Species

Dwarf sperm whale

April 15, 2011, 7:22 pm
Content Cover Image

Dwarft sperm whale. Source: WWF/Lory Tan

The Dwarf sperm whale (scientific name: Kogia sima) is one of two species of cetaceans in the family  Kogiidae, the other being the Pygmy sperm whale. As their names suggest they are small compared to their distant cousin the Sperm whale. Like sperm whales, their mouth is on the underside of their body, but unlike Sperm whales they have very few and very small teeth that are sharply pointed and curved. Like Sperm whales, they are suction feeders and eat mostly squid. Knowledge about these species has been slow to accumulate, and in fact, the existence of the two species only became widely accepted in 1966

caption Dwarf Sperm Whale (Kogia sima) Source: NOAA
caption Size comparison of an average human and a dwarf sperm whale (Kogia sima). Source: Chris Huh

Conservation Status
Data deficient

Scientific Classification

Kingdom: Anamalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Cetacea (Cetaceans)
Family:-------- Kogiidae
Genus:---------- Kogia
Species:----------- Kogia sima (Owen, 1866)

Common Names:
Cachalote enano
Cachalote anão
Dwarf sperm whale
Ogawa komakko kujira
Snub-nosed cachalot  

The Dwarf sperm whale is similar to the Pygmy sperm whale, but is smaller and has a larger, taller dorsal fin, higher on its back, that looks like the dorsal fin of a bottlenose dolphin. Dwarf sperm whales live in small social groups. There are groups of females with calves; groups of males and females without calves; and groups of young whales who are not yet sexually mature. A form of defensive behavior called inking has been seen in both species of Kogia. To escape danger, the whale excretes a cloud of reddish-brown feces and then dives out of sight. Most other information has come from dissecting individuals who stranded and died. Squid, fish, crustaceans - and plastic bags - have been found in their stomachs.

There is some evidence that the Dwarf sperm whale may, in fact, be two species, one in the Atlantic Ocean and one in the Indian and Pacific Oceans.

Physical Description

Prominent morphological features include endothermism and bilateral symmetry. The Dwarf sperm whale has a porpoise-like form, with the blowhole positioned on the left side of the forehead, and a shark-like mouth posterior to the snout. The skull is asymetrical. The greatest girth of the body is between the dorsal and pectoral fins. The skin is a steel- gray color with a white ventrum. Some individuals have pink or purplish blotches on their venters. The head and body measure 2.1 to 2.7 meters (m). The pectoral fin is 40 centimeter (cm) high, and the expanse of the flukes is 61 cm. The head is one sixth of the entire length of the animal. The facial part of the skull is the shortest of any cetacean. The large teeth are sharp and curved, and they are present in the lower jaw only. Small non-functional teeth may be present in the upper jaw. Body mass of an adult typically ranges from 136 to 272 kilograms.

Behavior

Key behaviors of this marine mammal are: natatorial; motile; social. Dwarf sperm whales are reported to be sluggish creatures, often seen floating around on the surface of the water close to shore. They are typically social. Groups of ten or fewer animals are normal. Sexually mature males and females are found in the same groups, and there is some evidence that immatures form their own groups. Intraspecific fighting has been reported, but the nature of these conflicts is not known. 

Reproduction

Key reproductive features are: gonochoric/gonochoristic/dioecious (sexes separate); sexual; viviparous. Liitle is known about the reproductive cycle of this rare whale. Males and females become sexually mature at lengths of 2.1 to 2.2 meters. Gestation is approximately nine months, and there appears to be a calving season that lasts four to five months. Females are typically seen in association with only one calf, indicating that single births are the norm. Calves are approximately one meter long at birth. Interestingly, the body proportions of these animals do not change as the calves mature.

Distribution and Movements

The IUCN Red List notes that there "is considerable uncertainty about the status of this species, which may span a range from Least Concern to a more threatened category. It is fairly abundant but there is no information on trends in global abundance. This species is potentially vulnerable to low-level threats and a 30% global reduction over three generations (36 years; Taylor et al. 2007) cannot be ruled out."

