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Dwarf Sperm Whale
The dwarf sperm whale (Kogia sima) is a part of the sperm whale family of the genus Physeter. It is rare to see them, since they share morphological characteristics to the pygmy sperm whale and are small cetaceans. Most information of dwarf sperm whales has been from data collected from coastal strandings .
Taxonomy
Dwarf sperm whales are classified in the family Kogiidae and the genus Kogia. Originally, this species was thought to be categorized in the family Physeteridea and the superfamily Physeteroidea. It wasn't until 1966 that the dwarf sperm whale and the pygmy sperm whale were classified as their own family, Kogiidae.
Description
The dwarf sperm whale is the smallest cetacean. Morphological descriptions from sightings are rare and most information is collected from autopsies after strandings. They grow up to 2.7 meters (8.9 feet) in length and weigh up to 250 kilograms (550 pounds)[1]. They have no records of sexual dimorphism [2].
The skull of the dwarf sperm whale, like Odontocetes, is asymmetrical. The left naris is notably larger[2] than the other which is for echolocation. Their skull also does not have an independent jugal bone, does have a supra cranial basin and a sagittal septum.
From field observations, at the surface the back of the whale is more flat from the anterior to the fin[1]. The dorsal itself is in the middle of the dorsal line, unlike the pygmy sperm whale which has the dorsal line closer to it tail[1]. Their bodies are compacted and streamlined[3].
As for free range clicks they have a usual Odontocete click, which means peaks ad centroid of 127-129 kHz [4]. The mean range of the clicks is -3 dB and -10 dB bandwidth of 10 and 16-17 kHz[4].
Diet
The diet of the dwarf sperm whales consists squid and crab. The prefer feeding on the shelves and shelf edges [3]. It has also been recorded that they forage in deep waters from dietary evidence from beach strandings[3].
Behavior
Dwaft sperm whales are rarely engage in active behavior and remain motionless at the surface of the water to avoid detection[3]. From observation in the field, they take long and deep dives[3].
Population & Distribution
Dwarf sperm whales are pelagic whales and found in warm temperate and tropical waters of the Atlantic, Indian and Pacific Ocean[3]. It has been observed that juvenile whales spend time at the upper portion of the shelf and the adults tend to stay in deeper waters[2].
Life Cycle
Dwarf sperm whales are rare, making their mating systems a mystery [5]. Their gestation period is roughly 9 to 11 months. Their calving season is at least 5 to 6 months and calving peaks during the summer months[5].
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References
- ^ a b c Bonato, Marc; Webber, A. Marc; Attoumane, Artadji; Giacoma, Cristina (2016). ""First records of dwarf sperm whale (Kogia sima) from the Union of the Comoros."" (PDF). Marine Biodiversity Records. 9. doi:10.1186/s41200-016-0064-z. S2CID 5014340.
{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link) - ^ a b c Willis, M. Pamela; Baird, W. Robin (1998). "Status of the Dwarf Sperm Whale, Kogia simus, with Special References to Canada" (PDF). Retrieved 23 May 2018.
{{cite web}}: CS1 maint: multiple names: authors list (link) - ^ a b c d e f Mcalpine, Donald F. (2009). "Pygmy and Dwarf Sperm Whales: Kogia breviceps and K. sima". Encyclopedia of Marine Mammals. 2nd Edition: 936–938. doi:10.1016/B978-0-12-373553-9.00212-1.
- ^ a b Merkens, P.B. Karlina; Mann, David; Janik, M. Vincent; Claridge, Diane; Hill, C. Marie; Oleson, Erin (February 2018). "Clicks of dwarf sperm whales (Kogia sima)". Research Gate.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ a b "Kogia sima (dwarf sperm whale)". Animal Diversity Web. Retrieved 2018-06-07.