Kogia sima

Kogia sima

Dwarf sperm whale (Kogia sima Owen, 1866) is a cetacean belonging to the Physeteridae family.

Systematic –
From a systematic point of view it belongs to:
Eukaryota domain,
Kingdom Animalia,
Phylum Chordata,
Mammalia class,
Order Cetacea,
Suborder Odontoceti,
Physeteridae family,
Genus Kogia,
Species K. Sima.
The term is basionym:
– Physeter simus Owen, 1866.
The term is synonymous:
– Callignathus simus Gill, 1871.

Geographic Distribution and Habitat –
The Kogia sima is a cetacean present in tropical and temperate oceans throughout the world, especially near the continental shelf and slope.
This species is present in the western Pacific from Japan to Tasmania and New Zealand, while in the eastern Pacific the range extends from British Columbia to central Chile. In the Indian Ocean it has been reported in the waters of Oman, Sri Lanka, India, Thailand, Indonesia (Timor), Western Australia and South Africa. In the Atlantic the species can be found from Virginia to southern Brazil in the western part and from Italy (Mediterranean Sea) to South Africa in the eastern part.
Its favorite marine habitat is deep water but most of the information we have comes from the examination of stranded individuals. The depth of dives can vary from one place to another: during a study in the waters of the Bahamas the average depth of dives was found to be 250 m, while in the deeper waters around Hawaii these animals descend on average to around 1500 m.
It is possible that this species prefers continental slopes because in this type of habitat it could gather squid against the wall or because in these areas the phenomenon of upwelling occurs, which the animal can exploit to save energy during hunting. Younger specimens may also gather in shallower waters and adults in deeper ones; the continental slope around South Africa could provide a breeding ground.

Description –
The Kogia sima is a cetacean measuring 2-2.7 m in length and weighing 136-272 kg and does not present sexual dimorphism.
At birth it measures approximately 1 m in length and weighs 14 kg. Males are believed to reach maximum size at the age of 15 and females at 13.
Its color is dark gray or bluish-grey, with the underside of a lighter gray and a pale, crescent-shaped mark between the eye and the pectoral fin, sometimes called “false gill”, characteristic of the genus to which belongs. Some individuals have a second false gill that creates a sort of light ring surrounding a darker spot. The species also has a pronounced dorsal fin, located near the center of the back, and two or more grooves on the throat. The dorsal fin is higher and closer to the head than that of Kogia breviceps, furthermore the profile of the back is flattened.
It has a significantly larger left nostril than the right and a spermaceti organ in its head. The brain weighs about 0.5 kg. The eyes are adapted to low light conditions.
This cetacean has 14 to 24 teeth, rarely 26, on the lower jaw, slightly curved backwards and without enamel. In some specimens up to 6 teeth can be found on the upper jaw, a unique case in modern physeterids.
A peculiar characteristic is the presence of a sac located in the lower part of the large intestine, near the anus, filled with a thick reddish-brown fluid similar to chocolate syrup, which is released when the animal is stressed.
It also has 50 to 57 vertebrae – 7 cervical vertebrae, 12-14 thoracic vertebrae and 29 or 35-37 lumbar vertebrae. The variation in number may be due to bone loss during the preparation of museum specimens or simple individual variability.
Finally, as regards the sounds emitted, these cetaceans do not whistle, but produce high-frequency narrow-band clicks. These clicks are more reminiscent of those emitted by some species of dolphins and porpoises, such as Lagenorhynchus cruciger, Cephalorhynchus hectori, Cephalorhynchus eutropia, Cephalorhynchus commersonii, Phocoena phocoena and Phocoenoides dalli.
Cogia peak frequencies are generally below 130 kHz.

