Indian Ocean humpback dolphin
{{Short description|Species of mammal}}
{{Speciesbox
| name = Indian Ocean humpback dolphin{{MSW3 Cetacea|id=14300082|page=732}}
| image = Dolphin-Musandam 2.jpg
| image_upright = 1.1
| image_caption = Indian Ocean humpback dolphin（S. plumbea） off Khasab in Musandam
| status = EN
| status_system = IUCN3.1
| status2 = CITES_A1
| status2_system = CITES
| status2_ref = {{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=2022-01-14|website=cites.org}}
| taxon = Sousa plumbea
| authority = (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 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.{{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|bibcode=2014MMamS..30.1494J }}
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.
Distribution and habitat
= Distribution =
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.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. 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.{{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}}
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.{{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}}
Description
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}}.{{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}} They have a fatty hump on the back, which differentiates them from S. chinensis which have a more prominent dorsal fin, but no hump.
Different varieties have different coloration, although young dolphins are generally gray, with darker gray above than below.{{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}} They are generally dark gray.
Indian Ocean humpback dolphins can appear similar to conspecific Indo-Pacific bottlenose dolphins, but the bottlenose dolphins lack the hump. 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.
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Life history
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.
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.
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.{{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}} The most driving factor appears to be chemical pollution, as tissue analysis of many stranded specimens exhibit fatal concentrations of organochlorines.{{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}}{{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}}{{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}} 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.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, 2017Gulf 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, 2017Sanker 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
Gallery
File:Indian Humpback Dolphin, Kerala, IN imported from iNaturalist photo 306681934.jpg|Dorsal fin on an Indian Ocean Humpback Dolphin
File:Indian Humpback Dolphin, India imported from iNaturalist photo 45311838.jpg|Pattern observed on the dorsal fin of Indian Humpback Dolphins
File:Indian Humpback Dolphin, Kerala, IN imported from iNaturalist photo 306681293.jpg|Profile of the Indian Ocean Humpback Dolphin as visible on the surface
File:Indian Humpback Dolphin, Dhofar, OM imported from iNaturalist photo 473647665.jpg|Blowhole of an Indian Ocean Humpback Dolphin visible on the surface
File:Indian Humpback Dolphin, Dhofar, OM imported from iNaturalist photo 473647604.jpg|Beak of an Indian Ocean Humpback Dolphin visible above the surface
File:Indian Humpback Dolphin, Abu Dhabi, AE imported from iNaturalist photo 471591756.jpg|A Pod of Indian Ocean Humpback Dolphins
File:Indian Humpback Dolphin, Maharashtra, IN imported from iNaturalist photo 60110813.jpg|Indian Ocean Humpback Dolphin lunging out of water
File:Indian Humpback Dolphin, Kerala, IN imported from iNaturalist photo 352515146.jpg|Indian Ocean Humpback Dolphin surfacing
File:Indian Humpback Dolphin, Kerala, IN imported from iNaturalist photo 455250041.jpg|Tail-walking exhibited by Indian Ocean Humpback dolphin
File:Indian Humpback Dolphin, Kerala, IN imported from iNaturalist photo 368125482.jpg|Carcass of Indian Humpback Dolphin washed ashore Kerala coast
See also
{{Portal|Cetaceans|Mammals|Marine life}}
References
{{Reflist}}
{{Cetacea}}
{{Taxonbar|from=Q20650585|from2=Q3017051}}
Category:Cetaceans of the Indian Ocean
Category:Cetaceans of the Pacific Ocean
Category:Marine fauna of Africa
Category:Marine fauna of Oceania
Category:Mammals of Southeast Asia
Category:Near threatened biota of Africa
Category:Near threatened biota of Asia