CleanupBot II at 22:00, 13 August 2023

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{{Short description|Species of mammal}}
{{Speciesbox
| name = Indian Ocean humpback dolphin<ref name=MSW3>{{MSW3 Cetacea|id=14300082|page=732}}</ref>
| image = Dolphin-Musandam 2.jpg
| image_upright = 1.1
| image_caption = Indian Ocean humpback dolphin（''S. plumbea''） off [[Khasab]] in [[Musandam Governorate|Musandam]]
| status = EN
| status_system = IUCN3.1
| status_ref = <ref name="iucn status 12 November 2021">{{cite iucn |author=Braulik, G.T. |author2=Findlay, K. |author3=Cerchio, S. |author4=Baldwin, R. |author5=Perrin, W. |date=2017 |title=''Sousa plumbea'' |volume=2017 |page=e.T82031633A82031644 |doi=10.2305/IUCN.UK.2017-3.RLTS.T82031633A82031644.en |access-date=12 November 2021}}</ref>
| status2 = CITES_A1
| status2_system = CITES
| status2_ref = <ref>{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=2022-01-14|website=cites.org}}</ref>
| taxon = Sousa plumbea
| authority = ([[Georges Cuvier|G. Cuvier]], 1829)
| range_map2 = cetacea_range_map_Indian_Humpback_Dolphin.PNG
| range_map2_caption = ''S. plumbea'' range
}}

The '''Indian Ocean humpback dolphin''' (''Sousa plumbea'') is a member of the [[Oceanic dolphin|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.<ref>{{cite journal |first1=Thomas A. |last1=Jefferson |first2=Howard C. |last2=Rosenbaum |year=2014 |title=Taxonomic revision of the humpback dolphins (''Sousa'' spp.), and description of a new species from Australia |journal=Marine Mammal Science |volume=30 |issue=4 |pages=1494–1541|doi=10.1111/mms.12152}}</ref>

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 [[Sciaenidae|sciaenid]] fishes, [[cephalopod]]s, and [[crustacean]]s.

The species is currently categorized as [[Endangered species|Endangered]].<ref name="iucn status 12 November 2021" />

==Distribution and habitat==
=== Distribution ===
''Sousa plumbea'' ranges from Southern Africa to Western Indochina, including coastal areas along East Africa, the Middle East and India. 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 [[Oman|Sultanate of Oman]] and the [[United Arab Emirates]].<ref name=":2">{{Cite journal|last1=Baldwin|first1=Robert M.|last2=Collins|first2=Moth|last3=Waerebeek|first3=Koen Van|last4=Minton|first4=Gianna|title=The Indo-Pacific Humpback Dolphin of the Arabian Region: A Status Review|journal=Aquatic Mammals|volume=30|issue=1|pages=111–124|doi=10.1578/am.30.1.2004.111|year=2004}}</ref>

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.<ref name=":0">{{Cite journal|last1=Jefferson|first1=Thomas A.|last2=Karczmarski|first2=Leszek|date=2001-01-01|title=Sousa chinensis|journal=Mammalian Species|volume=655|pages=1–9|doi=10.1644/1545-1410(2001)655<0001:sc>2.0.co;2|s2cid=198968876 |issn=0076-3519}}</ref>

=== Habitat ===
Studies have determined that the most limiting factor to habitat-usage is water depth, with a majority of specimens typically remaining in shallow waters not exceeding 20 meters in depth. As a result, the Indian Ocean humpback dolphin's offshore range is largely dependent on the coastlines' specific physiographical characteristics.<ref name=":3">{{Cite journal|last1=Parra|first1=Guido J.|last2=Corkeron|first2=Peter J.|last3=Marsh|first3=Helene|title=The Indo-Pacific Humpback Dolphin, ''Sousa chinensis'' (Osbeck, 1765), in Australian Waters: A Summary of Current Knowledge|journal=Aquatic Mammals|volume=30|issue=1|pages=197–206|doi=10.1578/am.30.1.2004.197|year=2004}}</ref><ref>{{Cite journal|last1=Karczmarski|first1=Leszek|last2=Cockcroft|first2=Victor G.|last3=Mclachlan|first3=Anton|date=2000|title=Habitat Use and Preferences of Indo-Pacific Humpback Dolphins Sousa Chinensis in Algoa Bay, South Africa|journal=Marine Mammal Science|volume=16|pages=65–79|doi=10.1111/j.1748-7692.2000.tb00904.x|s2cid=84485298 }}</ref><ref name=":0" />

The species has been reported to inhabit a variety of different coastal habitats, including both soft sediment (e.g. sand and sea grass) and hard sediment (e.g. rock and coral) marine habitats as well as estuarine habitats (e.g. lagoons, bays, rivers, and mangrove channels). Preference and prominence of any given habitat type is highly dependent on the geographical location of any given Indian Ocean humpbacked dolphin population.<ref name=":0" />

