View source for South Asian river dolphin

{{Short description|Genus of freshwater dolphin}}
{{Featured article}}
{{Use dmy dates|date=June 2020}}
{{Automatic taxobox
| fossil_range = {{Fossil range|0.012|0}} [[Quaternary]] – recent<ref name=fossilworks>{{cite web|title=Platanista Wagler 1830 (toothed whale)|url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=63564|website=Paleobiology Database|access-date=26 March 2018|archive-date=12 December 2021|archive-url=https://web.archive.org/web/20211212182152/http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=63564|url-status=live}}</ref>
| image =Ganges River Dolphin cropped.jpg
| image_caption = [[Ganges river dolphin]] breaking the surface
| taxon = Platanista
| authority = [[Johann Georg Wagler|Wagler]], 1830
| type_species = ''[[Platanista gangetica|Delphinus gangeticus]]''<ref>{{MSW3|id=14300133}}</ref>
| type_species_authority = Lebeck, 1801
| subdivision_ranks = Species
| subdivision = ''[[Platanista gangetica]]''<br />
''[[Platanista minor]]''
| range_map = SouthAsianRiverDolphin_distribution2019.png
| range_map_caption = Current ranges of the <span style="color:#0202fd;">Indus river dolphin</span>  and <span style="color:#f2790e;">Ganges river dolphin</span> 
}}

'''South Asian river dolphins''' are [[toothed whale]]s in the genus '''''Platanista''''', which inhabit the waterways of the [[Indian subcontinent]]. They were historically considered to be one species (''P. gangetica'') with the [[Ganges river dolphin]] and the [[Indus river dolphin]] being subspecies (''P. g. gangetica'' and ''P. g. minor'' respectively).  Genetic and morphological evidence led to their being described as separate species in 2021. The Ganges and Indus river dolphins are estimated to have [[Split (phylogenetics)|diverged]] 550,000 years ago. They are the only living members of the family [[Platanistidae]] and the superfamily Platanistoidea. Fossils of ancient relatives date to the [[late Oligocene]]. 

South Asian river dolphins are small but stocky [[cetacean]]s with long snouts or [[Rostrum (anatomy)|rostra]], broad flippers, and small dorsal fins. They have several unusual features. Living in murky river waters, they have eyes that are tiny and lensless; the dolphins rely instead on [[Animal echolocation|echolocation]] for navigation. The skull has large crests over the [[Melon (cetacean)|melon]], which help direct their echolocation signals. These dolphins prey mainly on fish and shrimp and hunt them throughout the [[water column]]. They are active through the day and are sighted in small groups. Both species are listed as [[Endangered species|endangered]] by the [[IUCN Red List]] of mammals. Major threats include dams, [[Barrage (dam)|barrages]], fishing nets, and both chemical and [[noise pollution|acoustic]] pollution.

==Taxonomy==
South Asian river dolphins were traditionally considered to be one species, ''Platanista gangetica'', with the Ganges and Indus River populations being subspecies (''P. g. gangetica'' and ''P. g. minor'', respectively). [[Heinrich Julius Lebeck]] named the Ganges river dolphin ''Delphinus gangeticus'' in 1801, while [[Johann Georg Wagler]] coined the genus name ''Platanista'' in 1830,<ref name="Braulik_al20212">{{Cite journal|last1=Braulik|first1=G. T.|last2=Archer|first2=F. I.|last3=Khan|first3=U.|last4=Imran|first4=M.|last5=Sinha|first5=R. K.|last6=Jefferson|first6=T. A.|last7=Donovan|first7=C.|last8=Graves|first8=J. A.|year=2021|title=Taxonomic revision of the South Asian River dolphins (''Platanista''): Indus and Ganges river dolphins are separate species|journal=Marine Mammal Science|volume=37|issue=3|pages=1022–1059|doi=10.1111/mms.12801|doi-access=free|bibcode=2021MMamS..37.1022B |hdl=10023/21691|hdl-access=free}}</ref> a [[Latin]] word derived from the [[Ancient Greek|Greek]] "platanistēs", which may be related to the Greek words platē ("oar") or platē ("flat, broad").<ref>{{cite web|title=''Platanista''|website=Merriam-Webster.com Dictionary|url=https://www.merriam-webster.com/dictionary/Platanista|access-date=22 September 2022|archive-date=22 September 2022|archive-url=https://web.archive.org/web/20220922190833/https://www.merriam-webster.com/dictionary/Platanista|url-status=live}}</ref> This name was first given to the Ganges dolphin by [[Pliny the Elder]] in ''[[Naturalis Historia]]'' back in 77 [[Common Era|CE]]. In 1853, [[Richard Owen]] described a specimen from the Indus and considered it to be the same species as the Ganges river dolphin, but a smaller form.<ref name="Braulik_al20212"/>

