Dwarf sperm whale

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Dwarf sperm whale[1]
Temporal range: Pliocene – Recent
↓
[2]
Size compared to an average human

Least Concern  (IUCN 3.1)[3]
CITES Appendix II (CITES)[4]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Kogiidae
Genus: Kogia
Species:
K. sima
Binomial name
Kogia sima
(Owen, 1866)[3]
Dwarf sperm whale range
Synonyms[5]
  • Kogia simus Owen, 1866
  • Physeter (Euphyseter) simus Owen, 1866
  • Callignathus simus Gill, 1871

The dwarf sperm whale (Kogia sima) is a

synonymous with the pygmy sperm whale (Kogia breviceps) from 1878 until 1998. The dwarf sperm whale is a small whale, 2 to 2.7 m (6 ft 7 in to 8 ft 10 in) and 136 to 272 kg (300 to 600 lb), that has a grey coloration, square head, small jaw, and robust body. Its appearance is very similar to the pygmy sperm whale, distinguished mainly by the position of the dorsal fin
on the body–nearer the middle in the dwarf sperm whale and nearer the tail in the other.

The dwarf sperm whale is a

killer whale (Orcinus orca) and large sharks such as the great white shark (Carcharodon carcharius). When startled, the whale can eject a cloud of red-brown fluid. Most of what is known of the whale comes from beached individuals, as sightings in the ocean are rare. Many of these stranded whales died from parasitic infestations or heart failure
.

The dwarf sperm whale is hunted in small numbers around Asia. It is most threatened by ingesting, or getting entangled by marine debris. No global population estimate has been made, and so its conservation status by the International Union for Conservation of Nature (IUCN) is least concern.

Taxonomy

Dwarf sperm whale skull

The first two dwarf sperm whale

species name simus is Latin for "stump-nosed", a reference to its blunt snout. John Edward Gray, when he created the genus Kogia in 1846, gave no indication to the meaning, but, since the word has a feminine ending, the masculine species name simus had to be changed to sima to fit this when the combination Kogia simus was proposed by various 20th century authors.[7][8] In 1900, zoologist Frank Evers Beddard speculated that the word "might be a tribute to a Turk of the past surnamed Cogia Effendi, who observed whales in the Mediterranean".[9]

In 1871,

mammalogist Graham James Berry Ross from 1979.[14]

Genetic testing in 2006 suggests that K. sima may actually represent two species, one in the Atlantic and one in the Indo-Pacific region. The Cape of Good Hope around South Africa may mark the barrier between these two populations.[15][16]

Description

Size comparison between the sperm whale (blue), the pygmy sperm whale (green), and the dwarf sperm whale (orange)

The dwarf sperm whale can range in size from 2 to 2.7 m (6.6 to 8.9 ft) in length and 136 to 272 kg (300 to 600 lb) in weight—less than the 4.25 m (14 ft) and 417 kg (920 lb) pygmy sperm whale. A newborn is generally around 1 m (3 ft 3 in) long and 14 kg (31 lb). Males are thought to reach physical maturity at age 15, and females at age 13. Sexual maturity, which happens after an individual has attained 2–2.2 m (6 ft 7 in – 7 ft 3 in) in length, happens at 2 to 3 years for males and around 5 for females.[17][7][18] Gestation takes place probably over around 9.5 months.[7]

The dwarf sperm whale has a dark-grey or blue-grey coloration with a lighter-grey underside, and a pale, crescent-shaped mark between the eye and the flipper, sometimes called a "fake gill", which is characteristic of the genus. Some individuals have been known to have a second crescent-shaped mark, creating a sort of pale ring encircling a darker spot. It has a high dorsal fin halfway down the length of the body, and two or more throat grooves. The dorsal fin is taller and closer to the head than it is in the pygmy sperm whale, and the back is flatter.[16][17][19]

Museum model of a dwarf sperm whale

Kogia is identified as having a square head, a small jaw with the snout jutting outward, and a porpoise-like build with a robust body that rapidly decreases towards the tail. They have the shortest snouts of any modern day whale. Characteristic of sperm whales, the left nostril is markedly larger than the right, and it has a spermaceti organ on its skull.[17] The brain weighs around 0.5 kg (1.1 lb).[20] The eyes are adapted for low-light environments. The dwarf sperm whale has 14 to 24 teeth, rarely 26, in the lower jaw that are sharp, slightly curved backwards, and–like other sperm whales–lack enamel. The teeth rarely exceed 30 mm (1.2 in) in length, smaller than those of the pygmy sperm whale. At most, 6 teeth are in the upper jaws, though in modern sperm whales, upper teeth are defunct.[17]

