The Sperm Whale is the largest of the toothed whales, or Odontocetes (1), and is one of the common cetacean species in the Mediterranean Sea (2).
P. macrocephalus has a very distinctive body shape, dominated by the spermaceti organ in the head (3) resulting in the characteristic large, rectangular shaped head (4). The head makes up almost one third of the body length (1). The blow hole is located near the tip of the nose (5) and its blow is distinguishing as it is angled forward (1). The sperm whale has a small, underslung jaw (3) with 20-30 large conical teeth (4) which fit into holes in the upper jaw (6). The dorsal fin is reduced to a hump, and smaller bumps run down the length of the anterior dorsal ridge (5). The pectoral fins are small and blunt (5). Males can reach up to lengths of 25m (4), although 18m length is more common (5; 3). Females are smaller than males (4; 5) averaging at 11m (7). The body is, most often, a uniform dark grey-brown colour (4; 5).
Sperm whales occur in two groups; nursery groups and bachelor groups (8). Nursery groups contain adult females, and calves and juveniles of both sexes (8). Bachelor groups are loosely associated and consist of mature males, however males are more often solitary (9). Sperm whales are unusual, and maybe even unique, in the level of alloparental care given to young (10). This means that within the nursery group calves and juveniles are looked after by 10-30 different adult females (10). This unusual social structure means that the young are always under the care of an adult, for example, juveniles sometimes cannot join the mother while foraging as the depth is too great, so the juvenile is accompanied at the surface by other adults to protect them from predators (11).
The diving behaviour of the Sperm Whale has been extensively studied in different areas of the world (2). Typically sperm whales dive for 40-50 minutes and then spend roughly 8 minutes on the surface recovering (2). The dive can be split into three phases: (1) the descent phase, preceeded by the fluke up which indicates the whale is descending vertically; (2) the foraging phase, where foraging depth is reached and the whale hunts horizontally; and (3) the ascent phase, where the whale returns to the surface (12). Sperm whales detect their prey using clicks and creaks (13).
Sperm whales display a highly marked sexual dimorphism in length with males reaching a length almost 1.6 times the length of females (14; 7). Females reach sexual maturity at age 9 when they are roughly 8m in length, whereas males attain sexual maturity at 19 when they are around 13m long (14). Mating season can be as long as 7 months, from January to August, with calving occurring from May and September (15). The gestation period is thought to be as long as 15-16 months (14). Calves are born at 4m length and the mother lactates for 2 years, upon weaning the juvenile has almost doubled in length (14). The female will not become pregnant again until the calf is 3 to 6 years old (15).
It is inferred, from the presence of calves in the Mediterranean that female sperm whales remain in the Mediterranean to breed (16).
Sperm whales are mainly found in continental slope areas and deep water (17), specifically in waters deeper than 1,000m that are not covered by ice (18).
The Sperm whale has a large geographic distribution and is seen in all of the world’s oceans except the Poles however it mainly inhabits continental slope areas and deeper waters (17).
It has recently been discovered that Sperm whales in the Mediterranean are not visitors as previously thought, (4) but a resident population that, due to restricted movements through the Straits of Gibraltar, are becoming genetically distinct from Atlantic populations (16). It has also been demonstrated that there is a feeding segregation in the Mediterranean sperm whale population. It has been shown that large males tend to feed in the north, whereas larger nursery groups containing juveniles feed in the south during summer months (7).
The majority of odontocetes (toothed whales) capture single prey, as opposed to mysticetes (baleen whales) which are ‘batch feeders’ (19). This also means that odontocetes feed throughout the year, and are therefore tied to areas where prey is abundant all year round (19).
P. macrocephalus uses echolocation to locate prey in a complex but accurate set of clicks and creaks (13). In the Mediterranean it has been found that the individual Sperm Whale studied fed almost exclusively on squid (20). Sperm whales also feed on benthic invertebrates, small and large squid, small- and mesopelagics and miscellaneous fish (21).
Listed as Vulnerable under the IUCN Redlist (17).
CITES Appendix I (Listed under the synonym Physeter catodon) (22).
Bern Convention Annex II (23).
CMS Appendices I and II (24).
Description written by Sarah Marjoram (2009)
(1) Society, A.C., 1999-2009. American Cetacean Society Fact Sheet: Sperm Whale, Physeter macrocephalus. [Online] Available at: http://www.acsonline.org/factpack/spermwhl.htm [Accessed 15 July 2009].
(2) Drouot, V..A.G.a.J.C.G., 2004. Diving and feeding behaviour of Sperm Whales (Physeter macrocephalus) in the north-western Mediterranean Sea. Aquatic Mammals, 30(3), pp.419-26.
