Physeter macrocephalus

Physeter macrocephalus

The sperm whale (Physeter macrocephalus, Linnaeus, 1758) is a cetacean belonging to the Physeteridae family.

Systematic –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Phylum Chordata,
Subphylum Vertebrata,
Superclass Tetrapoda,
Mammalia class,
Subclass Theria,
Infraclass Eutheria,
Superorder Laurasiatheria,
Order Artiodactyla,
Infraorder Cetacea,
Physeteridae family,
Genus Physeter,
Species P. macrocephalus.
The terms are synonymous:
– Catodon australis MacLeay, 1851;
– Catodon australis Wall, 1851;
– Catodon colneti Gray, 1850;
– Catodon (Meganeuron) krefftii Gray, 1865;
– Catodon macrocephalus Lacépède, 1804;
– Catodon trumpo Lacépède, 1804;
– Cetus cylindricus Billberg, 1828;
– Delphinus bayeri Risso, 1826;
– Meganeuron krefftii Gray, 1866;
– Megistosaurus ensiformis Godman, 1827;
– Phiseter cylindricus Bonnaterre, 1789;
– Phiseter mular Bonnaterre, 1789;
– Phiseter trumpo Bonnaterre, 1789;
– Physalus cylindricus Lacépède, 1804;
– Physeter andersonii Borowski, 1780;
– Physeter australasianus Desmoulins, 1822;
– Physeter australasiensis Desmoulins, 1822;
– Physeter australis Gray, 1846;
– Physeter catodon Linnaeus, 1758;
– Physeter maximus G.Cuvier, 1798;
– Physeter microps Linnaeus, 1758;
– Physeter microps subsp. rectidentatus Kerr, 1792;
– Physeter mular Lacépède, 1804;
– Physeter novaeangliae Borowski, 1780;
– Physeter orthodon Lacépède, 1804;
– Physeter tursio Linnaeus, 1758;
– Physeterus sulcatus Lacépède, 1818;
– Tursio vulgaris Fleming, 1822.
The following subspecies are recognized within this species:
– Physeter australis subsp. asiaticus Gray, 1866;
– Physeter australis subsp. australis;
– Physeter catodon subsp. australis Tomilin, 1957;
– Physeter catodon subsp. catodon;
– Physeter macrocephalus subsp. cinereus Kerr, 1792;
– Physeter macrocephalus subsp. macrocephalus;
– Physeter macrocephalus subsp. niger Kerr, 1792.

Geographic Distribution and Habitat –
The sperm whale is a cosmopolitan species, whose genetic analysis indicates that the world’s population originated in the Pacific Ocean from a population of around 10,000 animals around 100,000 years ago, when the expansion of the polar ice caps blocked their access to other seas. Notably, colonization of the Atlantic was found to occur several times during this expansion of their range.
This cetacean has a wide worldwide distribution and is relatively abundant from the poles to the equator, found in all oceans.
They are found in the Mediterranean Sea, but not the Black Sea, while their presence in the Red Sea is uncertain. Shallow entrances to both the Black and Red Seas could explain their absence.
Coastal areas with significant sperm whale populations include the Azores and Dominica. In East Asian waters, specimens are also regularly observed in coastal waters in places such as the Commander and Kuril Islands, the Shiretoko Peninsula which is one of the few places where sperm whales can be observed from the coast, off Kinkasan, in proximity to Tokyo Bay.
The habitat of the densest populations is close to continental shelves and canyons. Sperm whales are usually found in deep water offshore, but can be seen closer to shore, in areas where the continental shelf is small and drops rapidly to depths of 310 to 920 meters.
They also prefer ice-free waters deeper than 1,000 meters. Although both sexes range across temperate and tropical oceans and seas, only adult males populate the higher latitudes. In several regions, such as along the coastal waters of South Australia, sperm whales are considered locally extinct.
Adult males are also known to enter surprisingly shallow bays to rest (females are in a state of rest during these occasions). There are unique coastal groups reported from various areas of the globe, such as near the coastal waters of Scotland, and at the Shiretoko Peninsula, off Kaikōura, in the Davao Gulf.
The total number of sperm whales worldwide is unknown. Rough estimates, obtained from the reconnaissance of small areas and extrapolating the result from all the world’s oceans, vary from 200,000 to 2,000,000 individuals. Although the sperm whale has been hunted for some centuries for meat, oil and spermaceti, the sperm whale’s conservationist outlook is brighter than that of many other whales. Although a small-scale coastal fishery still survives in Indonesia, it is protected virtually throughout the world. Fishermen do not catch the deep-sea creatures that sperm whales feed on, and the deep sea is probably more resistant to pollution than the surface layers.

