View source for River dolphin

{{Short description|Polyphyletic grouping of dolphins}}
{{good article}}
{{Use American English|date=October 2015}}
{{Infobox
 |abovestyle = background:#cfc;
 |subheaderstyle =
 |above        = River dolphins
 |subheader    = River dolphins are not a taxon, they are an informal grouping of the infraorder [[Cetacea]]
 |image        = 
 |caption      = Four major species of river dolphins
 |headerstyle  = background:#ccf;
 |labelstyle   = background:#ddf;
 |header1 = Information
 | label5 = Families considered river dolphins
 |  data5 =
* Parvorder [[Odontoceti]]
* Family [[Platanistidae]]
* Family (?†) [[Lipotidae]]
* Family [[Iniidae]]
* Family [[Pontoporiidae]]
 |label6 = New World range map
 |data6  = [[File:Inia range map PLoS ONE.jpg|New World river dolphin range map|200px]]
 |label7 = Old World range map
 |data7  = [[File:SouthAsianRiverDolphin distribution2019.png|Old World river dolphin range|200px]]
}}

'''River dolphins''' are a [[polyphyletic]] group of fully [[aquatic mammal]]s that reside exclusively in freshwater or [[brackish water]]. They are an informal grouping of [[dolphin]]s, which itself is a [[paraphyly|paraphyletic]] group within the infraorder [[Cetacea]]. Extant river dolphins are placed in two superfamilies, '''Platanistoidea''' and '''Inioidea'''. They comprise the families [[Platanistidae]] (the South Asian dolphins), the possibly extinct [[Lipotidae]] (Yangtze River dolphin), [[Iniidae]] (the Amazonian dolphins) and [[Pontoporiidae]]. There are five [[Neontology|extant]] species of river dolphins. River dolphins, alongside other cetaceans, belong to the clade [[Artiodactyla]], with [[even-toed ungulate]]s, and their closest living relatives the [[Hippopotamidae|hippopotamuses]], from which they diverged about 40 million years ago. Specific types of dolphins can be pink.<ref>{{Cite web|title=Amazon River Dolphin (Pink Dolphins) {{!}} Species {{!}} WWF|url=https://www.worldwildlife.org/species/amazon-river-dolphin|access-date=2021-04-21|website=World Wildlife Fund|language=en}}</ref>

River dolphins are relatively small compared to other dolphins, having evolved to survive in warm, shallow water and strong river currents. They range in size from the {{convert|5|ft|m|sp=us|adj=on}} long [[South Asian river dolphin]] to the {{convert|8|ft|m|sp=us|adj=on}} and {{convert|220|lb|kg|adj=on}} [[Amazon river dolphin]]. Several species exhibit [[sexual dimorphism]], in that the females are larger than the males. They have streamlined bodies and two limbs that are modified into flippers. River dolphins use their conical-shaped teeth and long beaks to capture fast-moving prey in murky water. They have well-developed hearing that is adapted for both air and water; they do not really rely on vision since their eyes are very small and the water they swim in is usually very muddy. Instead, they tend to rely on [[Animal echolocation|echolocation]] when hunting and navigating.  These species are well-adapted to living in warm, shallow waters, and, unlike other cetaceans, have little to no [[blubber]].

River dolphins are not very widely distributed; they are all restricted to certain rivers or deltas. This makes them extremely vulnerable to [[habitat destruction]]. River dolphins feed primarily on fish. Male river dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. River dolphins produce a variety of vocalizations, usually in the form of clicks and whistles.

River dolphins are rarely kept in captivity; breeding success has been poor and the animals often die within a few months of capture. {{as of|2020}}, there was only one river dolphin in captivity.<ref>{{Cite web |date=2020-12-22 |title=The last river dolphin |url=https://uk.whales.org/2020/12/22/the-last-river-dolphin/ |access-date=2023-09-15 |website=Whale & Dolphin Conservation UK |language=en-GB}}</ref>

==Taxonomy and evolution==

===Classification===
{{Main|List of cetaceans}}
Four [[family (biology)|families]] of river dolphins (Iniidae, Pontoporiidae, Lipotidae and Platanistidae) are currently recognized, comprising three superfamilies (Inioidea, Lipotoidea and Platanistoidea). Platanistidae, containing the two subspecies of [[South Asian river dolphin]], is the only living family in the superfamily Platanistoidea.<ref name="Rice1998">{{cite book|author=Rice, D. W.|title=Marine Mammals of the World: Systematics and Distribution|date=1 January 1998|pages=92–95|publisher=[[Society for Marine Mammalogy]]|isbn=978-1-891276-03-3|oclc= 40622084|url=http://www.marinemammalscience.org/wp-content/uploads/2014/09/MarineMammalsOfTheWorld.pdf}}</ref> Previously, many taxonomists had assigned all river dolphins to a single family, Platanistidae, and treated the Ganges and Indus river dolphins as separate species. A December 2006 survey found no members of ''[[Baiji|Lipotes vexillifer]]'' (commonly known as the baiji, or Chinese river dolphin) and declared the species [[functionally extinct]].<ref name=Turvey2007>{{cite journal|last1=Turvey|first1=S.T.|last2=Pitman|first2=R.L.|last3=Taylor|first3=B.L.|last4=Barlow|first4=J.|last5=Akamatsu|first5=T.|last6=Barrett|first6=L.A.|last7=Zhao|first7=X. |last8=Reeves |first8=R.R.|last9=Stewart|first9=B.S.|last10=Wang|first10=K.|last11=Wei|first11=Z.|last12=Zhang|first12=X.|last13=Pusser|first13=L.T.|last14=Richlen|first14=M.|last15=Brandon|first15=J.R.|last16=Wang|first16=D.|title=First human-caused extinction of a cetacean species?|journal=Biology Letters|date=2007|volume=3|issue=5|pages=537–540|doi=10.1098/rsbl.2007.0292|pmid=17686754|pmc=2391192}}</ref>