==Description==
[[File:Dolphin-Musandam 2.jpg|thumb|left|''S. plumbea'' off [[Khasab]] in [[Musandam Governorate|Musandam]]]]
The Indian Ocean humpback dolphin is a medium-sized dolphin that ranges in length from {{convert|2|to|2.8|m|ft}} and in weight from {{convert|150|to|200|kg|lb}}.<ref name=visual>{{cite book|title=Whales, Dolphins and Porpoises: The Visual Guide to All the World's Cetaceans|author=Carwardine, M.|pages=[https://archive.org/details/whalesdolphinspo00carw_1/page/174 174]–175|publisher=DK Publishing|year=1995|isbn=978-1564586209|url-access=registration|url=https://archive.org/details/whalesdolphinspo00carw_1}}</ref> They have a fatty hump on the back, which differentiates them from ''S. chinensis'' which have a more prominent dorsal fin, but no hump.<ref name=visual/>

Different varieties have different coloration, although young dolphins are generally gray, with darker gray above than below.<ref name=encyc>{{cite book|title=Encyclopedia of Marine Mammals|author1=Wells, R.|author2=Scott, M.|chapter=Humpback Dolphins|editor=Para, G.J.|editor2=Ross, G.J.B|pages=[https://archive.org/details/encyclopediaofma2002unse/page/576 576–581]|year=2002|publisher=Academic Press|isbn=978-0-12-551340-1|chapter-url=https://archive.org/details/encyclopediaofma2002unse/page/576}}</ref> They are generally dark gray.<ref name=encyc/>

Indian Ocean humpback dolphins can appear similar to conspecific [[Indo-Pacific bottlenose dolphin]]s, but the bottlenose dolphins lack the hump.<ref name=visual/> 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.<ref name=visual/>

{{-}}

==Life history==

===Growth rate===
The Indian Ocean humpback dolphin is a medium-sized dolphin that exhibit a two-phase growth rate model, in which calves and juveniles experience dramatic growth before reaching a modal peak and after which growth rate slows down as they near complete physical maturity. This modal peak is predicted to occur at around the tenth year, with neonatal individuals averaging 100 cm and growing to an approximate 220 cm by the age of 10. Completely mature adults grow to an average total length of approximately 250 cm.<ref name=":0" /><ref name=":1">{{Cite journal|last1=Jefferson|first1=Thomas A.|last2=Hung|first2=Samuel K.|last3=Robertson|first3=Kelly M.|last4=Archer|first4=Frederick I.|date=2012-01-01|title=Life history of the Indo-Pacific humpback dolphin in the Pearl River Estuary, southern China|journal=Marine Mammal Science|language=en|volume=28|issue=1|pages=84–104|doi=10.1111/j.1748-7692.2010.00462.x|issn=1748-7692|url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1282&context=usdeptcommercepub}}</ref>

=== Color pattern ===
Calves and juveniles less than a year old are typically unspotted and bear a grey coloration. Subadults slowly develop a "mottled" or "speckled" coating between the ages of 4 and 20, with females experiencing an earlier onset of this pattern development compared to males. After the age of 25, adults begin to slowly lose this spotted pattern and, once again, females experience an earlier onset and drastically faster rate of loss when compared to males.<ref name=":1" />

=== Reproduction ===
Females reach sexual maturity at an approximate age of 9 to 10 years, while males reach sexual maturity at an approximate age of 12 to 14 years.<ref>{{Cite journal|last=Jefferson|first=Thomas A.|date=2000|title=Population Biology of the Indo-Pacific Hump-Backed Dolphin in Hong Kong Waters|jstor=3830809|journal=Wildlife Monographs|volume=144|issue=144|pages=1–65}}</ref>

The Indian Ocean humpback dolphin exhibits a peak birthing season between the months of May and June, although they are capable of reproducing year round. This peak season, however, confers survival advantages to neonatal calves as it correlates with rising air and water temperatures during the later spring and early summer months.<ref name=":0" /> Gestation lasts between 10 and 12 months. Observational studies have found that most females birth a single calf at any given reproductive period, after which they undergo a calving interval that averages approximately 62 months. This prolonged calving interval is in part due to a prolonged rearing period, in which calves are nursed by their mothers for a period of up to 24 months and mother-calf associations can last between 3 and 4 years.<ref name=":0" /><ref name=":1" />