(3) Reynolds III, J.E..D.K.O.a.S.A.R., 1999. Marine Mammals of the World. In J.E.a.S.E.R. Reynolds, ed. Biology of Marine Mammals. Washington and London: Smithsonian Institution Press.
(4) Riedl, R., 1986. Fauna y flora del mar Mediterraneo. Barcelona: Ediciones Omega, S.A.
(5) Geraci, J.R.a.V.J.L., 1993. Marine Mammals Ashore: A field guide for strandings. Texas, U.S.A.: Texas A&M Sea Grant College Program.
(6) Kinze, C.C., Unknown. Marine Mammals. [Online] FAO Available at: ftp://ftp.fao.org/docrep/fao/009/y0870e/y0870e67.pdf [Accessed 16 July 2009].
(7) Drouot, V..A.G.a.J.C.G., 2004. Summer social distribution of sperm whales (Physeter marcocephalus) in the Mediterranean Sea. Journal of the Marine Biological Association United Kindom, 84, pp.675-80.
(8) Anon., n.d. Physeter catodon, Sperm Whale. [Online] Available at: http://marinebio.org/species.asp?id=190 [Accessed 16 July 2009].
(9) Gannier, A..V.D.a.J.C.G., 2002. Distribution and relative abundance of sperm whales in the Mediterranean Sea. Marine Ecology Progress Series, 243, pp.281-93.
(10) Whitehead, H., 1996. Babysitting, dive synchrony and indications of alloparentat care in sperm whales. Behavioural Ecology and Sociobiology, 38, pp.237-44.
(11) Papastavrou, V..S.C.S.a.H.W., 1989. Diving behaviour of the sperm whale, Physeter macrocephalus, off the Galapagos Islands. Canadian Journal of Zoology, 67(4), pp.836-46.
(12) Gordon, J.C., 1987. The behaviour and ecology of sperm whales off Sri Lanka. PhD Thesis. Darwin College, University of Cambridge.
(13) Miller, P.J.O..M.P.J.a.P.L.T., 2004. Sperm whale behaviour indicates the use of echolocation click buzzes ‘creaks’ in prey capture. Proceedings of the Royal Society London B: Biological Sciences, 271, pp.2239-47.
(14) Boyd, I.L..C.L.a.H.D.M., 1999. Reproduction in Marine Mammals. In Reynolds III, J.E.a.S.A.R. Biology of Marine Mammals. Washington and London: Smithsonian Institution Press.
(15) Foundation, S., n.d. The sperm whale in UK waters. [Online] Available at: http://www.seawatchfoundation.org.uk/docs/Sperm_Whale.pdf [Accessed 16 July 2009].
(16) Drouot, V. et al., 2004. A note on genetic isolation of Mediterranean sperm whales (Physeter macrocephalus) suggested by mitochondrial DNA. Journal of Cetacean Resource Management, 6(1), pp.29-32.
(17) Taylor, B.L..R.B.J.B.S.M.D.J.F.J.G.M.G.N.d.S.P.W.&.R.L.P., 2009. Physeter macrocephalus. [Online] IUCN Available at: www.iucnredlist.org [Accessed 14 July 2009].
(18) Whitehead, H., 2003. Sperm Whales: Social evolution in the ocean. Chicago: University of Chicago Press.
(19) Wells, R.S..D.J.B.a.G.B.R., 1999. Behaviour. In Reynolds III, J.E.a.S.A.R. Biology of Marine Mammals. Washington and London: Smithsonian Institution Press.
(20) Roberts, S.M., 2003. Examination of the stomach contents from a Mediterranean sperm whale found south of Crete, Greece. Journal of the Marine Biological Association of United Kingdon, 83, pp.667-70.
(21) Pauly, A..A.W.T.E.C.a.V.C., 1998. Diet composition and trophic levels of marine mammals. ICES Journal of Marine Science, 55, pp.467-81.
(22) UNEP-WCMC, 2009. UNEP-WCMC Species Database: CITES-Listed Species. [Online] Available at: http://www.unep-wcmc.org/isdb/CITES/Taxonomy/tax-species-result.cfm/isdb/CITES/Taxonomy/tax-species-result.cfm?source=animals&displaylanguage=eng&genus=Physeter&species=catodon&tabname=legal [Accessed 15 July 2009].
(23) Europe, C.o., 2002. Convention on the conservation of European wildlife and natural habitats: Bern Convention. [Online] Available at: http://conventions.coe.int/Treaty/FR/Treaties/Html/104-2.htm [Accessed 15 July 2009].
(24) (CMS), C.o.t.C.o.M.S.o.W.A., Effective 5th March 2009. Appendices I and II of the Convention on the Conservation of Migratory Species of Wild Animals.