding areas including the Caribbean and around the Azores.
The species also occurs in the Mediterranean Sea.
In Northern Europe, the greatest number of sperm whale records come
from the British Isles, probably reflecting their Atlantic position close to
the edge of the continental shelf, (sperm whales rarely come onto the
continental shelf), as well as the long history of organised strandings
and sightings recording schemes there.
SOCIAL BIOLOGY Sperm whales can remain submerged for over 2 hours, but typical dive time is less than 45
minutes. They frequently breach and lobtail. Sperm whales form a variety of different school types that
may vary with season and location. In high latitudes, usually only lone adult males or bachelor schools are
seen. Adult females and their female offspring form family units known as matrilines. Female sperm whales
are among the most sociable of all mammals. They often form groups of about twenty animals that cooperate in defending themselves, babysitting
and even suckling each other’s young. The males
however only stay with their family unit until
about six years old, spending the rest of their
lives alone or with other males. Adult males
join these family groups only intermittently and
mainly during the breeding season.
Some
schools may be segregated according to age or
reproductive status, but these can coalesce to
form larger loose, unsegregated groups.
Breeding groups can range in size from four to
150 or more animals.
REPRODUCTIVE BIOLOGY Sperm whales are
seasonal breeders but with a prolonged mating
season, and calving occurring anytime between
May and September. The gestation period is
thought to be 14.5 to 16.5 months. In the
Northern Hemisphere, conceptions may occur
from January to August, peaking in April and May
and in the Southern Hemisphere, from July to
March, peaking in September and December.
Sperm whale calves observed off Sri Lanka were
found to associate closely with several other
school members in addition to their mothers.
They were often found at the surface with such
adults who may have been performing a ‘baby
sitting’ role. The calving interval is generally 3 to
6 years.
DIET The sperm whale feeds primarily upon large squid, older
males tending to take larger prey than do females and
younger males. It is virtually the only species feeding upon
very large cephalopods, which places it as one of the major
components of the top trophic level of the pelagic ecosystem.
Other cephalopods such as benthic octopuses, and medium to
large-sized demersal fishes such as rays, sharks, and many
teleosts, are also taken. In high latitudes, the diet of large
males may comprise 67-98% fish. Males eat more fish than
females, including rays, shark and teleosts. Crustaceans are
rarely eaten, although large benthic crabs and the giant
mesopelagic mysid Gnathophausia have been found in the
stomachs of a number of sperm whales.
THREATS Between 1950 and 1987, more than 20,000 sperm whales were killed by whale fisheries, mainly
around Iceland, the Azores, Madeira and Spain. This came to an end in the late 1970’s early 1980’s.
However over more recent years, an increase in mass sperm whale strandings in northern Europe has been
noted. There are several possible reasons for this. It could reflect a population increase, as a result of the
cessation of hunting, or a change in migration behaviour with more animals moving into high latitudes, and
food shortages in the winter increasing mortality. Accidental capture in fishing gear, mortality due to toxic
contaminants such as PCB’s, or physical
damage from intense sounds, seismic, military
or oceanographic detonations, could also all
have a part to play. In the Mediterranean
sperm whales are among the cetacean species
known to die as bycatches, entangled in Italian
drift nets. The number of annual mortalities is
unknown but thought to be around 30 a year.
FURTHER READING
Cooke, J.G. 1985. Trends in abundance of sperm whales in the western North Pacific. Rep. Int. Whal. Commn 35: 205-208.
Evans, P.G.H. 1987. The Natural History of Whales and Dolphins. Christopher Helm, London. 360pp.
Evans, P.G.H. 1992. Status Review of Cetaceans in British and Irish waters. Sea Watch Foundation, Oxford.
Evans, P.G.H. 1995. Guide to the identification of whales, dolphins and porpoises in European Seas. Sea Watch Foundation, Oxford.
Evans, P.G.H. 1997. Ecology of Sperm Whales (Physeter macrocephalus) in the Eastern North Atlantic, with special reference to
sightings and strandings records from the British Isles. Pp. 37-46. In Sperm Whale Deaths in the North Sea Science and Management.
Editors Thierry G. Jacques and Richard H. Lambertsen. Bull. de L’Institut Royal des Sciences Naturelles de Belgique. Biologie. Vol. 67
- Supplement. 133pp.
Evans, P.G.H. 1995. Guide to the identification of whales, dolphins and porpoises in European seas. Sea Watch Foundation, Oxford.
IWC 1981. Report of the subcommittee on sperm whales. Rep. Int. Whal. Commn, 31: 78-102.
Reid, J., Evans, P.G.H. and Northridge, S.P. 2003. Cetacean Distribution Atlas. Joint Nature Conservation Committee, Peterborough.
68pp.
Rice, D.W. 1989. Sperm whale Physeta macrocephalus Linnaeus, 1758. In. S.H. Ridgway and R.J. Harrison (Eds), Handbook of Marine
Mammals. Vol. 4. River dolphins and larger toothed whales. Academic Press, London. 430pp. Pp. 177-233.
Smeenk, C.S. 1997. Strandings of sperm whales Physeter macrocephalus in the North Sea: history and patterns. Pp. 15-28. In Sperm
Whale Deaths in the North Sea Science and Management. Editors Thierry G. Jacques and Richard H. Lambertsen. Bull. de L’Institut
Royal des Sciences Naturelles de Belgique. Biologie. Vol. 67 - Supplement. 133pp.