The current classification of river dolphins is as follows:<ref name="Rice1998" /><ref name=Rice2009>{{cite book |first1=Dale W. |last1=Rice |chapter=Classification (Overall) |title=Encyclopedia of Marine Mammals |edition=2nd |year=2009 |pages=234–238 |publisher=Academic Press |doi=10.1016/B978-0-12-373553-9.00058-4 |isbn=978-0-12-373553-9 |chapter-url=https://books.google.com/books?id=2rkHQpToi9sC&pg=PA234  }}</ref><ref name=Lee2012>{{cite journal | author = Lee, Y.| year = 2012 | title = First record of a platanistoid cetacean from the middle Miocene of South Korea | journal = Journal of Vertebrate Paleontology | volume = 32 | issue = 1 | pages = 231–234 | doi = 10.1080/02724634.2012.626005| bibcode = 2012JVPal..32..231L | s2cid = 129560068 |display-authors=etal}}</ref>
[[File:Arktocara NT small.jpg|thumb|Life reconstruction of ''[[Arktocara yakataga]]'', an [[Allodelphinidae|allodelphinid]]]]
* Superfamily Platanistoidea
** Family [[Platanistidae]]
*** Genus ''[[Platanista]]''
**** [[South Asian river dolphin]], ''Platanista gangetica'', with two subspecies
***** [[Ganges river dolphin]] (''susu''), ''P. g. gangetica''
***** [[Indus river dolphin]] (''bhulan''), ''P. g. minor''
** Family †[[Allodelphinidae]] ([[Oligocene]] - [[Miocene]])
** Family †[[Squalodelphinidae]] ([[Oligocene]] to Miocene)
** Family †[[Squalodontidae]] (Oligocene to Miocene)
** Family †[[Waipatiidae]] (Oligocene to Miocene)
* Superfamily Inioidea
** Family [[Iniidae]]
*** Genus ''[[Inia]]''[[File:NOVO AIRÃO.JPG|thumb|[[Amazon river dolphin]]]]
**** [[Amazon river dolphin]] (''boto''), ''Inia geoffrensis''
***** ''Inia geoffrensis geoffrensis''
***** ''Inia geoffrensis humbotiana''
**** [[Araguaian river dolphin]], ''Inia araguaiaensis''
**** [[Bolivian river dolphin]], ''Inia boliviensis''
*** Genus †''[[Meherrinia]]'' (late Miocene)
*** Genus †''[[Isthminia panamensis|Isthminia]]'' (Miocene)
** Family [[Pontoporiidae]]
*** Genus †''[[Auroracetus]]''
**** †''Auroracetus bakerae''
*** Genus ''[[La Plata dolphin|Pontoporia]]''
**** [[La Plata dolphin]] (''Franciscana''), ''Pontoporia blainvillei''
* Superfamily [[Lipotoidea]]
** Family [[Lipotidae]]
*** Genus ''[[Lipotes]]''
**** ''[[Baiji]]'' (or Chinese river dolphin), ''Lipotes vexillifer''

In 2012 the [[Society for Marine Mammalogy]] began considering the Bolivian (''Inia geoffrensis boliviensis'') and Amazonian (''Inia geoffrensis geoffrensis'') subspecies as full species ''Inia boliviensis'' and ''Inia geoffrensis'', respectively; however, much of the scientific community, including the [[IUCN]], continue to consider the Bolivian population to be a subspecies of ''Inia geoffrensis''.<ref name="MMS">{{cite web|url=https://www.marinemammalscience.org/species-information/list-of-marine-mammal-species-subspecies/|author=Committee on Taxonomy|date=2012|title=List of marine mammal species and subspecies|publisher=Society for Marine Mammalogy|access-date=January 24, 2014|archive-url=https://web.archive.org/web/20150106152733/https://www.marinemammalscience.org/species-information/list-of-marine-mammal-species-subspecies/|archive-date=January 6, 2015}}</ref><ref name="iucn">Reeves, R.R., Jefferson, T.A., Karczmarski, L., Laidre, K., O'Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. (2011). ''Inia geoffrensis''. The IUCN Red List of Threatened Species {{doi|10.2305/IUCN.UK.2011-1.RLTS.T10831A3220342.en}}</ref>

In October 2014, the Society for Marine Mammalogy took ''Inia boliviensis'' and ''Inia araguaiaensis'' off their list of [[aquatic mammal]] species and subspecies and currently does not recognize these species-level separations.<ref name="MMS"/><ref>{{cite journal|url=https://www.marinemammalscience.org/species-information/list-of-marine-mammal-species-subspecies/|title=List of Marine Mammal Species and Subspecies|publisher=Society of Mammalogy|date=October 2014|access-date=September 19, 2015|archive-url=https://web.archive.org/web/20150106152733/https://www.marinemammalscience.org/species-information/list-of-marine-mammal-species-subspecies/|archive-date=January 6, 2015}}</ref>

===Evolution===
{{Further|Evolution of cetaceans}}
[[File:Cetacean phylogeny PLoS ONE 2014-01-22.png|thumb|320px|Phylogeny of cetaceans based on [[cytochrome b]] gene sequences, showing the distant relationship between ''[[Platanista]]'' and other river dolphins.]]
River dolphins are members of the infraorder [[Cetacea]], which are descendants of land-dwelling mammals of the [[order (biology)|order]] [[Artiodactyla]] (even-toed [[ungulate]]s). They are related to the ''[[Indohyus]]'', an extinct [[chevrotain|chevrotain-like]] ungulate, from which they split approximately 48 million years ago.<ref name="Ancestors_Tale">{{cite book |first=Richard |last=Dawkins |author-link=Richard Dawkins |title=The Ancestor's Tale, A Pilgrimage to the Dawn of Life |title-link=The Ancestor's Tale |publisher=Houghton Mifflin |year=2004 |pages=196–203 |isbn=978-0-618-00583-3}}</ref>
The primitive cetaceans, or [[archaeocetes]], first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later. It is unknown when river dolphins first ventured back into fresh water.<ref>{{cite newsgroup|url=http://phenomena.nationalgeographic.com/2015/09/09/fossil-river-dolphin-lived-out-at-sea/|archive-url=https://web.archive.org/web/20150910073803/http://phenomena.nationalgeographic.com/2015/09/09/fossil-river-dolphin-lived-out-at-sea/|archive-date=September 10, 2015|last=Switek|first=Brian|title=Fossil "River Dolphin" Lived Out at Sea|date=9 September 2015|access-date= 2 November 2015}}</ref>