Based on differences in skull and vertebrae structure, blood proteins, and [[lipid]]s, scientists declared them to be separate species in the 1970s.<ref name=Pilleri>{{cite journal |author=Pilleri, G. |author2=Marcuzzi, G. |author3=Pilleri, O. |year=1982 |title=Speciation in the Platanistoidea, systematic, zoogeographical and ecological observations on recent species |journal=Investigations on Cetacea |volume=14 |pages=15–46}}</ref><ref name="Braulik_al2014"/> The results of these studies were criticized for their small sample sizes and the absence of statistical analyses; by the late 1990s, the two populations were again considered to be two subspecies of a single species.<ref>{{cite book|author=Rice, D.|year=1998|title=Marine Mammals of the World: Systematics and Distribution|publisher=Society for Marine Mammalogy|page=92|isbn=978-1-891276-03-3}}</ref><ref name="Braulik_al2014"/> A 2014 [[mitochondrial DNA]] study found insufficient differences to support their classification as separate species.<ref name="Braulik_al2014">{{Cite journal|year=2014 |title=One Species or Two? Vicariance, lineage divergence and low mtDNA diversity in geographically isolated populations of South Asian River Dolphin |journal=Journal of Mammalian Evolution |volume=22 |issue=1 |pages=111–120 |doi=10.1007/s10914-014-9265-6 |last1=Braulik |first1=G. T. |last2=Barnett |first2=R. |last3=Odon|first3=V.|last4=Islas-Villanueva|first4=V.|last5=Hoelzel|first5=A. R. |last6=Graves|first6=J. A. |s2cid=14113756 |url=https://www.researchgate.net/publication/262524058}}</ref> However, a 2021 study reanalyzed the two populations and found significant genetic divergence and major differences in skull structure; this led to the conclusion that the two were indeed distinct species.<ref name="Braulik_al20212"/>

===Evolution===
South Asian river dolphins are the only surviving members of the family [[Platanistidae]] and the superfamily Platanistoidea.<ref name=Viglino/> They are not [[Monophyly|closely related]] to [[river dolphin]]s of the families [[Lipotidae]], [[Pontoporiidae]], and [[Iniidae]], which all [[convergent evolution|independently adapted]] to freshwater habitats.<ref name=Hamilton/> The following [[cladogram]] is based on Gatesy and colleagues (2012) and McGowen and colleagues (2020), and shows the relationship of South Asian river dolphins to other living toothed whale families:<ref>{{cite journal|author1=Gatesy, John|author2=Geisler, Jonathan H.|author3=Chang, Joseph|author4=Buell, Carl|author5=Berta, Annalisa|author6=Meredith, Robert W.|author7=Springer, Mark S.|author8=McGowen, Michael R.|url=https://www.montclair.edu/profilepages/media/5008/user/Gatesy_et_al._2012_A_phylogenetic_blueprint_for_a_modern_whale.pdf|title=A phylogenetic blueprint for a modern whale|journal=Molecular Phylogenetics and Evolution|year=2012|access-date=4 September 2015|volume=66|issue=2|pages=479–506|doi=10.1016/j.ympev.2012.10.012|pmid=23103570|archive-date=9 June 2015|archive-url=https://web.archive.org/web/20150609233831/https://www.montclair.edu/profilepages/media/5008/user/Gatesy_et_al._2012_A_phylogenetic_blueprint_for_a_modern_whale.pdf|url-status=live}}</ref><ref>{{cite journal|last1=McGowen|first1=M. R.|last2=Tsagkogeorga|first2=G.|last3=Álvarez-Carretero|first3=S.|display-authors=etal|year=2020|title=Phylogenomic resolution of the cetacean tree of life using target sequence capture|journal=Systematic Biology|volume=69|issue=3|pages=479–501|doi=10.1093/sysbio/syz068|pmid=31633766 |pmc=7164366 }}</ref>

