Sperm whale

Physeter macrocephalus, the sperm whale, is a toothed whale with a huge head: males reach about 16 m and some 45 tons, females about 12 m and some 15 tons ^[1]. It hunts squid and fish on deep dives lasting up to 45 minutes ^[1]. Last century it was the large cetacean most heavily hunted in Peruvian waters, where 49,858 were killed between 1951 and 1981 ^[2]. On the 1995 to 2002 cruises it was seen mostly far offshore, in the north and south of the country, and its global IUCN Red List category is Vulnerable ^[2],[3].

Linnaeus described the species in 1758 as Physeter macrocephalus, and that same year gave it three further names, Physeter catodon, Physeter microps and Physeter tursio, now all treated as synonyms ^[4]. Clarke and colleagues preferred Physeter catodon and used it throughout their series on Southeast Pacific sperm whales, although the accepted name is Physeter macrocephalus ^[5],[4]. The English name "sperm whale" refers to spermaceti, the waxy substance held in its head ^[1].

It is the only living cetacean whose single blowhole is offset to the left side of the head ^[1]. The head takes up roughly a third of the body length; the lower jaw is narrow and carries 20 to 26 large teeth per side, while the upper teeth hardly ever break through the gum ^[1]. It is dark grey, sometimes with white patches on the belly, and the skin behind the head is often wrinkled; the flippers are small and paddle-like, the dorsal fin low, thick and usually rounded, and the flukes triangular ^[1].

Males and females differ greatly in size: females measure about 12 m and weigh some 15 tons, while males reach about 16 m and 45 tons ^[1]. In the Southeast Pacific female calves are born at about 3.90 m ^[5]. A probably immature female stranded on Llostay beach, Tacna, in July 2015 measured 8.20 m and had 21 pairs of functional teeth ^[6].

Similar species

• Kogia breviceps: The pygmy sperm whale is far smaller, under 4 m, with a pointed, shark-like snout, a narrow lower jaw set back under the head, and a mark behind the eye resembling a gill opening ^[7]. Peruvian regulations group it with the small cetaceans and the sperm whale with the large ones ^[8].
• Kogia sima: The dwarf sperm whale looks so much like the pygmy sperm whale that the two are very hard to tell apart at sea ^[7]. Peruvian regulations list it, like the pygmy sperm whale, among the small cetaceans, and the sperm whale among the large ones ^[8].

It lives in all deep oceans, from the equator to the edge of the Arctic and Antarctic ice. In some populations adult males make long migrations into temperate waters, while females and calves stay in tropical waters all year ^[1].

IMARPE's 21 research cruises between 1995 and 2002 logged 38 sperm whale sightings between 3° and 18° S; all but 2 were in oceanic waters beyond the continental shelf ^[2]. They clustered in the north, from 7° S to the Ecuadorian border, and in the south, from 16° S to the Chilean border; sea surface temperature at the sightings ranged from 16.02 to 29.1 °C ^[2].

Whales in the north probably belong to the Ecuador and northern Peru stock, while those in the south are likely linked to whales off northern Chile ^[2]. The rise in sightings in 2001 and 2002 was larger than natural growth could explain, and was read as animals arriving from the offshore Southeast Pacific, from Galápagos or from further away ^[2]. The management plan of the Mar Tropical de Grau National Reserve describes the Máncora Bank as habitat above all for deep-diving cetaceans, sperm whales among them ^[9].

It hunts on deep dives that often reach about 600 m and last up to 45 minutes, resting at the surface for several minutes between dives ^[1]. It eats squid, sharks, skates and deep-water fish, taking 3 to 3.5% of its body weight each day ^[1].

Females form units of about 12 females with their young. Young males leave between 4 and 21 years of age and join others of similar age, and the largest males usually travel alone ^[1]. Females use codas, patterns of clicks, in social settings; recordings made in the South Pacific and the Caribbean between 1985 and 2000 sorted the social units into 6 vocal clans, 5 of them Pacific and 1 Caribbean, whose overlapping ranges cover thousands of kilometres ^[10].