River dolphins are thought to have relictual distributions, that is, their ancestors originally occupied marine habitats, but were then displaced from these habitats by modern dolphin lineages.<ref name=Cassens2000>{{cite journal|last1=Cassens|first1=I.|last2=Vicario|first2=S.|last3=Waddell|first3=V.G.|last4=Balchowsky|first4=H.|last5=Van Belle|first5=D.|last6=Ding|first6=W.|last7=Fan|first7=C.|last8=Mohan|first8=R.S.|last9=Simões-Lopes|first9=P.C.|last10=Bastida|first10=R.|last11=Meyer|first11=A.|last12=Stanhope|first12=M.J.|last13=Milinkovitch|first13=M.C.|title=Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages|journal=Proceedings of the National Academy of Sciences of the United States of America|date=2000|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=Hamilton2001>{{cite journal|last1=Hamilton|first1=H.|last2=Caballero|first2=S.|last3=Collins|first3=A. G.|last4=Brownell|first4=R. L.|title=Evolution of river dolphins|journal=[[Proceedings of the Royal Society B: Biological Sciences]]|date=2001|volume=268|issue=1466|pages=549–556|doi=10.1098/rspb.2000.1385|pmid=11296868|pmc=1088639}}</ref> Many of the [[Morphology (biology)|morphological]] similarities and adaptations to freshwater habitats arose due to [[convergent evolution]]; thus, a grouping of all river dolphins is [[polyphyly|polyphyletic]]. Amazon river dolphins are actually more closely related to [[Delphinoidea|oceanic dolphins]] than to [[South Asian river dolphin]]s.<ref name="Hrbek2014">{{cite journal|last1=Hrbek|first1=T.|last2=da Silva|first2=V.M.F.|last3=Dutra|first3=N.|last4=Gravena|first4=W.|last5=Martin|first5=A.R.|last6=Farias|first6=I.P.|last7=Turvey|first7=S.T.|title=A New Species of River Dolphin from Brazil or: How Little Do We Know Our Biodiversity|journal=[[PLoS ONE]]|date=2014|volume=9|issue=1|article-number=e83623|doi=10.1371/journal.pone.0083623|pmid=24465386|pmc=3898917|bibcode=2014PLoSO...983623H|doi-access=free}}</ref> ''[[Isthminia panamensis]]'' is an extinct genus and species of river dolphin, living 5.8 to 6.1 million years ago. Its fossils were discovered near Piña, Panama.<ref>{{Cite web|last1=Gibbons|first1=Johnny| title = Fossil Specimen Reveals a New Species of Ancient River Dolphin|url = http://smithsonianscience.si.edu/2015/09/fossil-specimen-reveals-a-new-species-of-ancient-river-dolphin-to-smithsonian-scientists/|work=Smithsonian Science News|date=September 1, 2015|access-date = September 1, 2015}}</ref><ref>{{cite journal|last1=Pyenson|first1=N.D.|last2=Vélez-Juarbe|first2=J.|last3=Gutstein|first3=C.S.|last4=Little|first4=H.|last5=Vigil|first5=D.|last6=O'Dea|first6=A.|title=''Isthminia panamensis'', a new fossil inioid (Mammalia, Cetacea) from the Chagres Formation of Panama and the evolution of 'river dolphins' in the Americas|journal=PeerJ|date=2015|volume=3|article-number=e1227|doi=10.7717/peerj.1227|pmid=26355720|pmc=4562255 |doi-access=free }}</ref>

River dolphin has been considered a taxonomic description, suggesting an evolutionary relationship among the group, although it is now known that they form two distinct clades. 'True' river dolphins are descendants of ancient evolutionary lineages that evolved in freshwater environments.<ref name=Cassens2000/>

Some species of cetacean live in rivers and lakes, but are more closely related to [[oceanic dolphins]] or [[porpoises]] and entered fresh water more recently. Such species are considered facultative freshwater cetaceans as they can use both marine and freshwater environments. These include species such as the [[Irrawaddy dolphin]], ''Orcaella brevirostris'', found in the [[Mekong]], [[Mahakam]], the [[Irrawaddy River]]s, as well as the [[Yangtze finless porpoise]] ''Neophocaena asiaeorientalis''.<ref>{{cite book|url=https://books.google.com/books?id=rHVFBAAAQBAJ&q=irrawady+dolphin+distribution+and+habitat&pg=PA41|first1=Brian D.|last1=Smith|first2=William F.|last2=Perrin|title=Distribution, Mortality, Diet and Conservation of Irrawaddy Dolphins (''Orcaella Brevirostris'') In Lao PDR|journal= Asian Marine Biology|year=1997|volume=14|pages=41–48|isbn=978-962-209-462-8}}</ref> Some oceanic cetacean populations are known to live semi-permanently in river and [[Estuary|estuarine]] systems, such as the [[Indo-Pacific bottlenose dolphin]] group resident in the [[Swan River (Western Australia)|Swan River]] of [[Western Australia]] which travel as far inland as [[Belmont, Western Australia|Belmont]].<ref>{{Cite web|url=http://www.wabiz.org/a-z/s/swan-river/dolphins|title = Dolphins on the Swan River - WA Achievers}}</ref>

The [[tucuxi]] (''Sotalia fluviatilis'') in the [[Amazon River]] is another species descended from oceanic dolphins; however, it does not perfectly fit the label of 'facultative' either, as it occurs only in fresh water. The tucuxi was until recently considered conspecific with the [[Guiana dolphin]] (''Sotalia guianensis''), which inhabits marine waters. It may also be true for the Irrawaddy dolphin and the finless porpoise that, although the species may be found in both freshwater and marine environments, individual animals found in rivers may not be able to survive in the ocean, and vice versa.<ref>{{cite journal|first1=H.A.|last1=Cunha|first2=V.M.F.|last2=da Silva|first3=J. Jr |last3=Lailson-Brito|first4=M.C.O.|last4=Santos|first5=P.A.C.|last5=Flores|first6=A.R.|last6=Martin|first7=A.F.|last7=Azevedo|first8=A.B.L.|last8=Fragoso|first9=R.C.|last9=Zanelatto|first10=A.M.|last10=Solé-Cava|title=Riverine and marine ecotypes of ''Sotalia'' dolphins are different species|journal=Marine Biology|year=2005|volume=148|issue=2|pages=449–457|doi=10.1007/s00227-005-0078-2|bibcode=2005MarBi.148..449C |s2cid=49359327}}</ref> The tucuxi is currently classified as an oceanic dolphin (Delphinidae).<ref>Secchi, E. (2012). ''Sotalia fluviatilis''. The IUCN Red List of Threatened Species {{doi|10.2305/IUCN.UK.2012.RLTS.T190871A17583369.en}}</ref>