Description –
Physeter macrocephalus is the largest toothed cetacean in existence.
The sperm whale is characterized by a very large head, especially in males, which normally occupies a third of the animal’s length. In fact, the most characteristic aspect of the sperm whale comes from its enormous head, which often reaches a third of the animal’s length.
Perhaps unsurprisingly, the sperm whale has the largest and heaviest brain of all known modern and extinct animals (weighing an average of 7kg in an adult male). Despite this, the brain is not large, compared to body size.
The spiracle is located very close to the anterior end of the head, displaced to the left of the midline.
Adult males can reach 20.5 meters in length and weigh up to 57,000 kilograms.
However, there is evidence of larger specimens in the past. The specimen from the Nantucket Island Whale Museum (Massachusetts, United States) has a 5.5 meter long jaw. In the museum we read that this individual was 24 meters long; while the sperm whale that sank the whaling ship Essex (one of the incidents that inspired Moby-Dick) is estimated to have been 26 meters long. Intensive hunting may have reduced the average size of sperm whales, as larger males were the most sought after and captured, especially after World War II. Nowadays, males do not frequently exceed 18.3 meters in length and 51,000 kilograms in weight.
This cetacean presents the most evident sexual dimorphism. At birth, both sexes are nearly the same size, but upon reaching maturity, males are between 30 and 50 percent longer, triple the weight of females, and reach their maximum size at around 50.5 years of age. .
The sperm whale’s hind fins are triangular and very thick, and protrude out of the water when they begin to dive. They have no dorsal fin, but have a series of crests in the caudal third; the longer crest was called a “hump” by whalers and may be confused with the dorsal fin due to its shape.
The tail is triangular and very thin. Before submerging, the animal raises it to a considerable height on the surface of the water.
The flukes (tail lobes) of the sperm whale are triangular and very thick. Proportionately, they are larger than any other cetacean and are very flexible. The sperm whale lifts its fins out of the water as it begins a dive to feed. It has a series of ridges on the caudal third of its back instead of a dorsal fin. The larger crest was called a “hump” by whalers and can be confused with a dorsal fin due to its shape and size.
In contrast to the smooth appearance of the skin of most large cetaceans, the skin of the back has a rough appearance similar to the appearance of the skin of a plum. The skin is normally gray in color; however, under sunlight it acquires a brown color. As with other large cetaceans, there are numerous sightings of albino specimens.
The lower jaw is long and narrow. The teeth fit into notches along the upper jaw.
The sperm whale has between 20 and 26 teeth in each of the two rows of the lower jaw. These teeth have a conical shape and can weigh up to one kilogram each. The purpose of the teeth is unknown, as they do not appear to be necessary for catching or eating squid, as there are records of well-fed, toothless animals. One possibility is that the teeth are used as a means of aggression among males as they often have numerous scars caused by the teeth. The upper jaw also has teeth, but they are rudimentary and rarely emerge into the oral cavity.