Reproduction in the Southeast Pacific was worked out from 1105 females examined between 1959 and 1962 at the whaling plants of Paita and Pisco, in Peru, and Iquique and Talcahuano, in Chile: here females reach sexual maturity at about 8.2 m and 6.5 years, earlier than in other seas ^[5]. Gestation lasts about 17 months, nursing about 19 and the whole cycle about 4 years; mating peaks in September and births in February ^[5]. Females stop growing at 11.2 m and about 33.5 years, and can live for at least 50 years ^[5].

On the Peruvian cruises of 1995 to 2002 groups held between 1 and 18 animals, 3.5 on average; a lone whale was the commonest sighting, and groups of 3 or more made up 39.5% of sightings ^[2]. Of the 15 groups of 3 or more animals, 14 were in water of 16 to 21 °C ^[2].

Its relative abundance off Peru tended to rise when the sea was warmer than normal, although El Niño years blurred that link ^[2]. During the 1982-83 El Niño, whalers found sperm whale concentrations 600 km further south than usual ^[2].

Its diet in the region is debated. Squid beaks from the stomachs of sperm whales taken off Peru and Chile suggested that the jumbo squid, Dosidicus gigas, made up 32% of what they ate, but it did not turn up in faeces collected at Galápagos, and in both cases the main prey were squids of the genus Histioteuthis ^[2]. Even so, between 1995 and 2002 sperm whale abundance indices closely tracked the catch per unit effort of the jumbo squid fishery, which hints at some trophic link ^[2].

Its global IUCN Red List category is Vulnerable ^[3]. It is on CITES Appendix I ^[1] and, since 2002, on Appendices I and II of the Convention on Migratory Species, which also runs a concerted action for sperm whales of the eastern tropical Pacific ^[11].

An estimate published in 2002 put the world population at about 360,000 sperm whales; by the same study, in 1999 some 32% of the pre-whaling population remained, which would have numbered around 1,110,000 ^[12].

Heavy whaling in Peruvian waters probably had effects beyond Peru: between 1985 and 1995 the females and immatures that visit Galápagos declined by about 20% a year, mainly because they moved towards the mainland coast, and the near disappearance of large breeding males from the region lowered pregnancy rates ^[13].

Between 1995 and 2012, 15 cases of large cetaceans entangled in fishing gear were confirmed in Peru, 3 of them sperm whales, and gillnets accounted for 80% of them ^[14]. In September 2015 an immature 12.4 m male stranded on Pozo de Lizas beach, Moquegua, entangled in fishing gear with a buoy, and died about 4 hours later ^[6].

Ministerial Resolution No. 451-2019-PRODUCE lists the sperm whale among the large cetaceans, which must not be approached closer than 100 m, or 300 m when they are feeding or socialising; it also bans heading towards groups with calves and requires any collision or entangled animal to be reported to IMARPE and the maritime authority ^[8].

From 1800 into the 1980s it was one of the main targets of commercial whaling, which nearly wiped out its populations; its spermaceti went into oil lamps, lubricants and candles, and the International Whaling Commission set a moratorium on commercial whaling in 1986 ^[1].

It was the most exploited large cetacean in Peruvian waters: between 1951 and 1981 Peruvian whalers killed 49,858 sperm whales, and whaling stopped in 1982 ^[2]. As early as 1961, data from the Pisco station already pointed to probable overexploitation ^[2].

Between 1959 and 1962 Peru had whaling stations at Paita, Pisco and, now and then, Chancay; at Paita and Pisco 656 and 355 females were examined, most of the material from which the species' reproduction in the Southeast Pacific was described ^[5].

Off Peru it is found mostly in oceanic waters beyond the continental shelf; on the 1995 to 2002 cruises it was seen more in the north and south of the country than in the centre ^[2]. The 2026 management plan of the Mar Tropical de Grau National Reserve names the Máncora Bank as one of its habitats, but also notes that it was not detected during cetacean sightings off northern Peru, although it is probably present ^[9],[9].

In the south, the 2025 management plan of the San Fernando National Reserve includes it among the 13 cetacean species recorded between the mouth of the Ica River and San Fernando ^[15]. Between 2001 and 2015 at least 6 strandings were documented on the coasts of Arequipa, Moquegua and Tacna ^[6]. Anyone who meets one at sea must stay at least 100 m away ^[8].