The [[Franciscana]] (''Pontoporia blainvillei'') has shown a converse evolutionary pattern, and has an ancient evolutionary lineage in freshwater, but inhabits estuarine and coastal waters.<ref>{{cite journal|first1=Enrique A. |last1=Crespo|first2=Guillermo|last2=Harris|first3=Raúl|last3=González|title=Group size and distribution of the franciscana, ''Pontoporia blainvellei''|journal=Marine Mammal Science|year=1998|volume=14|issue=4|pages=845–849|doi=10.1111/j.1748-7692.1998.tb00768.x |bibcode=1998MMamS..14..845C }}</ref>

==Biology==

===Anatomy===
[[File:Indus River dolphin skull cast.jpg|thumb|[[Indus river dolphin]] skull]]

River dolphins have a torpedo shaped body with a flexible neck, limbs modified into flippers, non-existent external ear flaps, a tail fin, and a small bulbous head. River dolphin skulls have small eye orbits, a long snout  and eyes placed on the sides of the head. River dolphins are rather small, ranging in size from the {{convert|5|ft|m|sp=us|adj=on}} long [[South Asian river dolphin]] to the {{convert|8|ft|m|sp=us|adj=on}} and {{convert|220|lbs|kg|adj=on}} [[Amazon river dolphin]]. They all have female-biased [[sexual dimorphism]] apart from Amazon river dolphin, with the females being larger than the males.<ref>{{cite book |url=http://www.cetus.ucsd.edu/SIO133/PDF/Sexual%20Dimorphism.pdf |title=Sexual Dimorphism |author1=Ralls, Katherine |author2=Mesnick, Sarah |pages=1005–1011 |access-date=2015-09-12 |archive-date=2019-07-25 |archive-url=https://web.archive.org/web/20190725004132/http://www.cetus.ucsd.edu/SIO133/PDF/Sexual%20Dimorphism.pdf }}</ref><ref name="Cetacean anatomy">{{cite journal|last1=Reidenberg|first1=Joy S.|title=Anatomical adaptations of aquatic mammals|journal=The Anatomical Record|date=2007|volume= 290|issue=6|pages=507–513|doi=10.1002/ar.20541|pmid=17516440|s2cid=42133705|doi-access=free}}</ref> River dolphins are [[polygynous]], meaning male river dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them.<ref name="Cetacean anatomy"/>

River dolphins have conical teeth, used to catch swift prey such as small river fish.<ref name="Cetacean anatomy"/> They also have very long snouts, with some measuring {{convert|23|in|cm|sp=us}}, four times longer than most of their [[oceanic dolphin|oceanic counterparts]]. They have a two-chambered stomach that is similar in structure to that of terrestrial carnivores. They have [[Fundic stomach|fundic]] and [[Pyloric stomach|pyloric]] chambers.<ref>{{cite book |author1=Stevens, C. Edward |author2=Hume, Ian D. |isbn=978-0-521-61714-7|title=Comparative Physiology of the Vertebrate Digestive System |url=https://archive.org/details/comparativephysi0000stev |url-access=registration |publisher=Cambridge University Press |page=[https://archive.org/details/comparativephysi0000stev/page/317 317] |year=1995}}</ref> Breathing involves expelling stale air from their [[blowhole (anatomy)|blowhole]], followed by inhaling fresh air into their lungs. They do not have the iconic [[Blowhole (anatomy)|spout]], as this only forms when the warm air exhaled from the lungs meets cold external air, which does not occur in their tropical habitats.<ref name="Cetacean anatomy"/><ref>{{cite journal |last1=Scholander |first1=Per Fredrik |title=Experimental investigations on the respiratory function in diving mammals and birds |year=1940 |journal=Hvalraadets Skrifter |volume=22 |pages=1–131}}</ref>

River dolphins have a relatively thin layer of [[blubber]]. Blubber can help with buoyancy, protection from predators (they would have a hard time getting through a thick layer of fat), energy for leaner times, and insulation from harsh climates. The habitats of river dolphins lack these needs.<ref name="Cetacean anatomy"/>

===Locomotion===

River dolphins have two flippers and a tail fin. These flippers contain five digits. Although river dolphins do not possess fully developed hind limbs, some possess discrete rudimentary appendages, which may contain feet and digits. River dolphins are slow swimmers in comparison to oceanic dolphins, which can travel at speeds up to {{convert|35|mph|kph|sp=us}}; the [[tucuxi]] can only travel at about {{convert|14|mph|kph|sp=us}}.<ref>{{cite journal|url=http://www.bio-nica.info/biblioteca/Edwards2001.pdf|last1=Edwards|first1=Holly H.|last2=Schnell|first2=Gary D.|title=Body Length, Swimming Speed, Dive Duration, and Coloration of the Dolphin ''Sotalia fluviatilis'' (Tucuxi) in Nicaragua|journal=Caribbean Journal of Science|volume=37|pages=271–298|year=2001}}</ref> Unlike other cetaceans, their neck vertebrae are not fused together, meaning they have greater flexibility than other non-terrestrial [[aquatic mammal]]s, at the expense of speed. This means they can turn their head without actually moving their entire body.<ref>{{cite journal|url=http://acsonline.org/fact-sheets/boto-amazon-river-dolphin/|title=Boto (Amazon river dolphin) ''Inia geoffrensis''|journal=American Cetacean Society|year=2002|access-date=September 12, 2015}}</ref><ref>{{cite book|chapter-url=https://books.google.com/books?id=ASIVAAAAIAAJ&q=whales+have+a+fused+neck+vertebrae&pg=PA37|last=Tinker|first=Spencer|title=Whales of the World|chapter=The Vertebrae of the Cervical Region|page=[https://archive.org/details/whalesofworld00tink/page/37 37]|isbn=978-0-935848-47-2|date=1988-01-01|publisher=Brill Archive |url-access=registration|url=https://archive.org/details/whalesofworld00tink/page/37}}</ref> When swimming, river dolphins rely on their tail fins to propel themselves through the water. Flipper movement is continuous. River dolphins swim by moving their tail fins and lower bodies up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. All species have a [[dorsal fin]].<ref name="Cetacean anatomy"/>