{{Clade|style=font-size:85%;line-height:100%;width:580px;
                     |label1='''[[Toothed whales]]'''
                     |1={{Clade
                        |1={{Clade
                              |1=[[Sperm whale]]s (Physeteridae) [[File:Physeter macrocephalus NOAA.jpg|50 px]]
                              |2=[[Dwarf sperm whale]]s (Kogiidae) [[File:Kogia sima (transparent background).png|50 px]]
                              }}
                           |2={{Clade
                              |1='''South Asian river dolphins''' (Platanistidae) [[File:Ganges.png|50 px]]
                              |2={{Clade
                                 |1=[[Beaked whale]]s (Ziphiidae) [[File:Ziphius cavirostris NOAA.jpg|50 px]]
                                 |2={{Clade
                                    |label1=South American river dolphins
                                    |1={{Clade
                                       |1=[[Pontoporiidae]] [[File:Pontoporia blainvillei.jpg|50 px]]
                                       |2=[[Iniidae]] <span style="{{MirrorH}}">[[File:Inia geoffrensis.jpg|50 px]]</span>
                                       }}
                                    |label2=[[Delphinoidea]]
                                    |2={{Clade
                                       |1=[[Oceanic dolphins]] (Delphinidae) [[File:Orcinus orca NOAA 2.jpg|50 px]]
                                       |2={{Clade
                                          |1=[[Porpoise]]s (Phocoenidae) [[File:Vaquita swimming through the void. (Phocoena Sinus).png|50 px]]
                                          |2=[[beluga whale|Belugas]], [[narwhal]]s ([[Monodontidae]]) [[File:Delphinapterus leucas NOAA.jpg|50 px]]
}} }} }} }} }} }} }}

Several fossil species have been classified under Platanistoidea, the earliest of which date back to the [[late Oligocene]] ({{circa|25}} million years ago). The number of species peaked around the [[early Miocene]] ({{circa|19}} million years ago) and declined afterward. Examples of ancient platanistids include the genera ''[[Otekaikea]]'' and ''[[Waipatia]]'' and the species ''[[Awamokoa tokarahi]]'' of late Oligocene New Zealand, the family [[Allodelphinidae]] of early Miocene North Pacific, and ''[[Notocetus vanbenedeni]]'' and ''[[Aondelphis talen]]'' of early Miocene Patagonia. Platanistidae fossils have been found in Miocene deposits in Europe and North America. Fossil Platanistoidea showed a diversity of [[cochlea]] shapes, though ''Platanista'' was unusual in that it developed flatter spirals with larger gaps between them.<ref name=Viglino>{{cite journal|last1=Viglino|first1=M.|last2=Gaetán|first2=M.|last3=Buono|first3=M. R.|last4=Fordyce|first4=R. E.|last5=Park|first5=T.|year=2021|title=Hearing from the ocean and into the river: the evolution of the inner ear of Platanistoidea (Cetacea: Odontoceti)|journal=Paleobiology|volume=47|issue=4|pages=591–611|doi=10.1017/pab.2021.11|bibcode=2021Pbio...47..591V|s2cid=233517623|url=https://zenodo.org/record/4480277|access-date=31 October 2022|archive-date=5 April 2023|archive-url=https://web.archive.org/web/20230405215841/https://zenodo.org/record/4480277|url-status=live}}</ref> 

During the middle Miocene, the ancestor of ''Platanista'' entered the [[Indo-Gangetic Plain]], then covered by [[inland seas]], and remained there when sea levels dropped in the late [[Neogene]] and its environment converted to freshwater.<ref name=Hamilton>{{cite journal|last1=Hamilton|first1=H.|last2=Caballero|first2=S.|last3=Collins|first3=A. G.|last4=Brownell |first4=R. L. Jr.|year=2001|title=Evolution of river dolphins|journal=Proceedings: Biological Sciences|volume=268|issue=1466|pages=549–556|doi=10.1098/rspb.2000.1385|jstor=3068225|pmid=11296868|pmc=1088639}}</ref> River dolphins likely traveled from the [[Ganges River]] basin to the [[Indus River|Indus]] via [[stream capture]] within the last five million years. The [[Split (phylogenetics)|split]] between the two species is estimated to have occurred around 550,000 years ago based on mitochondrial DNA.<ref>{{cite journal|last1=Braulik|first1=G.|last2=Barnett|first2=R.|last3=Odon|first3=V.|last4=Islas-Villanueva|first4=V.|last5=Hoelzel|first5=R.|last6=Graves|first6=J. A.|year=2015|title=One species or two? Vicariance, lineage divergence and low mtDNA diversity in geographically isolated populations of South Asian river dolphin|journal=Journal of Mammalian Evolution|volume=22|issue=1|pages=111–120|doi=10.1007/s10914-014-9265-6|s2cid=14113756}}</ref>