Despite this long rearing period, Indian Ocean humpback dolphins experience extremely high rates of infant mortality. Studies suggest that this heightened mortality is due to anthropogenic disturbances such as chemical pollution, habitat loss, fishing, and noise pollution.<ref name=":1" /><ref name=":2" /><ref name=":4">{{Cite journal|last1=Parsons|first1=E.C.M|last2=Chan|first2=L.|date=1998|title=Organochlorines in Indo-Pacific hump-backed dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocaenoides) from Hong Kong.|url=https://www.researchgate.net/publication/260038103|journal=The Marine Biology of the South China Sea|volume=3|pages=423–437|via=ResearchGate}}</ref><ref name=":5">{{Cite journal|last1=Jefferson|first1=Thomas A.|last2=Hung|first2=Samuel K.|last3=Lam|first3=Paul K.S.|date=2006|title=Strandings, mortality and morbidity of Indo-Pacific humpback dolphins in Hong Kong, with emphasis on the role of organochlorine contaminants.|url=https://swfsc.noaa.gov/uploadedFiles/Divisions/PRD/Publications/Jeffersonetal.06b(94).pdf|journal=Journal of Cetacean Research and Management|volume=8|pages=181–193}}</ref>

== Sociality ==
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.<ref name=":2" />

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]].<ref name=visual/><ref name=encyc/>

== Feeding ==
Very little is known on the specific species that compose the Indian Ocean humpback dolphin's diet, although multiple studies have confirmed that a majority of their diet is composed of [[Sciaenidae|sciaenid]] fishes, [[cephalopod]]s, and [[crustacean]]s.<ref name=":2" /><ref name=":3" />

A few studies have confirmed that Indian Ocean humpback dolphins perform a highly skilled and communal feeding behavior known as strand feeding, in which individuals collectively work together to herd fish onto exposed sand banks, after which they deliberately beach themselves to capture the beached fish.<ref name=":2" /><ref>{{Cite book|title=Whales and dolphins of the United Arab Emirates|last=M.|first=Baldwin, Robert|date=1995|publisher=Published by Robert M. Baldwin|isbn=978-0952660507|location=Bowlish, Somerset, England|oclc=43080658}}</ref>

==Conservation==
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.<ref>{{Cite journal|last=Karczmarski|first=Leszek|date=2000-07-01|title=Conservation and management of humpback dolphins: the South African perspective|journal=Oryx|language=en|volume=34|issue=3|pages=207–216|doi=10.1046/j.1365-3008.2000.00120.x|issn=1365-3008|doi-access=free}}</ref><ref name=":0"/> The most driving factor appears to be chemical pollution, as tissue analysis of many stranded specimens exhibit fatal concentrations of organochlorines.<ref name=":4" /><ref name=":5" /><ref>{{Cite journal|last=Parsons|first=E.C.M.|title=The Potential Impacts of Pollution on Humpback Dolphins, with a Case Study on the Hong Kong Population|journal=Aquatic Mammals|volume=30|issue=1|pages=18–37|doi=10.1578/am.30.1.2004.18|year=2004}}</ref> 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.<ref>WAM.
2017. [http://www.emirates247.com/news/emirates/abu-dhabi-has-world-s-largest-population-of-humpback-dolphins-2017-09-17-1.659122 Abu Dhabi has world’s largest population of humpback dolphins]. [[Emirates 24/7]]. Retrieved on September 21, 2017</ref><ref>[[Gulf News]]. 2017. [http://gulfnews.com/news/uae/environment/abu-dhabi-proves-a-haven-for-humpback-dolphins-1.2091551 Abu Dhabi proves a haven for humpback dolphins]. Retrieved on September 21, 2017</ref><ref>Sanker A..
2017. [https://www.khaleejtimes.com/nation/abu-dhabi/abu-dhabi-leads-world-in-humpback-dolphin-numbers- Abu Dhabi leads world in humpback dolphin numbers]. [[Khaleej Times]]. Retrieved on September 21, 2017</ref>

==See also==

*[[List of cetaceans]]

==References==
{{Reflist}}

{{Cetacea}}

{{Taxonbar|from=Q20650585|from2=Q3017051}}

{{DEFAULTSORT:dolphin, humpback, Indian Ocean}}
[[Category:Humpback dolphins|Indian Ocean humpback dolphin]]
[[Category:Cetaceans of the Indian Ocean]]
[[Category:Cetaceans of the Pacific Ocean]]
[[Category:Fauna of the Red Sea]]
[[Category:Marine fauna of Africa]]
[[Category:Marine fauna of Asia]]
[[Category:Marine fauna of Oceania]]
[[Category:Mammals of Southeast Asia]]
[[Category:National symbols of India]]
[[Category:Fauna of East Africa]]
[[Category:Near threatened biota of Africa]]
[[Category:Near threatened biota of Asia]]
[[Category:Near threatened biota of Oceania]]
[[Category:Mammals described in 1829|Indian Ocean humpback dolphin]]
[[Category:Taxa named by Georges Cuvier]]

Indian Ocean humpback dolphin - Revision history

CleanupBot II at 22:00, 13 August 2023