===Senses===
[[File:Delfinekko.gif|thumb|right|[[Biosonar]] by cetaceans]]
[[File:Inia geofrensis río Negro.jpg|thumb|River dolphins have very small eyes]]

The ears of river dolphins have specific adaptations to their aquatic environment. In humans, the [[middle ear]] works as an impedance equalizer between the outside air's low [[Acoustic impedance|impedance]] and the [[cochlea]]r fluid's high impedance. In river dolphins, and other cetaceans, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, river dolphins receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The ear is acoustically isolated from the skull by air-filled sinus pockets, which allows for greater directional hearing underwater.<ref>{{cite journal|last1=Nummela|first1=S.|last2=Thewissen|first2=J.G.|last3=Bajpai|first3=S.|last4=Hussain|first4=T.|last5=Kumar|first5=K.|title=Sound transmission in archaic and modern whales: anatomical adaptations for underwater hearing.|journal=The Anatomical Record|date=2007|volume=290|issue=6|pages=716–733|doi=10.1002/ar.20528|pmid=17516434|s2cid=12140889|url=http://repository.ias.ac.in/4651/1/321.pdf|doi-access=free}}</ref> Dolphins send out high frequency clicks from an organ known as a [[melon (cetacean)|melon]]. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. This allows river dolphins to produce [[biosonar]] for orientation.<ref name="Cetacean anatomy"/><ref name="Thomas">{{cite book |editor1=Thomas, Jeanette A. |editor2=Kastelein, Ronald A. |title=Sensory Abilities of Cetaceans: Laboratory and Field Evidence |volume=196 |isbn=978-1-4899-0860-5 |doi=10.1007/978-1-4899-0858-2 |year=2002 |url=https://books.google.com/books?id=VWz1BwAAQBAJ&q=cetacean+senses&pg=PA1|publisher=Springer Science & Business Media|s2cid=32801659 }}</ref>{{rp|203–427}}<ref name="Thewissen-Hearing">{{cite book |last=Thewissen |first=J. G. M. |chapter=Hearing |pages=[https://archive.org/details/encyclopediaofma2002unse/page/570 570–572] |title=Encyclopedia of Marine Mammals |editor1-last=Perrin |editor1-first=William R. |editor2-last=Wirsig |editor2-first=Bernd |editor3-last=Thewissen |editor3-first=J.G.M. |year=2002 |publisher=Academic Press |isbn=978-0-12-551340-1 |chapter-url=https://archive.org/details/encyclopediaofma2002unse/page/570 }}</ref><ref>{{cite book |last=Ketten |first=Darlene R.|chapter=The Marine Mammal Ear: Specializations for Aquatic Audition and Echolocation |title=The Evolutionary Biology of Hearing |editor1-last=Webster |editor1-first=Douglas B. |editor2-last=Fay |editor2-first=Richard R. |editor3-last=Popper |editor3-first=Arthur N. |year=1992 |publisher=Springer |chapter-url=https://www.researchgate.net/publication/230691464 |pages=725–727|doi=10.1007/978-1-4612-2784-7_44|isbn=978-1-4612-7668-5}}</ref> They are so dependent on echolocation that they can survive even if they are blind.<ref>{{cite journal|last1=Herald|first1=E.S.|last2=Brownell RL|first2=J.|last3=Frye|first3=F.L.|last4=Morris|first4=E.J.|last5=Evans|first5=W.E.|last6=Scott|first6=A.B.|title=Blind river dolphin: first side-swimming cetacean|journal=Science|date=1969|volume=166|issue=3911|pages=1408–1410|doi=10.1126/science.166.3911.1408|pmid=5350341|bibcode=1969Sci...166.1408H|s2cid=5670792|url=https://digitalcommons.unl.edu/usdeptcommercepub/138|url-access=subscription}}</ref> Beyond locating an object, echolocation also provides the animal with an idea on the object's shape and size, though how exactly this works is not yet understood. The small hairs on the rostrum of the Amazon river dolphin are believed to function as a [[somatosensory system|tactile sense]], possibly to compensate for their poor eyesight.<ref>{{cite web|title= Amazon River Dolphin (''Inia geoffrensis'')|first=Laurie|last=Stepanek|date=May 19, 1998|publisher=Texas Marine Mammal Stranding Network|url=http://www.tmmsn.org/mmgulf/inia_geoffrensis.html|access-date= November 20, 2013 |archive-url = https://web.archive.org/web/20070206051622/http://www.tmmsn.org/mmgulf/inia_geoffrensis.html |archive-date = February 6, 2007}}</ref>

River dolphins have very small eyes for their size, and do not have a very good sense of sight.<ref name="Rice1998" /> In addition, the eyes are placed on the sides of the head, so the vision consists of two fields, rather than a [[binocular vision|binocular]] view like humans have. When river dolphins surface, their lens and cornea correct the nearsightedness that results from the refraction of light.<ref name="Mass07"/> They have both [[rod cell|rod]] and [[cone cell|cone]] cells, meaning they can see in both dim and bright light.<ref name="Mass07">{{cite journal |last1=Mass |first1=Alla M. |last2=Supin |first2=Alexander, Y. A. |title=Adaptive features of aquatic mammals' eyes |journal=Anatomical Record |volume=290 |issue=6 |pages=701–715 |date=May 21, 2007 |doi=10.1002/ar.20529 |pmid=17516421|s2cid=39925190 |doi-access=free }}</ref> Most river dolphins have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a  [[tapetum lucidum]]; these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. They also have glands on their eyelids and an [[corneal epithelium|outer corneal layer]] that act as protection for the cornea.<ref name="Thomas"/>{{rp|505–519}}