==Description==
{{multiple image|align=right|direction=vertical
|image1=A-Platanista-gangetica-showing-the-body-shape-and-especially-the-head-with-a-long-beak.png|alt1=Dead dolphin lying on grass
|image2=Indus River dolphin skull cast.jpg|alt2=Dolphin skull with white background
|caption2=Full body (top) and skull of Indus river dolphin}}
South Asian river dolphins are stocky with broad, squared-off [[pectoral fin]]s; elongated, slender [[Rostrum (anatomy)|rostrum]]s (snouts); and tiny triangular [[dorsal fin]]s. Their neck joints give them great flexibility.<ref name="Braulik_al20212"/><ref name="Cassens2000">{{cite journal|last1=Cassens|first1=I.|last2=Vicario|first2=S.|last3=Waddell|first3=V. G.|last4=Milinkovitch|first4=M. C.|display-authors=etal|year=2000|title=Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages|journal=PNAS|volume=97|issue=21|pages=11343–11347|doi=10.1073/pnas.97.21.11343|pmid=11027333|pmc=17202|bibcode=2000PNAS...9711343C |doi-access=free}}</ref><ref name=Jefferson/> Unusual among cetaceans, the [[Blowhole (anatomy)|blowhole]] is slit-shaped.<ref name=Jefferson/> The finger bones can also be seen through the flippers.<ref name="Cassens2000"/> South Asian river dolphins possess some features that are "[[Primitive (phylogenetics)|primitive]]" for a cetacean, such as a [[cecum]] connected to the gut and air sacs near the blowhole. The testes of the males are located closer to the underside than in marine dolphins and descend more.<ref name=supplemantary/> Their skin ranges from grey to greyish-brown in colour, though the rostrum and surrounding areas may have some pinkish colouration. The Indus species tends to be more brownish.<ref name="Braulik_al20212"/>

In one study sampling 46 Ganges river dolphins, the maximum length and weight recorded were  {{convert|267|cm|ft|abbr=on}} and {{convert|108|kg|abbr=on}}. For the Indus species, the maximum length and weight were {{convert|241|cm|ft|abbr=on}} and {{convert|120|kg|abbr=on}} (80 individuals sampled).  Female Ganges dolphins are generally longer than Indus dolphins of both sexes, while male Ganges dolphins are shorter than Indus dolphins of both sexes. Indus dolphins tend to be proportionally heavier than Ganges dolphins, independent of sex.<ref name="Braulik_al20212"/>

South Asian river dolphin skulls have unusual features. The [[maxilla]] (fixed upper jawbone) has [[Skeletal pneumaticity|pneumatic]] extensions or "crests" on each side which curve around the [[Melon (cetacean)|melon]] and protrude forward over the rostrum. These likely help them focus their echolocation signals in their riverine environment.<ref name="Jensen">{{cite journal|last1=Jensen|first1=F. H.|last2=Rocco|first2=A.|last3=Mansur|first3=R. M.|last4=Smith|first4=B. D.|last5=Janik|first5=V. M.|last6=Madsen|first6=P. T.|year=2013|title=Clicking in shallow rivers: short-range echolocation of Irrawaddy and Ganges river dolphins in a shallow, acoustically complex habitat|journal=PLOS ONE|volume=8|issue=4|article-number=e59284|doi=10.1371/journal.pone.0059284|pmid=23573197 |pmc=3616034 |bibcode=2013PLoSO...859284J |doi-access=free }}</ref> The Ganges species also has a protrusion near the [[frontal suture]], which distinguishes it from the Indus species.<ref name="Braulik_al20212"/> The teeth of South Asian river dolphins are curved and longer in the front, where they remain exposed when the jaws are closed.<ref name=Jefferson>{{cite book|last1=Jefferson|first1=Thomas A.|last2=Webber|first2=Marc A.|last3=Pitman|first3=Robert L.|year=2015|title=Marine Mammals of the World: A Comprehensive Guide to Their Identification|publisher=Academic Press|edition=2nd|pages=346–349|isbn=978-0-12-409542-7}}</ref> Indus dolphins have more teeth than Ganges dolphins, averaging 33.2 teeth in the upper jaw and the 32.9 in the lower jaw, as compared to 28.4 in the upper jaw and 29.4 in the lower.<ref name="Braulik_al20212"/> 

Living in murky waters, South Asian river dolphins are nearly blind, their tiny eyes having flattened [[cornea]]s and no [[Lens (anatomy)|lens]]. The [[retina]]—which connects to a reduced [[optic nerve]]—does not form images but instead merely discerns light. The animal relies on a [[sphincter]]-like muscle around the eye to control access to the retina and prevent [[light scattering]], similar to a [[Pinhole (optics)|pinhole]].<ref name=":0">{{Cite journal|last1=Herald|first1=Earl S.|last2=Brownell|first2=Robert L.|last3=Frye|first3=Fredric L.|last4=Morris|first4=Elkan J.|last5=Evans|first5=William E.|last6=Scott|first6=Alan B.|year=1969|title=Blind river dolphin: first side-swimming cetacean|journal=Science|volume=166|issue=3911|pages=1408–1410|jstor=1727285|doi=10.1126/science.166.3911.1408|pmid=5350341|bibcode=1969Sci...166.1408H|s2cid=5670792|url=https://digitalcommons.unl.edu/usdeptcommercepub/138|access-date=1 December 2019|archive-date=2 August 2023|archive-url=https://web.archive.org/web/20230802073543/https://digitalcommons.unl.edu/usdeptcommercepub/138/|url-status=live|url-access=subscription}}</ref> The ears are adapted to hearing low frequencies, having a short, flattened cochlea with widely spaced spirals.<ref name=Viglino/>