Biology –
Sperm whales can live 70 years or more, and their reproductive strategy is associated with stable environmental conditions and includes a low birth rate, significant parental support for offspring, slow maturation, and high longevity.
Males become sexually mature at 18 years old. Once they reach sexual maturity, males move to higher latitudes, where the water is colder and feeding is more productive. Females remain at lower latitudes. Males reach their full size around age 50.
How they choose mates has not been definitively determined. Males fight each other for females, and males will mate with multiple females, making them polygynous, but they do not dominate the group like in a harem. Breeders do not provide paternal care to their offspring, but rather play a paternal role towards younger males to show their dominance.
Females become fertile around 9 years of age. The oldest pregnant specimen ever recorded was 41 years old. Gestation takes 14 to 16 months, producing a single newborn. Sexually mature females give birth once every 4-20 years (pregnancy rates were highest during the whaling era).
Birth is a social event, as the mother and cub need others to protect them from predators. Other adults may push and bite the newborn in his first few hours.
Breastfeeding lasts from 19 to 42 months, but babies can rarely breastfeed for up to 13 years. Like that of other whales, sperm whale milk has a higher fat content than that of land mammals: around 36%, compared to 4% in cow’s milk. This gives it a cottage cheese-like consistency, which prevents it from dissolving in the water before the calf can drink it. It has an energy content of approximately 3,840 kcal/kg, compared to only 640 kcal/kg in cow’s milk.
Pups may be allowed to nurse from females other than their mothers.