[[Olfactory lobes]] are absent in river dolphins, suggesting that they have no sense of smell.<ref name="Thomas"/>{{rp|481–505}}

River dolphins are not thought to have a sense of taste, as their taste buds are atrophied or missing altogether.  However, some dolphins have preferences between different kinds of fish, indicating some sort of attachment to taste.<ref name="Thomas"/>{{rp|447–454}}

==Interactions with humans==

===Threats===

====Development====
{{See also|Baiji#Conservation}}
[[File:Baiji conservation efforts map.png|thumb|340px|Conservation areas for the [[baiji]] along the [[Yangtze River]]]]
Development and agriculture have had devastating impacts on the habitats on river dolphins. The total population of [[Araguaian river dolphin]]s is estimated to be between 600 and 1,500 individuals, and [[genetic diversity]] is limited.<ref name="Hrbek2014"/> The ecology of their habitat has been adversely affected by agricultural, ranching and industrial activities, as well as by the use of dams for hydroelectric power. The inhabited section of the Araguaia River probably extends over about {{convert|900|mi|km}} out of a total length of {{convert|1300|mi|km}}. The [[Tocantins river]] habitat is [[Habitat fragmentation|fragmented]] by six hydroelectric dams, so the population there is at particular risk.<ref name="Hrbek2014"/> Its probable eventual [[IUCN]] status is [[Vulnerable species|vulnerable]] or worse.<ref name="Hrbek2014"/><ref name="Dolphins">{{cite book |last1=Klinowska  |first1=Margaret |last2=Cooke |first2=Justin |year=1991 |title=Dolphins, Porpoises, and Whales of the World: the IUCN Red Data Book |url=https://portals.iucn.org/library/sites/library/files/documents/RD-1991-001.pdf}}</ref>{{rp|54–58}}

Both subspecies of [[South Asian river dolphin]]s have been very adversely affected by human use of the river systems in the [[Indian subcontinent|subcontinent]]. Irrigation has lowered water levels throughout both subspecies' ranges. Poisoning of the water supply from industrial and [[agrochemical|agricultural chemicals]] may have also contributed to population decline. Perhaps the most significant issue is the building of more than 50 dams along many rivers, causing the segregation of populations and a narrowed [[gene pool]] in which the dolphins can breed. Currently, three subpopulations of Indus river dolphins are considered capable of long-term survival if protected.<ref name="Dolphins"/>{{rp|31–32, 37–38}}<ref name=Braulik>{{cite journal | last1=Braulik |first1=G. T. |date=2006 | title = Status assessment of the Indus river dolphin, ''Platanista minor minor'', March–April 2001 | journal = Biological Conservation | volume = 129 |issue=4|pages = 579–590 | doi = 10.1016/j.biocon.2005.11.026}}</ref>

As China developed economically, pressure on the [[baiji|baiji river dolphin]] grew significantly.<ref name="Dolphins"/>{{rp|41–46}} [[Industrial waste|Industrial]] and residential waste flowed into the Yangtze. The riverbed was dredged and reinforced with concrete in many locations. Ship traffic multiplied, boats grew in size, and fishermen employed wider and more lethal nets. Noise pollution caused the nearly blind animal to collide with propellers. Stocks of the dolphin's prey declined drastically in the late 20th century, with some fish populations declining to one thousandth of their pre-industrial levels.<ref name=BBC>{{cite newsgroup|author=Black, Richard |url= https://news.bbc.co.uk/2/hi/science/nature/5122074.stm|title = Last Chance for China's Dolphin|date=June 27, 2006|access-date=June 27, 2006|url-status=live |archive-url=https://web.archive.org/web/20060706045903/http://news.bbc.co.uk/2/hi/science/nature/5122074.stm|archive-date= July 6, 2006 }}</ref> In the 1950s, the population was estimated at 6,000 animals,<ref>{{cite newsgroup|url= http://www.china.org.cn/english/environment/36657.htm|title=Rescue Plan Prepared for Yangtze River Dolphins|date=July 11, 2002|access-date=December 18, 2006}}</ref> but declined rapidly over the subsequent five decades. Only a few hundred were left by 1970. Then the number dropped down to 400 by the 1980s and then to 13 in 1997 when a full-fledged search was conducted. On December 13, 2006, the [[baiji]] (''Lipotes vexillifer'') was declared "functionally extinct", after a 45-day search by leading experts in the field failed to find a single specimen. The last verified and widely accepted sighting was in September 2004, but it has been allegedly seen and photographed by Chinese citizens on four occasions since then.<ref name=Turvey2007/><ref>{{Cite web |title=中华白鱀豚功能性灭绝十年后疑似重现长江，科考队称拍到两头_绿政公署_澎湃新闻-The Paper |url=https://m.thepaper.cn/wifiKey_detail.jsp?contid=1684992&from=wifiKey# |access-date=2024-11-13 |website=m.thepaper.cn}}</ref><ref>{{Cite web |title=The Search for the Baiji |url=https://www.theworldofchinese.com/2019/02/the-search-for-the-river-goddess/ |access-date=2024-11-13 |website=The World of Chinese |language=en}}</ref>