Habitat

Although Dwarf sperm whales spend most of their time at the surface of the water near the shore, they forage at great depths.

Feeding Habits

The shape and position of the mouth indicate that this whale may feed very near the ocean floor; correspondingly, the Dwarf sperm whale feeds atconsiderable sea depths, reaching the ocean floor. The diet of this species consists mainly of cephalopods, fish and crustaceans found at depths of 250 to 1300 meters; moreover, mollusks are also common prey.

Economic Importance for Humans

This whale is too rare to have any real economic importance to humans. However, researchers have suggested that the rarity of these sluggish animals may be due overharvesting of populations in the past.

Threats and Conservation Status

The IUCN Red List notes that there "is considerable uncertainty about the status of this species, which may span a range from Least Concern to a more threatened category. It is fairly abundant but there is no information on trends in global abundance. This species is potentially vulnerable to low-level threats and a 30% global reduction over three generations (36 years; Taylor et al. 2007) cannot be ruled out."

Further:

No estimates of global abundance exist. Abundance is often underestimated using visual survey methods because they dive for long periods and are inconspicuous when they surface (Barlow 1999). Delineations between stocks are often difficult to determine, therefore assessments should be considered ongoing processes. In the case of the Dwarf sperm whale, concern that sightings may be confused with or for the congener K. breviceps (the Pygmy sperm whale) further complicates interpretation of past estimates of abundance.

There are estimated to be about 19,172 (CV=66%) off Hawaii (Barlow 2006); 742 of both species of Kogia (CV=29%) in the northern Gulf of Mexico (Mullin and Fulling 2003); 395 of both species (CV=40/75%) in the western North Atlantic (Waring et al. 2006); and about 11,200 (CV=29%) in the eastern tropical Pacific (Wade and Gerrodette 1993). Using corrections for missed animals, Ferguson and Barlow (2001) re-estimated the abundance as approximately 150,000 of both species in the eastern tropical Pacific. There is evidence of site fidelity for individuals off the island of Hawaii (Baird et al. 2006), suggesting that within-basin population structure may exist.

And:

Although never hunted commercially, these mammals were sometimes harpooned by 19th-century whalers. Dwarf sperm whales were taken in a small harpoon fishery for pilot whales at St. Vincent in the Lesser Antilles, in Japan, and occasionally in an aboriginal fishery on Lamalera Island in Indonesia, and have also been reported from fish markets in Sri Lanka (Caldwell and Caldwell, 1989). This species is also taken occasionally by harpoon off Taiwan (J. Wang pers. comm.).

A few Dwarf sperm whales are known to have died incidentally in fisheries throughout their range. When taken in commercial fisheries the numbers are so few that it is considered a rare bycatch. Zerbini and Kotas (1998) reported some bycatch in the Brazilian driftnet fishery.

Both Kogia species have been reported with plastic bags in their stomachs that may have prevented digestion of food and ultimately brought death. Perhaps the textural or visual quality of the plastic was similar to that of squid and thus enticed the whales to devour it. (Caldwell and Caldwell 1989)

In general, there are not known to be any serious human impacts, and subpopulations are probably relatively less affected by human activities than are those of most other cetaceans (Caldwell and Caldwell 1989).

While impacts of high levels of anthropogenic sound have been well documented only for beaked whales (Simmonds and Lopez-Jurado 1991; Frantzis 1998; Balcomb and Claridge 2001; US Dept of Commerce and US Navy 2001; Jepson et al. 2003; Fernandez et al. 2005), there are examples for a number of other species of odontocetes of potential impacts. While conclusive evidence of cause and effect are often lacking, strong avoidance reactions, embayments or mass stranding events have been spatially and temporally associated with high levels of anthropogenic sound for Short-finned pilot whales (Hohn et al. 2006), Melon-headed whales (Southall et al. 2006), Atlantic spotted dolphin (Balcomb and Claridge 2001), Dwarf sperm whales (Hohn et al. 2006), and Dall’s porpoise (Balcomb pers. comm.). It should be recognized that high levels of anthropogenic sound have the potential to impact all deep diving odontocete species.

