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Indian Ocean humpback dolphin

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Indian Ocean humpback dolphin[1]
Indian Ocean humpback dolphin（S. plumbea） off Khasab in Musandam
CITES Appendix I (CITES)[3]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Delphinidae
Genus: Sousa
Species:
S. plumbea
Binomial name
Sousa plumbea
(G. Cuvier, 1829)
S. plumbea range

The Indian Ocean humpback dolphin (Sousa plumbea) is a member of the Delphinidae family occupying coastal areas ranging from Southern Africa to Western Indochina. The Indo-Pacific humpback dolphin (Sousa chinensis) was formerly included within the same species, but a 2014 study revealed them to be a separate species.[4]

The most limiting factor to habitat-usage is water depth, with most specimens remaining in waters shallower than 20 meters. As a result, the Indian Ocean humpback dolphin's offshore range is largely dependent on the coastlines' specific physiographical characteristics. The species has been reported to inhabit nearly every type of coastal habitat, although preference and prominence of any given habitat type is highly dependent on the geographical location. Indian Ocean humpback dolphins experience extremely high rates of calf and juvenile mortality due to anthropogenic disturbances such as environmental pollution, habitat deterioration and noise pollution.

Indian Ocean humpback dolphins are social delphinids that live in groups averaging twelve individuals, although group size can be highly variable. The majority of their diet is composed of sciaenid fishes, cephalopods, and crustaceans.

The species is currently categorized as Endangered.[2]

Distribution and habitat

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Distribution

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Sousa plumbea ranges from Southern Africa to Western Indochina, including coastal areas along East Africa, the Middle East and India. There is studied population in Menai Bay Conservation Area of Tanzania's Zanzibar Archipelago.[5] Critically important populations have been determined in Southeast Asia, particularly along the southern coastlines of China. Recent investigations have, however, similarly determined critical populations along the coasts of the Arabian peninsula, particularly including the Sultanate of Oman and the United Arab Emirates.[6]

While S. plumbea and S. chinensis are genetically distinguishable, delphinids' high capacity for hybridization have resulted in hybrid populations in areas of overlapping distribution. In fact, genetic analysis has indicated that S. chinensis sampled from Indochina are more closely related to S. plumbea than to S. chinensis from Australia.

This species does not exhibit large migratory behavior.[7]

Description

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S. plumbea off Khasab in Musandam

The Indian Ocean humpback dolphin is a medium-sized dolphin that ranges in length from 2 to 2.8 metres (6.6 to 9.2 ft) and in weight from 150 to 200 kilograms (330 to 440 lb).[8] They have a fatty hump on the back, which differentiates them from S. chinensis which have a more prominent dorsal fin, but no hump.[8]

Different varieties have different coloration, although young dolphins are generally gray, with darker gray above than below.[9] They are generally dark gray.[9]

Indian Ocean humpback dolphins can appear similar to conspecific Indo-Pacific bottlenose dolphins, but the bottlenose dolphins lack the hump.[8] All humpback dolphins have a distinctive motion when surfacing, in that it surfaces at a 30- to 45-degree angle with the rostrum, and sometimes the full head, showing before arching its back and sometimes showing its flukes.[8]

Life history

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Sociality

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The Indian Ocean humpback dolphin is a social delphinid that typically lives within a group. Group size is, however, highly variable. Some specimens have been found to be isolated individuals, although the average group is composed of around 12 individuals and some of the largest observed groups have been in excess of 100 individuals.[6]

There is very little scientific evidence to support significant inter-species interactions and groupings, although rare observations have noted interactions (both friendly and aggressive) with the sympatric Indo-Pacific bottlenose dolphin, snubfin dolphin, long-snouted spinner dolphin and finless porpoise.[8][9]

Conservation

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The Indian Ocean humpback dolphin has proven to be particularly susceptible to the deleterious effects of anthropogenic activity. The species' shallow, coastal habitat heightens their exposure to anthropogenic disturbances such as habitat deterioration, mortality due to by-catch, vessel striking, and noise pollution.[10][7] The most driving factor appears to be chemical pollution, as tissue analysis of many stranded specimens exhibit fatal concentrations of organochlorines.[11][12][13] As a result, a number of nations have preemptively established conservation and management programs to ensure that the species' does not become endangered.