==Distribution and habitat==
[[File:South_Asian_river_dolphin©_Md_Sharif_Hossain_Sourav.jpg|thumb|Ganges river dolphin in the [[Sundarbans]], Bangladesh|alt=Dolphin back and fin breaking water surface]]

South Asian river dolphins inhabit the northern waterways of the [[Indian subcontinent]]. Ganges river dolphins live in the Ganges, [[Brahmaputra River|Brahmaputra]], [[Meghna River|Meghna]], [[Karnaphuli]], and [[Sangu River|Sangu]] rivers and their [[tributaries]]. Their range extends from the [[Himalayas|Himalayan]] foothills to the [[Ganges Delta]], across the countries of [[Nepal]], [[India]] and [[Bangladesh]].<ref name="Braulik_al20212"/><ref name=Jefferson/> It is unknown if they are present in [[Bhutan]].<ref name="iucn status 2022"/> Outflows of freshwater into the [[Bay of Bengal]] have allowed them to swim along the coast, and there is at least one record of an individual entering the [[Budhabalanga River]], around {{convert|300|km|abbr=on}} southwest of the Ganges Delta.<ref name="Sinha2014"/> This species has maintained much of its range since the 19th century but has disappeared from some northern and western rivers and waterways.<ref name="Braulik_al20212"/> 

The Indus river dolphin mainly lives in the [[Indus River]] of [[Pakistan]], with three subpopulations between the [[Chashma Barrage|Chashma]], [[Taunsa Barrage|Taunsa]], [[Guddu Barrage|Guddu]], and [[Sukkur Barrage|Sukkur]] [[Barrage (dam)|barrages]]. Two other populations exist south of Sukkur and in the [[Beas River]] of India.<ref name="Braulik_al20212"/><ref name="IWC">{{cite report|last1=Aisha|first1=H.|last2=Khan|first2=U.|date=April 2021|title=Abundance survey for Indus river dolphin, Final Report|publisher=IWC Small Cetacean Fund|doi=10.13140/RG.2.2.24280.83207}}</ref> In the 19th century, this species was reported to have occurred throughout the Indus River system, from the [[Indus River Delta]] north to [[Kalabagh]] just south of the Himalayas, including all the main tributaries.<ref name="Braulik_al20212"/> The Indus river dolphin is reported to have disappeared between the [[Jinnah Barrage|Jinnah]] and Chashma barrages after 2001.<ref name="IWC"/> 

South Asian river dolphins inhabit major river channels during the [[dry season]] and travel to smaller tributaries for the [[monsoon]]. They are most commonly found in [[stream pool]]s, [[meander]]s, and [[confluence]]s, and around [[river island]]s and [[shoal]]s, which produce relatively stable waters.<ref name="Sinha2014">{{Cite journal |last1=Sinha|first1=R. K.|last2=Kannan|first2=K. |year=2014 |title=Ganges river dolphin: an overview of biology, ecology, and conservation status in India |journal=Ambio |volume=43|issue=8|pages=1029–1046 |doi=10.1007/s13280-014-0534-7 |pmc=4235892 |pmid=24924188|bibcode=2014Ambio..43.1029S }}</ref> They can be found in pools over {{convert|30|m|abbr=on}} deep, but usually dwell in shallower water.<ref name=Jefferson/>