In 2005, a large series of unusual stranding events over about three weeks in and around Taiwan included at least 13 Dwarf sperm whales, many of which were live strandings (Wang and Yang 2006; Yang et al. 2008). It is unknown if high-intensity anthropogenic sounds resulted in these strandings. However, “bubble-like lesions” were reported in some individuals by Yang et al. (2008). There are high levels of unexplained strandings in the Gulf of Mexico and the Atlantic coast of Florida that warrant concern (Waring et al. 2006).

Predicted impacts of global climate change on the marine environment may affect Dwarf sperm whales, although the nature of impacts is unclear (Learmonth et al. 2006)

Further Reading

  1. Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L. 2008. Kogia sima. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. Downloaded on 06 April 2011.
  2. Aguiar-Dos Santos, R. and Haimovici, M. 2001. Cephalopods in the diet of marine mammals stranded or incidentally caught along southeastern and southern Brazil (21- 34º S). Fisheries Research 52: 99-112.
  3. Banks, R. C., R. W. McDiarmid, A. L. Gardner, and W. C. Starnes. 2003. Checklist of Vertebrates of the United States, the U.S. Territories, and Canada
  4. Banks, R. C., R. W. McDiarmid, and A. L. Gardner. 1987. Checklist of Vertebrates of the United States, the U.S. Territories, and Canada. Resource Publication, no. 166. 79
  5. Baird, R. W., Schorr, G. S., Webster, D. L., Mcsweeney, D. J. and Mahaffy, S. D. 2006. Studies of beaked whale diving behavior and odontocete stock structure in Hawai'i in March/April 2006.
  6. Balcomb, K. C. and Claridge, D. E. 2001. A mass stranding of cetaceans caused by naval sonar in the Bahamas. Bahamas Journal of Science 8(2): 2-12.
  7. Barlow, J. 1999. Trackline detection probability for long-diving whales. In: G. W. Garner, S. C. Amstrup, J. L. Laake, B. J. F. Manley, L. L. McDonald and D. G. Robertson (eds), Marine mammal survey and assessment methods, pp. 209-221. Balkema Press, Netherlands.
  8. Barlow, J. 2006. Cetacean abundance in Hawaiian waters estimated from a summer/fall survey in 2002. Marine Mammal Science 22(2): 446-464.
  9. Caldwell, D. K. and Caldwell, M. C. 1989. Pygmy sperm whale Kogia breviceps (de Blainville, 1838): Dwarf sperm whale Kogia simus Owen, 1866. In: S. H. Ridgway and R. Harrison (eds), Handbook of marine mammals, Vol. 4: River dolphins and the larger toothed whales, pp. 234-260. Academic Press.
  10. Chivers, S. J., Leduc, A. E., Robertson, K. M., Barros, N. B. and Dizon, A. E. 2005. Genetic variation in Kogia spp., with preliminary evidence for two species of Kogia sima. Marine Mammal Science 21(4): 619-634.
  11. Felder, D.L. and D.K. Camp (eds.), Gulf of Mexico–Origins, Waters, and Biota. Biodiversity. Texas A&M Press, College Station, Texas.
  12. Ferguson, M. C. and Barlow, J. 2001. Spatial distribution and density of cetaceans in the eastern Pacific Ocean based on summer/fall research vessel surveys in 1986-96. Southwest Fisheries Science Center Adminstrative Report LJ-01-04: 61 pp.
  13. Fernández, A., Edwards, J. F., Rodriguez, F., Espinosa, A., De Los Monteros, Herraez, P., Castro, P., Jaber, J. R., Martin, V. and Arebelo, M. 2005. "Gas and fat embolic syndrome" involving a mass stranding of beaked whales (family Ziphiidae) exposed to anthropogenic sonar signals. Veterinary Pathology 42: 446-457.
  14. Gordon, D. (Ed.) (2009). New Zealand Inventory of Biodiversity. Volume One: Kingdom Animalia. 584 pp