Unique to Kogia, there is a sac which hangs off from the

sexually dimorphic.[17][19]

Population and distribution

The dwarf sperm whale ranges throughout tropical and temperate oceans of the world and inhabits the continental shelf and slope area.[16] It seems to prefer warmer waters than the pygmy sperm whale. The dwarf sperm whale is one of the most commonly beached deep-diving whales in the world, though rarely seen at sea, and likewise, most information about the whale comes from examining beached individuals. Diving depth may vary from place to place: a study in the Bahamas placed average depth at around 250 m (820 ft), whereas a study in the deeper waters of Hawaii placed it at around 1,500 m (4,900 ft).[21]

In the West Pacific, its recorded range spans from Japan to Tasmania and New Zealand, and in the East Pacific from British Columbia to central Chile. In the Indian Ocean, the whale is reported from Oman, Sri Lanka, India, Thailand, Philippines, Indonesia around Timor, western Australia and South Africa. In the West Atlantic, it has been recorded from Virginia to southern Brazil, and in the East Atlantic from Italy in the Mediterranean Sea to South Africa.[17]

No global population estimation has been made. Population counts have been taken over certain areas, though given the difficulty to distinguish the dwarf sperm whale from the pygmy sperm whale, the overall estimate represents the total number of both species. In the North Atlantic, they are estimated at around 3,785 individuals;[22] in the East Pacific, around 11,200 individuals.[7]

Ecology

elongate jewel squid
(Histioteuthis reversa) is a common prey item.

Diet

The dwarf sperm whale is an

elongate jewel squid (Histioteuthis reversa) and Taonius.[23]

The throat grooves and the developed musculature in the throat in Kogia are probably adaptations for increasing the volume of the mouth for

suction feeding, possibly the best-developed among toothed whales. Also, the blunt snout, lack of teeth, and reduced jaw are characteristics seen in other suction feeding toothed whales. The whale uses its sharp teeth to hold onto prey while expelling water from the mouth.[24]

Dwarf sperm whale calves typically start eating solid food once they have reached a size of around 1.35 m (4 ft 5 in) though are not fully weaned until they reach around 1.5 m (4 ft 11 in). Toothed whale calves generally start eating solid food at around 6 months, and mothers stop lactating after around 18 to 20 months.[7]

Threats

cestode Phyllobothrium delphini in beached individuals indicates shark attacks since the cestode matures in sharks.[7]

The dwarf sperm whale also competes with other squid-eating whales, such as beaked whales. It occupies the same ecological niche in the same regions as the pygmy sperm whale, though the latter can forage in deeper waters and has been known to feed on a wider array of species of larger size.[21][23]

Some beached individuals have had large parasitic infestations which probably lead to their death, particular with

tapeworms in the blubber. In the southeastern United States, stranded dwarf sperm whales were found to have died from heart failure, and heart failure may have led to the stranding itself.[7][25]

Behavior

Dwarf sperm whales tend to float only near the surface.

Kogia is thought to be slow-moving, rarely displaying rapid

surfacing behavior, tending to float at the surface with only the nape and dorsal fin exposed. From the surface, they sink vertically, instead of lifting their tails out of the water to dive, which would create a splash.[17]

The dwarf sperm whale congregates into small pods of one to four individuals, though on occasion up to ten, likely due to limited food resources. Small group size and deep foraging grounds in the summer could also be anti-predator behaviors. However, this is less likely as dolphins congregate in large pods with hundreds of members to prevent predation. The whale probably follows seasonal squid migrations from offshore in the summer to nearshore in the winter. It is possible it prefers a slope habitat as it allows the whale to herd squid against the wall, or it causes upwelling which the whale can ride on in order to save energy while hunting.[16][21][26] Younger animals may congregate in shallower areas and adults in deeper areas; the slope around South Africa may be a nursery grounds.[7]

Kogia, unlike other whales, can eject a red-brown fluid when startled, likely to distract predators, similar to squid. This cloud can cover 100 m2 (1,100 sq ft) in the water.[17]

This species does not whistle, and instead produces

frequencies of Kogia are generally less than 130 kHz.[27]