==Behaviour and life history==
South Asian river dolphins appear to be active throughout the day. Living in flowing waters, they swim almost constantly with only brief periods of sleep, which add up to seven hours per day.<ref>{{cite journal|last=Pilleri|first=G.|year=1979|title=The blind Indus dolphin, ''Platanista indi''|journal=Endeavour|volume=3|issue=2|pages=48–56|doi=10.1016/0160-9327(79)90066-8}}</ref> They swim on their sides when in shallow water.<ref name=feeding/> River dolphins generally surface with the rostrum, head, and dorsal fin breaking the water and rarely [[Cetacean surfacing behaviour#Breaching and lunging|breach]] or raise the tail fluke, though surface activity can vary based on age, distance from shore and time of day. Diving may last as long as eight minutes among adults and subadults; dives of newborns and juveniles are not as long.<ref>{{cite journal|last1=Sinha|first1=R. K.|last2=Sinha|first2=S.|last3=Sharma|first3=G.|last4=Kedia|first4=D. K.|year=2010|title=Surfacing and diving behaviour of free-ranging Ganges river dolphin, ''Platanista gangetica gangetica''|journal=Current Science|volume=98|issue=2|pages=230–236|jstor=24111514}}</ref> 
[[File:B-Platanista-gangetica-in-natural-habitat.png|thumb|right|Indus river dolphins leaping|alt=Two dolphins leaping out of water]]
River dolphins are typically seen alone or in groups of up to 10 individuals, though enough natural resources may attract up to 30 dolphins. Individuals do not appear to have strong social bonds, outside of mothers and calves.<ref name=Jefferson/> Living in shallow river environments with acoustic obstacles, these dolphins echolocate using repetitive clicks spaced 10 to 100 [[millisecond]]s apart.<ref name="Jensen22">{{cite journal |last1=Jensen |first1=F. H. |last2=Rocco |first2=A. |last3=Mansur |first3=R. M. |last4=Smith |first4=B. D. |last5=Janik |first5=V. M. |last6=Madsen |first6=P. T. |year=2013 |title=Clicking in shallow rivers: short-range echolocation of Irrawaddy and Ganges river dolphins in a shallow, acoustically complex habitat |journal=PLOS ONE |volume=8 |issue=4 |article-number=e59284 |doi=10.1371/journal.pone.0059284 |pmc=3616034 |pmid=23573197 |bibcode=2013PLoSO...859284J |doi-access=free}}</ref><ref>{{cite book |last1=Sugimatsu |first1=H. |last2=Ura |first2=T. |last3=Mizuno |first3=K. |last4=Asada |first4=A. |title=2012 Oceans |chapter=Study of acoustic characteristics of Ganges river dolphin calf using ehcolocation clicks recorded during long-term in-situ observation |publisher=Oceans 2012 Conference |year=2012 |isbn=978-1-4673-0829-8 |pages=1–7 |doi=10.1109/OCEANS.2012.6405029 |s2cid=22758375}}</ref> Their clicks are about one [[octave]] below those of oceanic toothed whales of comparable size, meaning that they provide less information about the location of an object, but the dolphins' maxillary crests likely compensate by providing greater directional sensitivity.<ref name="Jensen"/> Vocalisations used for communication include bursts and twitterings.<ref>{{cite journal|last1=Mizue|first1=K.|last2=Masaharu|first2=N.|last3=Akira|first3=T.|year=1971|title=The underwater sounds of Ganges River dolphin (Platanista gangetica)|journal= The Scientific Reports of the Whales Research Institute|volume=23|pages=123–128}}</ref>

River dolphins feed mainly on fish and shrimp. In one [[meta study]], around 46% of prey items were found to be [[Benthic zone|bottom-dwelling]] species, while 31% were near the surface, and 23% occupied the middle of the column. The most frequently taken prey are [[Bagridae|bagrid catfish]], [[Barb (fish)|barbs]], [[Ambassidae|glass perches]], [[Mastacembelidae|spiny eels]], [[Gobiidae|gobies]], and [[Palaemonidae|prawns]]. When hunting at the surface, dolphins listen for the movements of schooling fish which are then herded with spins, side-swimming, and [[Cetacean surfacing behavior #Lobtailing and slapping|lobtailing]]. Echolocation signals are not frequently used at the surface, since many fish at this level can hear ultrasound. At the mid-surface level, the dolphins use more echolocation clicks to find prey hidden in clutter and vegetation as far as {{convert|20|m|abbr=on}} away. They flush out bottom-dwelling prey by digging around.<ref name=feeding>{{cite journal|last1=Kelhar|first1=N.|last2=Dey|first2=S.|last3=Deshpande|first3=K.|last4=Choudhary|first4=S. K.|last5=Dey|first5=S.|last6=Morisaka|first6=T.|year=2018|title=Foraging and feeding ecology of ''Platanista'': an integrative review|journal=Mammal Review|volume=48|issue=3|pages=194–208|doi=10.1111/mam.12124|bibcode=2018MamRv..48..194K |s2cid=89753459}}</ref> 