  15. Hohn, A. A., Rotstein, D. S., Harms, C. A. and Southall, B. L. 2006. Multispecies mass stranding of Pilot whales (Globicephala macrorhynchus), Minke whale (Balaenoptera acutorostrata), and Dwarf sperm whales (Kogia sima) in North Carolina on 15-16 January 2005. NOAA Technical Memorandum NMFS SEFSC 537: 222.
  16. IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
  17. Jepson, P. D., Arebelo, M., Deaville, R., Patterson, I. A. P., Castro, P., Baker, J. R., Degollada, E., Ross, H. M., Herraez, P., Pocknell, A. M., Rodriguez, F., Howie, F. E., Espinosa, A., Reid, R. J., Jaber, J. R., Martin, V., Cunningham, A. A. and Fernandez, A. 2003. Gas-bubble lesions in stranded cetaceans. Nature 425: 575-576.
  18. Learmonth, J. A., Macleod, C. D., Santos, M. B., Pierce, G. J., Crick, H. Q. P. and Robinson, R. A. 2006. Potential effects of climate change on marine mammals. Oceanography and Marine Biology: An Annual Review 44: 431-464.
  19. Mcalpine, D. F. 2002. Pygmy and Dwarf sperm whales Kogia breviceps and K. simus. In: W. F. Perrin, B. Wursig and J. G. M. Thewissen (eds), Encyclopedia of Marine Mammals, pp. 1007-1009. Academic Press.
  20. Mead, James G., and Robert L. Brownell, Jr. / Wilson, Don E., and DeeAnn M. Reeder, eds. 2005. Order Cetacea. Mammal Species of the World: A Taxonomic and Geographic Reference, 3rd ed., vol. 1. 723-743
  21. Mullin, K. D. and Fulling, G. L. 2004. Abundance of cetaceans in the oceanic northern Gulf of Mexico, 1996-2001. Marine Mammal Science 20(4): 787-807.
  22. Nagorsen, D. 1985. Mammalian Species No 239. Kogia simus. American Society of Mammalogists.
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  24. Nowak, R.M. 1991. Walker's Mammals of the world, Fifth edition. John Hopkins University Press, Boston.
  25. Owen, R., 1866. On some Indian cetacea collected by Walter Elliot, Esq. Trans. Zool. Soc., 6:30. London, 6:17-47.
  26. Perrin, W. (2010). Kogia sima (Owen, 1866). In: Perrin, W.F. World Cetacea Database. Accessed through: Perrin, W.F. World Cetacea Database at http://www.marinespecies.org/cetacea/aphia.php?p=taxdetails&id=159025 on 2011-03-18
  27. Rice, Dale W. 1998. Marine Mammals of the World: Systematics and Distribution. Special Publications of the Society for Marine Mammals, no. 4. ix + 231
  28. 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) 11(14): 259-327.
  29. Simmonds, M. P. and Lopez-Jurado, L. F. 1991. Whales and the military. Nature 351: 448.
  30. Southall, B. L., Braun, R., Gulland, F. M. D., Heard, A. D., Baird, R. W., Wilkin, S. and Rowles, T. K. 2006. Hawaiian melon-headed whale (Peponocephala electra) mass stranding event of July 3-4, 2004. NOAA Technical Memorandum NMFS-OPR 31: 73 pp.
  31. Southwest Fisheries Science Center, Dwarf and Pygmy Sperm Whale, NOAA
  32. Taylor, B. L., Chivers, S. J., Larese, J. and Perrin, W. F. 2007. Generation length and percent mature estimates for IUCN assessments of Cetaceans. Southwest Fisheries Science Center.
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  36. Wang, J. Y. and Yang, S. C. 2006. Unusual cetacean stranding events of Taiwan in 2004 and 2005. Journal of Cetacean Research and Management 8: 283-292.
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Glossary

Citation

Life, E. (2011). Dwarf sperm whale. Retrieved from http://www.eoearth.org/view/article/165109

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