====Competition====
{{Main|Amazon river dolphin#Human interaction}}
The region of the Amazon in Brazil has an extension of {{convert|3,100,000|mi2|km2|abbr=on|sp=us}} containing diverse fundamental ecosystems.<ref name="Silvano et al., 2009">{{cite journal|last1=Silvano|first1=R.A.M.|last2=Ramires|first2=M.|last3=Zuanon|first3=J.|title=Effects of fisheries management on fish communities in the floodplain lakes of a Brazilian Amazonian Reserve|journal=Ecology of Freshwater Fish|date=2009|volume=18|issue=1 |pages=156–166|doi=10.1111/j.1600-0633.2008.00333.x|bibcode=2009EcoFF..18..156S }}</ref><ref>{{cite journal|last1=Barletta|first1=M.|last2=Jaureguizar|first2=A.J.|last3=Baigun|first3=C.|last4=Fontoura|first4=N.F.|last5=Agostinho|first5=A.A.|last6=Almeida-Val|first6=V.M.F.|last7=Val|first7=A.L.|last8=Torres|first8=R.A.|last9=Jimenes-Segura|first9=L.F.|last10=Giarrizzo|first10=T.|last11=Fabré|first11=N.N.|last12=Batista|first12=V.S.|last13=Lasso|first13=C.|last14=Taphorn|first14=D.C.|last15=Costa|first15=M.F.|last16=Chaves|first16=P.T.|last17=Vieria|first17=J.P.|last18=Corrêa|first18=M.F.M.|title=Fish and aquatic habitat conservation in South America: A continental overview with an emphasis on Neotropical systems|journal=Journal of Fish Biology|volume=76|issue=9|pages=2118–2176|doi=10.1111/j.1095-8649.2010.02684.x|pmid=20557657|year=2010|bibcode=2010JFBio..76.2118B |url=http://repositorio.furg.br/handle/1/1948|url-access=subscription}}</ref> One of these ecosystems is a [[floodplain]], or a [[várzea forest]], and is home to a large number of fish species which are an essential resource for human consumption.<ref name="Iriarte 2013">{{cite journal|last1=Iriarte|first1=V.|last2=Marmontel|first2=M.|title=River Dolphin (''Inia geoffrensis'', ''Sotalia fluviatilis'') Mortality Events Attributed to Artisanal Fisheries in the Western Brazilian Amazon|journal=Aquatic Mammals|year=2013|volume=39|issue=2|pages=116–124|doi=10.1578/am.39.2.2013.116 |bibcode=2013AqMam..39..116I }}</ref> The várzea is also a major source of income through excessive local commercialized fishing.<ref name="Silvano et al., 2009"/><ref>{{cite journal|last1=Isaac|first1=V.J.|last2=Ruffino|first2=M.L.|title=Evaluation of fisheries in Middle Amazon|journal=American Fisheries Society Symposium|year=2007|volume=49|pages=587–596}}</ref><ref>{{cite book|last1=Neiland|first1=A.E.|last2=Benê|first2=C.|title=Tropical River Fisheries Valuation:Background papers to a global synthesis|year=2008|publisher=The World Fish Center|location=Penang, Malaysia|page=290}}</ref> Várzea consist of muddy river waters containing a vast number and diversity of nutrient-rich species.<ref name="171.66.127.192">{{cite journal|last1=Martin|first1=A.R.|last2=Da Silva|first2=V.M.F.|last3=Rothery|first3=P|year=2008|title=Object carrying as social–sexual display in an aquatic mammal|journal=Biology Letters|volume=4|issue=3|pages=1243–2145|doi=10.1098/rsbl.2008.0067|pmid=18364306|pmc=2610054}}</ref> The abundance of distinct fish species lures the Amazon River dolphin into the várzea areas of high water occurrences during the seasonal flooding.<ref>{{cite journal|last1=Arraut|first1=E.M.|first2=M.|last2=Marmontel|first3=J.E.|last3=Mantovani|first4=E.M.|last4=Novo|first5=D.W.|last5=Macdonald|first6=R.E.| last6=Kenward|year=2009|title=The lesser of two evils: seasonal migrations of Amazonian manatees in the Western Amazon|journal= Journal of Zoology|volume=280|number=3|pages=247–256|doi=10.1111/j.1469-7998.2009.00655.x}}</ref>

In addition to attracting predators such as the Amazon river dolphin, these high-water occurrences are an ideal location to draw in the local fisheries.<ref name="Dolphins"/>{{rp|54–58}} Human fishing activities directly compete with the dolphins for the same fish species, the [[tambaqui]] (''Colossoma macropomum'') and the [[Piaractus brachypomus|pirapitinga]] (''Piaractus brachypomus''), resulting in deliberate or unintentional catches of the Amazon river dolphin.<ref>{{cite book|last1=Reeves|first1=R.R.|last2=Smith|first2=B.D.|last3=Crespo|first3=E.A.|last4=Notarbartolo di Sciara|first4=G.|title=Dolphins, whales and porpoises: 2002–2010 conservation action plan for the world's cetaceans|year=2003|publisher=International Union for Conservation of Nature/Species Survival Committee|location=Gland, Switzerland, and Cambridge, UK|page=139}}</ref><ref name="Martin 2004">{{cite journal|last1=Martin|first1=A.R.|last2=Da Silva|first2=V.M.F.|last3=Rothery|first3=P.|title=Number, seasonal movements, and residency characteristics of river dolphins in an Amazonian floodplain lake system|journal=Canadian Journal of Zoology|date=2008|volume=82|issue=8|pages=1307–1315|doi=10.1139/z04-109}}</ref><ref name="Loch 2009">{{cite journal|last1=Loch|first1=Carolina|last2=Marmontel|first2=Miriam|last3=Simões-Lopes|first3=Paulo C.|title=Conflicts with fisheries and intentional killing of freshwater dolphins (Cetacea: Odontoceti) in the Western Brazilian Amazon|journal=Biodiversity and Conservation|date=2009|volume=18|issue=14|pages=3979–3988|doi=10.1007/s10531-009-9693-4|bibcode=2009BiCon..18.3979L |s2cid=20873255|issn=1572-9710}}</ref><ref name="Silvano et al., 2009"/><ref>{{cite book|last1=Beltrán-Pedreros|first1=S.|last2=Filgueiras-Henriques|first2=L.A.|title=Biology, evolution and conservation of river dolphins within South America and Asia|year=2010|publisher=[[Nova Science Publishers, Inc.]]|location=New York|pages=237–246}}</ref><ref name="Crespo 2010b">{{cite journal|last1=Crespo|first1=E.A.|last2=Alarcon|first2=D.|last3=Alonso|first3=M.|last4=Bazzalo|first4=M.|last5=Borobia|first5=M.|last6=Cremer|first6=M.|last7=Filla|first7=G.F.|last8=Lodi|first8=L.|last9=Magalhães|first9=F.A.|last10=Marigo|first10=J.|last11=Queiróz|first11=H.L.|last12=Reynolds|first12=J.E. III|last13=Schaeffer|first13=Y.|last14=Dorneles|first14=P.R.|last15=Lailson-Brito|first15=J.|last16=Wetzel|first16=D.L.|title=Report on the working group on major threats and conservation|journal=The Latin American Journal of Aquatic Mammals|year=2010|volume=8|issue=1–2|pages=47–56|doi=10.5597/lajam00153|doi-access=free|hdl=11336/98669|hdl-access=free}}</ref><ref name="Iriarte & Marmontel 2011">{{cite journal|last1=Iriarte|first1=V.|last2=Marmontel|first2=M.|title=Report of an encounter with a human intentionally entagled Amazon river dolphin (''Inia geoffrensis'') calf and its release in Tefé River, Amazonas State, Brazil|journal=Uakari|year=2011|volume=7|issue=2|pages=47–56}}</ref><ref name="Alves 2012">{{cite journal|last1=Alves|first1=L.C.P.S.|last2=Andriolo|first2=A.|last3=Zappes|first3=C.A.|title=Conflicts between river dolphins (Cetacea:Odontoceti) and fisheries in the Central Amazon: A path toward tragedy?|journal=Zoologia|year=2012|volume=29|issue=5|pages=420–429|doi=10.1590/s1984-46702012000500005|doi-access=free}}</ref> The local fishermen overfish, and when the Amazon river dolphins remove the commercialized fish from the nets and lines, it damages the equipment and the capture and causes a negative reaction from the local fishermen.<ref name="Loch 2009"/>
<ref name="Crespo 2010b"/><ref name="Iriarte & Marmontel 2011"/> The [[Brazilian Institute of Environment and Renewable Natural Resources]] prohibit fishermen from killing the Amazon river dolphin, yet they are not compensated for the damage to their equipment and the loss of their catch.<ref name="Alves 2012"/>