Little is known about reproduction in these river dolphins.<ref name=Jefferson/> Courtship and mating behaviour for the Ganges species has been documented from March to May, when the water level is lower, and involves multiple males chasing one female and ends with one of the males earning the right to mate.<ref name=supplemantary>{{Cite journal |last1=Sinha|first1=R. K.|last2=Kannan|first2=K. |year=2014 |title=Ganges river dolphin: an overview of biology, ecology, and conservation status in India (Supplementary material 1) |journal=Ambio |volume=43|issue=8|pages=1029–1046 |doi=10.1007/s13280-014-0534-7 |pmc=4235892 |pmid=24924188|bibcode=2014Ambio..43.1029S }}</ref> Calves are born around a year later.<ref name=Perrin2015>{{cite book|editor-first1=William F.|editor-last1=Perrin|editor-first2=Bernd |editor-last2= Wursig|editor-first3=J. G. M. |editor-last3=Thewissen|title=Encyclopedia of Marine Mammals|publisher=Academic Press|isbn= 978-0-12-804327-1|year=2015|last1=Smith|first1=B. D. |last2=Braulik|first2=G. T.|contribution=Susu and Bhulan|pages=1135–1139}}</ref> Births in the Ganges river dolphin appear to be most frequent between December and January and between March and May. For Indus river dolphins, newborns are most commonly seen between April and May.<ref name=Jefferson/> Indus river dolphins calves are around {{convert|70|cm|abbr=on}} long at birth and may nurse for up to a year. They eat their first solid food within a couple months. South Asian river dolphins reach sexual maturity at around ten years, though males may not reach their adult size until 20 years.<ref>{{cite journal|last=Kasuya|first=T.|year=1972|title=Some information on the growth of the Ganges dolphin with a comment on the Indus dolphin|journal= The Scientific Reports of the Whales Research Institute|volume=24|pages=87–108}}</ref> Growth layers in the teeth suggest South Asian river dolphins can live up to 30 years.<ref>{{cite journal|last1=Lockyer|first1=C. H.|last2=Braulik|first2=G. T.|year=2014|title=An evaluation of age estimation using teeth from South Asian River dolphins (Platanistidae)|journal=NAMMCO Scientific Publications|volume=10|doi=10.7557/3.3268|doi-access=free|hdl=10023/20641|hdl-access=free}}</ref>

==Conservation==
[[File:Ganges-river-dolphins.jpg|thumb|right|Man holding Ganges river dolphin in [[Bhagalpur]]|alt=Man standing in water while holding dolphin]]
As of 2022, the [[IUCN Red List]] of mammals lists both South Asian river dolphins as [[Endangered species|endangered]].<ref name="iucn status 2022">{{cite iucn |author1=Kelkar, N.|author2=Smith, B. D.|author3=Alom, M. Z.|author4=Dey, S.|author5=Paudel, S.|author6=Braulik, G. T.|date=2022 |title=''Platanista gangetica'' |volume=2022 |article-number=e.T41756A50383346 |doi=10.2305/IUCN.UK.2022-1.RLTS.T41756A50383346.en |access-date=17 October 2022}}</ref><ref name=IUCN>{{cite iucn |title=''Platanista minor''  |author=Braulik, G. T.|author2=Khan, U. |author3=Malik, M. |author4=Aisha, H.|year=2022 |article-number= e.T41757A50383490 |doi=10.2305/IUCN.UK.2022-1.RLTS.T41757A50383490.en|access-date=14 October 2022}}</ref> Two assessments in 2014 and 2015 estimated populations of 3,500 for the Ganges river dolphin and 1,500 for the Indus river dolphin.<ref name="Sinha2014"/><ref name="Braulik2015">{{Cite journal|year=2015|title=Review of status, threats, and conservation management options for the endangered Indus River blind dolphin|url=https://www.sciencedirect.com/science/article/abs/pii/S0006320715300999|journal=Biological Conservation|language=en|volume=192|pages=30–41|doi=10.1016/j.biocon.2015.09.008|issn=0006-3207|last1=Braulik|first1=Gill T.|last2=Noureen|first2=Uzma|last3=Arshad|first3=Masood|last4=Reeves|first4=Randall R.|bibcode=2015BCons.192...30B |access-date=27 August 2021|archive-date=22 September 2022|archive-url=https://web.archive.org/web/20220922070257/https://www.sciencedirect.com/science/article/abs/pii/S0006320715300999|url-status=live|url-access=subscription}}</ref> A survey of Indian rivers between 2021 and 2023 found over 6,000 Ganges river dolphins and only three Indus river dolphins.<ref>{{cite web|author=Mollan, Cherylann|date=5 April 2025|title=India's rivers are home to 6,000 dolphins - but they are in trouble|website=BBC.com|url=https://www.bbc.com/news/articles/cg70pprzegyo|access-date=10 April 2025}}</ref> The habitat of these river dolphins intersects with some of the most densely populated areas, leading to intense competition for water and resources.<ref name="Sinha2014"/><ref name="Braulik2015"/><ref name=Paudel2020/> 

The creation of dams and barrages in the Indus River system have heavily [[habitat fragmentation|fragmented]] the range of the Indus river dolphin, leading to a population decline of 80% since the 19th century.<ref name="Braulik2015"/> Around 50 such structures have been built in the historical range of the Ganges species.<ref name="Sinha2014"/> Fragmentation of populations makes these dolphins more vulnerable to inbreeding.<ref name=Paudel2020/> The heavy extraction of water in these dense populations also puts the dolphins at risk.<ref name="Sinha2014"/>