Ecological Role –
Physeter macrocephalus is the largest of all Odontocetes and the largest living animal with teeth.
It is one of many species first described by Linnaeus in 1758 in the 18th century work Systema Naturae; he recognized four species in the genus Physeter. Experts later saw that it was only a single species. In the most modern publications, the sperm whale is classified as the only species of the Physeteridae family (that is, it is a monospecific genus). The sperm whale family is sometimes considered a superfamily, Physeteroidea.
Sperm whales were hunted until recently in the Portuguese Atlantic archipelago of the Azores. The sperm whale is also the state animal of Connecticut.
The term “sperm whale” derives from “oil head” and originates from the oily-waxy substance present in their skull.
The social structure of sperm whales is divided according to sex. Females are extremely social animals, a characteristic that is believed to derive from their relatively simple evolutionary path. Females reside in groups of about a dozen individuals with their young. Males leave these “nursery schools” between the ages of 4 and 21 and form “bachelor groups” with other males of similar age and size. As males become older, they tend to disperse into smaller groups, and older males generally lead solitary lives. Some newly mature males have stranded together, suggesting a level of cooperation that is not fully understood.
When it comes to finding food, sperm whales usually dive between 300 and 800 meters, and sometimes 1 to 2 kilometers.
Such dives can last more than an hour. They feed on several species, especially giant squid, but also colossal squid, octopus and fish such as demersal rays and sharks, but their diet is mainly medium-sized squid. Some prey may be accidentally caught while eating other items. Most of what we know about deep-sea squid has been learned from specimens in the stomachs of captured sperm whales, although more recent studies have analyzed feces. One study, conducted in the Galapagos, found that squid from the Histioteuthis (62%), Ancistrocheirus (16%), and Octopoteuthis (7%) genera weighing between 12 and 650 grams (0.026 and 1.433 lb) were the most commonly consumed.
Battles between sperm whales and giant squids or colossal squids have never been observed by humans; however, the white scars are believed to be caused by large squid. A study published in 2010 gathered evidence suggesting that female sperm whales may cooperate when hunting Humboldt squid. Tagging studies have shown that sperm whales hunt upside down on the bottom of their deep dives. It is suggested that these specimens can see the squid silhouetted above them against the dim surface light.
Sperm whales sometimes take long-lined cod. Longline fishing operations in the Gulf of Alaska complain that sperm whales take advantage of their fishing operations to eat desirable species
Furthermore, it has also been noted that sperm whales feed on bioluminescent pyrosomes such as Pyrosoma atlanticum. It is thought that sperm whales’ foraging strategy for bioluminescent squid may also explain the presence of these light-emitting pyrosomes in the sperm whale’s diet.
The sharp beak of a consumed squid lodged in the whale’s intestine can lead to the production of ambergris, similar to the production of pearls in oysters. Intestinal irritation caused by squid beaks stimulates the secretion of this lubricant-like substance. Sperm whales are prodigious feeders, eating about 3% of their body weight per day. The total annual consumption of prey by sperm whales worldwide is estimated to be approximately 91 million tonnes. In comparison, human consumption of seafood is estimated at 115 million tons.
Sperm whales hunt by echolocation. Their clicks are among the loudest sounds in the animal kingdom.
According to a 2003 National Geographic article, the sperm whale is the loudest animal in the world. Sperm whale pops have an emission level exceeding 230 dB at a pressure of one micropascal and a distance of one meter.
It has been hypothesized that it can stun prey with its clicks. Experimental studies attempting to reproduce this effect have been unable to replicate the supposed lesions, casting doubt on this idea.
It has been argued that sperm whales, as well as other large cetaceans, help fertilize the ocean surface by consuming nutrients in the depths and transporting those nutrients to the surface of the oceans when they defecate, an effect known as the whale pump.
This fertilizes phytoplankton and other plants on the ocean surface and contributes to ocean productivity and atmospheric carbon reduction.
As regards breathing and diving, sperm whales, together with pilot whales and elephant seals, are the marine mammals that dive to the greatest depths.
They are believed to be capable of reaching up to three kilometers below the surface and diving for up to 90 minutes. However, the most common thing is that they descend to a distance of 400 meters in dives lasting 35 minutes. On these huge dives they run the risk of drowning if they get trapped in underwater cables.
The sperm whale adapts perfectly to the enormous changes in pressure when submerged. Their rib cage is very flexible, allowing the lungs to collapse, reducing nitrogen entry into the tissues, and the metabolism can slow down to conserve oxygen. Myoglobin, a protein that stores oxygen in muscles, is much more abundant than in land animals. Blood has a high density of red blood cells, which contain hemoglobin, which transports oxygen. Oxygenated blood can be directed to the brain and other essential organs only when oxygen levels decrease. Even the spermaceti organ, i.e. the oily-waxy substance found in an external concavity of the skull of Physeterid cetaceans, can play a role in regulating the buoyancy.
Between dives, the sperm whale breathes for about eight minutes before the next dive. Like other toothed whales, they breathe through a single “S”-shaped spiracle. They breathe three to five times per minute at rest, increasing to six to seven times per minute after a dive. The shot is unique and loud, with a jet that rises up to fifteen meters from the surface and points forward and to the left at an angle of 45°. On average, females and juveniles breathe every 12.5 seconds before diving, while large males breathe every 17.5 seconds before diving.
Sperm whales breathe air at the surface of the water through a single s-shaped blowhole. The blowhole is located on the left side of the front of the enormous head. They breathe 3-5 times per minute at most, but the number increases to 6-7 times per minute after a dive. The puff is a single noisy jet that rises up to 15 m above the surface of the water and is inclined forward, to the left of the cetacean, at an angle of 45°.
As for its predators, the only one that attacks sperm whales, besides humans, is the orca. Large roving pods of orcas frequently attack groups of females with calves, usually attempting to separate the sperm whale calf and kill it. Female sperm whales can often repel these attacks by forming a circle with their babies in the center and then violently flapping their tails, thus preventing the orcas from penetrating the formation. If the pod of orcas is extremely large, they can sometimes kill even adult females. The large male sperm whales, however, have no predators, because even killer whales can be killed by these aggressive and powerful creatures.

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– GBIF, the Global Biodiversity Information Facility.
– Louisy P., 2016. Guide to the identification of marine fishes of Europe and the Mediterranean. Il Castello Editore, Milan.
– Nikiforos G., 2008. Fauna of the Mediterranean. Giunti Editore, Florence.

Photo source:
– https://www.inaturalist.org/taxa/74890-Physeter-macrocephalus/browse_photos