Biology –
The Kogia sima reaches sexual maturity when an individual measures 2-2.2 m in length and is reached at 2-3 years in males and 5 in females.
Little information is known about the reproduction of this species. It is likely that the mating process is similar to that of other cetaceans: when both females and males line up belly to belly, the male inserts his penis into the female’s genital canal and fertilization occurs internally. The gestation period is 9.5 months and the length of the calving season appears to last at least 5 or 6 months. There appears to be at least a peak in births during the summer months. Frequent observations of pregnant females accompanied by unweaned pups suggest an annual reproductive cycle with one newborn per year.
The hatchlings typically begin eating solid food once they reach a size of about 1.35 m, although they are not fully weaned until they reach about 1.5 m. Babies generally start eating solid food around 6 months and mothers stop breastfeeding after around 18-20 months.

Ecological Role –
The Kogia sima is a cetacean that inhabits temperate and tropical oceans throughout the world, particularly near continental shelves and margins.
It was first described by the biologist Richard Owen in 1866 based on illustrations made by the naturalist Sir Walter Elliot, but was considered a synonym of Kogia breviceps from 1878 to 1998.
This cetacean is a predator that feeds by “suction” mainly on squid and lives in small schools of 1-4 specimens. In turn it is preyed upon by killer whales (Orcinus orca) and larger sharks, such as the white shark (Carcharodon carcharias). When frightened, it may emit a reddish-brown fluid from its anus, similar to a squid. Most of what we know about this species comes from examining stranded specimens, since sightings at sea are rare. Many of these stranded animals die from parasitic infections or heart failure.
The stomachs of stranded specimens contain mainly squid and, in smaller numbers, deep-sea fish (from the mesopelagic and bathypelagic zones) and crustaceans. However, crustaceans make up a sizable portion – up to 15% – of the diet of Hawaiian cogia. The stomach contents of specimens stranded in various regions of the globe indicate a preference for squid from the Histioteutid and Cranchiid families, in particular for Histioteuthis reversa and Taonius.
Predators include killer whales (Orcinus orca) and sharks. Remains attributed to this species were found in the stomachs of white sharks (Carcharodon carcharias) and the infestations of the tapeworm Phyllobothrium delphini found in some stranded specimens indicate that they had been attacked by sharks, since this species of tapeworm matures precisely in these latter animals .
The Kogia sima competes with other cetaceans that feed on squid, such as beaked whales, and occupies the same ecological niche as the de Blainville’s cogia in areas where the ranges of the two species overlap, even if the latter is able to feed in deeper waters and feeds on a wider range of larger prey.
This cetacean is hunted on a small scale in Indonesia, Japan, Sri Lanka and the Lesser Antilles for its meat, which is consumed or used as bait to catch other animals. A far more serious threat is posed by ingesting plastic and becoming entangled in fishing nets, although the extent to which the population is threatened by this has not yet been determined. The International Union for Conservation of Nature (IUCN) currently considers its conservation status to be “insufficiently known” (Data Deficient), but it is likely that it should be included among the “species of least concern” (Least Concern).
It is protected by the Convention on International Trade in Endangered Species (CITES) and the Agreement on the Conservation of Cetaceans in the Black Sea, the Mediterranean Sea and Contiguous Atlantic Areas. The species also appears in the Memorandum of Understanding on the Conservation of the Manatee and Small Cetaceans of West Africa and Macaronesia (West African Aquatic Mammals Memorandum of Understanding) and in the Memorandum of Understanding on the Conservation of Cetaceans of the Pacific Islands (Pacific Islands Cetaceans Memorandum of Understanding).
Furthermore, an overall estimate of the population has never been carried out and the censuses carried out concern only limited areas; furthermore, given the difficulty of distinguishing Owen’s cogia from de Blainville’s, the estimates evaluated concern the total number of both species. In the North Atlantic, estimates indicate the presence of around 3,785 individuals and around 11,200 in the eastern Pacific.

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://inaturalist-open-data.s3.amazonaws.com/photos/289877131/original.jpg
– https://www.researchgate.net/figure/Dwarf-sperm-whale-Kogia-sima-Illustration-by-Martin-Camm_fig1_267306662