River dolphins [[Bioaccumulation|accumulate]] high amounts of [[persistent organic pollutant]]s, [[pesticides]], and [[heavy metals]] in their system due to being at the top of their riverine [[food web]].<ref name="Sinha2014"/><ref name="Braulik2015"/> Hence, they are seen as [[bioindicator]]s for the health of river systems.<ref name="Sinha2014"/> Fishermen compete with these animals for fish of certain sizes.<ref name=Paudel2020>{{cite journal|last1=Paudel|first1=S.|last2=Koprowski|first2=J. L.|year=2020|title=Factors affecting the persistence of endangered Ganges River dolphins (''Platanista gangetica gangetica'')|journal=Ecology and Evolution|volume=10|issue=6|pages=3138–3148|doi=10.1002/ece3.6102|pmid=32211183 |pmc=7083702 |bibcode=2020EcoEv..10.3138P }}</ref> Dolphins captured in fishing nets are usually [[Bycatch|accidental]], but dolphin oil is sought after as a fish lure, and thus fishermen may be motivated to kill caught dolphins.<ref name="Sinha2014"/> Being nearly blind and relying on echolocation for navigation, river dolphins are also negatively affected by [[noise pollution]] from boats.<ref>{{cite journal|last1=Dey|first1=M.|last2=Krishnaswamy|first2=J.|last3=Morisaka|first3=T.|last4=Kelkar|first4=N.|year=2019|title=Interacting effects of vessel noise and shallow river depth elevate metabolic stress in Ganges river dolphins|journal=Scientific Reports|volume=9|issue=15426|page=15426 |doi=10.1038/s41598-019-51664-1|pmid=31659202|pmc=6817857|bibcode=2019NatSR...915426D |s2cid=204918073}}</ref>

South Asian river dolphins are protected by law in all the states they inhabit. They can be found in numerous protected areas,<ref name="iucn status 2022"/><ref name=IUCN/> including ones established specifically for them, such as the [[Indus Dolphin Reserve]] in Pakistan and the [[Vikramshila Gangetic Dolphin Sanctuary]] in India.<ref name="Sinha2014"/><ref name="Braulik2015"/> International trade is prohibited by the listing of the South Asian river dolphins on Appendix I of the [[Convention on International Trade in Endangered Species]].<ref name="Appendices {{!}} CITES">{{Cite web|title=Appendix I|url=https://cites.org/eng/app/appendices.php|access-date=2023-01-06|date=2022-06-22|work=Convention on International Trade in Endangered Species of Wild Fauna and Flora|archive-date=5 October 2011|archive-url=https://web.archive.org/web/20111005165017/http://www.cites.org/eng/app/appendices.shtml|url-status=live}}</ref> The Ganges and Indus river dolphins are considered to be the [[List of national animals|national aquatic animals]] of India and Pakistan respectively.<ref name="National Portal of India">{{cite web|url=http://knowindia.gov.in/knowindia/national_symbols.php?id=8|title=National Aquatic Animal – National Symbols – Know India: National Portal of India|publisher=National Portal of India|access-date=23 March 2012|archive-url=https://web.archive.org/web/20130122081831/http://www.knowindia.gov.in/knowindia/national_symbols.php?id=8|archive-date=22 January 2013}}</ref><ref name="National Symbols of Pakistan">{{cite web|url=http://www.pakistan.gov.pk/national_symbols.html|title=National Symbols of Pakistan|publisher=Government of Pakistan|access-date=23 October 2016|archive-url=https://web.archive.org/web/20161128073024/http://www.pakistan.gov.pk/national_symbols.html|archive-date=28 November 2016}}</ref>

== See also ==
* [[Irrawaddy dolphin]]
* [[List of cetaceans]]
* ''[[Makara]]'' – water creature from [[Hindu mythology]] that is sometimes depicted dolphin-like
* [[Project Dolphin (India)]]

{{Portal bar|Cetaceans|Mammals|Marine life}}

==References==
{{Reflist|30em}}

== External links ==
* {{commons-inline}}

{{Cetacea|O.}}
{{Odontoceti|C.}}

{{Taxonbar|from1=Q950620}}
{{Authority Control}}

[[Category:South Asian river dolphins| ]]
[[Category:Apex predators]]
[[Category:Cetacean genera]]
[[Category:Mammals of South Asia]]
[[Category:Platanistidae]]
[[Category:Taxa named by Johann Georg Wagler]]
[[Category:Extant Quaternary first appearances]]