Sperm whale
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetartiodactyla
Infraorder: Cetacea
Parvorder: Odontoceti
Famiglia: Physeteridae
Genus: Physeter
Species: Physeter macrocephalus (Linnaeus 1758)
Description
The sperm whale is the largest of the odontocetes, with an average length of 18 meters and a weight of 50 tons. The female is smaller in size (about 11 meters).
Characteristic of the species is the profile of the enormous head. The coloration is uniformly dark gray; along the outside of the upper jaw and mandible, the skin is white. The blowhole is at the end of the head, displaced to the left side, and the blowhole is low, disordered, and directed obliquely forward at an angle of about 45°.
Dives reach up to 3,000 meters. Before diving, the sperm whale remains at the surface for about 10 minutes, then arches its back showing its large tail.
Of pelagic habits, the sperm whale approaches the coast only where it has a steep bottom. This species is cosmopolitan; in Italy, it is found in both the Ligurian and Tyrrhenian Seas.
The sperm whale feeds on mesopelagic cephalopods, barracuda tuna, and demersal species such as cod, hake, and medium- and large-sized weveers.
Mediterranean Conservation Status
In 2012, the Mediterranean sperm whale subpopulation was listed as Endangered on the IUCN Red List due to the population's numerical decline and the small number of adult individuals.
Sperm whale numbers in the Mediterranean are alarming; the population is down to a few hundred individuals.
Threats include catches in fishing gear (particularly drift nets, still used in the central and eastern Mediterranean) and collisions. In addition, the population is disturbed by heavy maritime traffic. The combination of these factors is likely to have led to a decline (of unknown magnitude) over the past half-century, and in the absence of effective management to mitigate ongoing threats, the population decline is likely to continue.
Listed in
CMS App. I, App. II
CITES App. I
Bern Convention App. II
Barcelona Convention, SPA/BD Protocol, Annex II
EU Habitats Directive: Annex IV
Global status
Vulnerable
The local population
The presence of sperm whales in the study area has been monitored since 1991. Since 2004, thanks to the development of the acoustic detection system, the number of sightings has increased significantly.
Sperm whale residence and movements in the study area were studied regularly through photo-identification data collected over 20 years (2003-2022).
A total of 104 individuals were photo-identified on the basis of natural marks on the caudal fin. The recruitment rate of sperm whale individuals into the photo-identification catalog varies irregularly over the years, suggesting that the waters of Ischia represent only part of the population's home range and that the area is exploited by different groups, and that the number of specimens to be cataloged is still large.
The data show that the study area is frequented by all the different aggregations and age classes of the species, with groups composed of females and immatures, solitary males, and pods of young males.
Finally, it is relevant that a stable association between young males has been documented over time. This type of association is little known, and stable associations among immature males had not previously been reported. The association that we have recorded over the years suggests that the social structure of groups of nonreproductive males may reflect that of females in terms of complexity and long-term relationships among individuals.
Thanks to the data collected by our organization on this species, the Pontine Campanian Archipelago has been recognized as a Important Marine Mammal Area (IMMA) by the IUCN Marine Mammal Protected Areas Task Force.
Sperm whales have been observed mainly in the deep central head of the submarine canyon of Cuma and southwest of Ischia. Some sightings have also been made in the Magnaghi and Dohrn canyons (southeast, and east of Ischia, respectively).
The distribution of sperm whales in the area has a strong association with submarine canyon waters, in an area of about 20-40 km in diameter.
Acoustics
Sperm whales emit signals called clicks, which are broad-band frequency and directional, with energy between 5 and 25 kHz. These sounds are used for echolocation and communication. The clicks can be very powerful, up to 223 dB re 1µPa / 1m, the most intense biological source ever recorded.
Normally, the sperm whale emits regular sequences of clicks (usual clicks) with which it explores the environment in search of potential prey.
Sometimes, the clicks change rate, accelerating to an interval of between 5 and 100 milliseconds from one click to the next. In this case, the vocalization is called a creak and can be emitted either at depth or at the surface. During the dive phase, the acceleration of clicks is interpreted as the sperm whale's attempt to focus on its identified prey and is therefore used as an index of feeding activity.
Spectrogram of coda-creaks of sperm whale
Creaks emitted at the surface appear to have a shorter duration and a more constant interval between clicks; depending on the authors, they have been termed coda-creaks or chirrups. They have been described as social sounds; however, whether they are used for echolocation or communication remains unclear.
The most intriguing vocalization of this species is the so-called codas, stereotyped patterns of clicks whose function could be to communicate through the patterns and rhythms of click sequences. They seem to be signals used within groups rather than to communicate between one group and another; they have a very low emission intensity.
Spectrogram of sperm whale codas
Cultural transmission has been described for codas: some social units share an acoustic repertoire (dialect) that allows them to be classified into clans. Clans are sympatric (share the same territory), can contain thousands of sperm whales, and be distributed over thousands of kilometers. The acoustic repertoire of codas is culturally transmitted within the smallest module of sperm whale social structure, the social unit or family group composed of adult females and immature individuals of both sexes. Several patterns of codas have been recorded in the oceans.
Some types of codas appear to be common to different areas, and for a long time it was believed that the (3+1) pattern was the only existing type in the Mediterranean, although, on a few occasions, other codas were recorded. In the study area, the 3+1 pattern codas is well represented, however, the presence of several different patterns, suggests a more diverse repertoire.