Recent investigative studies have revealed that the United Arab Emirates houses one of the world's largest populations.[14][15][16]

See also

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References

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  1. ^ Mead, J. G.; Brownell, R. L. Jr. (2005). "Order Cetacea". In Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. p. 732. ISBN 978-0-8018-8221-0. OCLC 62265494.
  2. ^ a b Braulik, G.T.; Findlay, K.; Cerchio, S.; Baldwin, R.; Perrin, W. (2017). "Sousa plumbea". IUCN Red List of Threatened Species. 2017: e.T82031633A82031644. doi:10.2305/IUCN.UK.2017-3.RLTS.T82031633A82031644.en. Retrieved 12 November 2021.
  3. ^ "Appendices | CITES". cites.org. Retrieved 2022-01-14.
  4. ^ Jefferson, Thomas A.; Rosenbaum, Howard C. (2014). "Taxonomic revision of the humpback dolphins (Sousa spp.), and description of a new species from Australia". Marine Mammal Science. 30 (4): 1494–1541. Bibcode:2014MMamS..30.1494J. doi:10.1111/mms.12152.
  5. ^ Temple, Andrew J., et al. "Spatial and temporal variations in the occurrence and foraging activity of coastal dolphins in Menai Bay, Zanzibar, Tanzania." PloS one 11.3 (2016): e0148995.
  6. ^ a b Baldwin, Robert M.; Collins, Moth; Waerebeek, Koen Van; Minton, Gianna (2004). "The Indo-Pacific Humpback Dolphin of the Arabian Region: A Status Review". Aquatic Mammals. 30 (1): 111–124. doi:10.1578/am.30.1.2004.111.
  7. ^ a b Jefferson, Thomas A.; Karczmarski, Leszek (2001-01-01). "Sousa chinensis". Mammalian Species. 655: 1–9. doi:10.1644/1545-1410(2001)655<0001:sc>2.0.co;2. ISSN 0076-3519. S2CID 198968876.
  8. ^ a b c d e Carwardine, M. (1995). Whales, Dolphins and Porpoises: The Visual Guide to All the World's Cetaceans. DK Publishing. pp. 174–175. ISBN 978-1564586209.
  9. ^ a b c Wells, R.; Scott, M. (2002). "Humpback Dolphins". In Para, G.J.; Ross, G.J.B (eds.). Encyclopedia of Marine Mammals. Academic Press. pp. 576–581. ISBN 978-0-12-551340-1.
  10. ^ Karczmarski, Leszek (2000-07-01). "Conservation and management of humpback dolphins: the South African perspective". Oryx. 34 (3): 207–216. doi:10.1046/j.1365-3008.2000.00120.x. ISSN 1365-3008.
  11. ^ Parsons, E.C.M; Chan, L. (1998). "Organochlorines in Indo-Pacific hump-backed dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides) from Hong Kong". The Marine Biology of the South China Sea. 3: 423–437 – via ResearchGate.
  12. ^ Jefferson, Thomas A.; Hung, Samuel K.; Lam, Paul K.S. (2006). "Strandings, mortality and morbidity of Indo-Pacific humpback dolphins in Hong Kong, with emphasis on the role of organochlorine contaminants" (PDF). Journal of Cetacean Research and Management. 8: 181–193.
  13. ^ Parsons, E.C.M. (2004). "The Potential Impacts of Pollution on Humpback Dolphins, with a Case Study on the Hong Kong Population". Aquatic Mammals. 30 (1): 18–37. doi:10.1578/am.30.1.2004.18.
  14. ^ WAM. 2017. Abu Dhabi has world’s largest population of humpback dolphins. Emirates 24/7. Retrieved on September 21, 2017
  15. ^ Gulf News. 2017. Abu Dhabi proves a haven for humpback dolphins. Retrieved on September 21, 2017
  16. ^ Sanker A.. 2017. Abu Dhabi leads world in humpback dolphin numbers. Khaleej Times. Retrieved on September 21, 2017
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