Relationship with humans

There is some hunting of the dwarf sperm whale in Indonesia, Japan, Sri Lanka, and the Lesser Antilles as food or bait, though there are no major operations. A bigger threat is likely ingestion of marine debris and entanglement in fishing gear, though it has not been determined how serious a threat these pose.[28][7] The International Union for Conservation of Nature (IUCN) currently lists the dwarf sperm whale's conservation status as data deficient, though it could possibly be of least concern.[3]

The dwarf sperm whale is covered by the

Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area.[29] The species is further included in the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU),[30] and the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).[31]

See also

References

  1. OCLC 62265494
    .
  2. ^ "Kogia sima". Fossilworks. Gateway to the Paleobiology Database. Retrieved 8 March 2024.
  3. ^
    doi:10.2305/IUCN.UK.2020-2.RLTS.T11048A50359330.en
    . Retrieved 19 November 2021.
  4. ^ "Appendices | CITES". cites.org. Retrieved 2022-01-14.
  5. ^ a b Perrin WF, ed. (2009). "Kogiidae". World Cetacea Database. World Register of Marine Species. Retrieved 6 August 2018.
  6. doi:10.1111/j.1096-3642.1866.tb00570.x
    .
  7. ^ a b c d e f g h i j Plön, Stephanie (January 2004). The Status and Natural History of Pygmy (Kogia breviceps) and Dwarf (K. sima) Sperm Whales off Southern Africa (PDF) (Thesis). Rhodes University.
  8. ISBN 978-1-891276-03-3
    .
  9. ^ Frank Evers Beddard (1900). A Book of Whales. London, J. Murray; New York, G.P. Putnam's Sons. p. 186.
  10. S2CID 84450779
    .
  11. ^ Ogawa, T. (1936). "Studien über die Zahnwale in Japan" [Studies on the Toothed Whales in Japan]. Mitteil: Botany & Zoology (in Japanese). 4: 2017–2023.
  12. ^ Yamada, M. (1954). "Some Remarks on the Pygmy Sperm Whale, Kogia" (PDF). Scientific Reports of the Whales Research Institute. 9: 37–58.
  13. ^ Handley, C. O. (1966). "A Synopsis of the Genus Kogia (pygmy sperm whale)". In Norris, K. S. (ed.). Whales, Dolphins, and Porpoises. University of California Press. pp. 62–69.
  14. ^ Ross, G. J. B. (1979). Records of Pygmy and Dwarf Sperm Whales, Genus Kogia, from Southern Africa, with Biological Notes and Some Comparisons. Annals of the Cape Provincial Museums Natural History. Cape Provincial Museums. pp. 1–60.
  15. doi:10.1111/j.1748-7692.2005.tb01255.x
    .
  16. ^
    ISBN 978-0-08-091993-5
    .
  17. ^ a b c d e f g h i Willis, P. M.; Baird, R. W. (1998). "Status of the dwarf sperm whale, Kogia simus, with special reference to Canada" (PDF). Oceanographic Literature Review. 112 (1): 114–125.
  18. JSTOR 3503937. Archived from the original
    (PDF) on 2016-03-04. Retrieved 2013-08-01.
  19. ^
    S2CID 5014340
    .
  20. PMID 12892406
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  21. ^
    doi:10.25148/etd.fi15101248. {{cite journal}}: Cite journal requires |journal= (help
    )
  22. doi:10.7289/V5/TM-NEFSC-241
    . NMFS-NE-241.
  23. ^
    doi:10.1111/mms.12064
    .
  24. S2CID 6949085
    .
  25. PMID 4077624
    .
  26. ^ Bermúdez Villapol, A Luis; Sayegh, Alejandro; León, Tatiana (2008). "Notes on the confirmation of the Dwarf sperm whale Kogia sima Owen, 1866 (Cetacea: Kogiidae) on Venezuelan coasts". Revista Científica UDO Agrícola. 8 (1): 154–162 – via Bioline.
  27. hdl:10023/17127
    .
  28. ISBN 978-2-8317-0656-6
    .
  29. ^ "Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area" (PDF). 1996. Archived from the original (PDF) on 2017-09-18. Retrieved 2018-08-13.
  30. ^ "Kogia sima". Convention on the Conservation of Migratory Species of Wild Animals.
  31. ^ "Diversity Database". Pacific Cetaceans Memorandum of Understanding. Archived from the original on 2012-03-31.

Further reading

External links

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