====Bycatch====
During the process of catching the commercialized fish, the Amazon river dolphins get caught in the nets and exhaust themselves until they die, or the local fishermen deliberately kill the dolphins that become entangled in their nets.<ref name="Iriarte 2013"/> The carcasses are discarded, consumed, or used as bait to attract a scavenger catfish, the [[piracatinga]] (''Calophysus macropterus'').<ref name="Iriarte 2013"/><ref name="Estupiñán">{{cite web|last1=Estupiñán|first1=G.|last2=Marmontel|first2=M.|last3=Queiroz|first3=H.L.|last4=Roberto e Souza|first4=P.|last5=Valsecchi|first5=J.|last6=da Silva Batista|first6=G.|last7=Barbosa Pereira|first7=S.|title=A pesca da piracatinga (''Calophysus macropterus'') na Reserva de Desenvolvimiento Sustentável Mamirauá [The piracatinga fishery (''Calophysus macropterus'') at Mamirauá Sustainable Development Reserve].|url=http://site-antigo.socioambiental.org/website/noticias/agenda/fks/rel_piracatinga.htm|publisher=Brazilian Ministry of Science and Technology|language=es|access-date=July 16, 2014|archive-date=July 28, 2014|archive-url=https://web.archive.org/web/20140728110821/http://site-antigo.socioambiental.org/website/noticias/agenda/fks/rel_piracatinga.htm}}</ref> The use of the Amazon river dolphin carcass as bait for the piracatinga dates back from 2000.<ref name="Estupiñán"/> The increasing consumption demand by the local inhabitants and Colombia for the piracatinga has created a market for distribution of the Amazon river dolphin carcasses to be used as bait throughout these regions.<ref name="Dolphins"/>{{rp|54–58}}<ref name="Alves 2012"/>

For example, of the 15 dolphin carcasses found in the [[Japurá River]] in 2010–2011 surveys, 73% of the dolphins were killed for bait, disposed of, or abandoned in entangled gillnets.<ref name="Iriarte 2013"/> The data does not fully represent the actual overall number of deaths of the Amazon river dolphins, whether accidental or intentional, because a variety of factors make it extremely complicated to record and medically examine all the carcasses.<ref name="Iriarte 2013"/><ref name="Martin 2004"/><ref name="Crespo 2010b"/> Scavenger species feed upon them and the complexity of the river currents makes it nearly impossible to locate all the carcasses.<ref name="Iriarte 2013"/> More importantly, the local fishermen do not report these deaths out of fear that legal action will be taken against them,<ref name="Iriarte 2013"/> as the Amazon river dolphin and other cetaceans are protected under the Brazilian federal law, prohibiting any takes, harassments, and kills of the species.<ref>{{cite journal|last1=Lodi|first1=L.|last2=Barreto|first2=A.|title=Legal actions taken in Brazil for the conservation of cetaceans|journal=Journal of International Wildlife Law and Policy|year=1998|volume=1|issue=3|pages=403–411|doi=10.1080/13880299809353910}}</ref>

== Conservation ==
{{Expand section|date=January 2024}}

=== International River Dolphin Day ===
The ''Global Declaration for River Dolphins'' was signed by nine countries on 24 October 2023, a date chosen as it is known as the International River Dolphin Day. This pact is intended to promote research and cooperation between countries with river dolphin populations. It is hoped that five further countries will join.<ref>{{cite news |url=https://news.mongabay.com/2024/01/nine-countries-sign-global-pact-to-protect-endangered-river-dolphins/ |title=Nine countries sign global pact to protect endangered river dolphins |author=Astrid Arellano |work=Mongabay |date=15 January 2024 |access-date=20 January 2024}}</ref>

=== Amazon and Orinoco Rivers ===
Marine biologist Fernando Trujillo co-founded the Omacha Foundation in 1993 to protect the pink river dolphins in the [[Amazon River|Amazon]] and [[Orinoco]] Rivers.<ref name=":0"/> Since 2013, Trujillo and his team have been measuring the mercury levels in river dolphins. Mercury, leeched into the river through illegal gold mining processes, is harmful to both dolphins and humans.<ref name=":0">{{Cite web |last=Tomassoni |first=Teresa |date=2025-03-16 |title=One Man's Quest to Protect Pink River Dolphins |url=https://insideclimatenews.org/news/16032025/protecting-amazon-endangered-pink-river-dolphins/ |access-date=2025-03-23 |website=Inside Climate News |language=en-US}}</ref>

==== Climate Change ====
As global temperatures rise, the Amazon has seen record level of drought and river temperatures.<ref name=":0" /> In 2023, within just two months (September–October), 330 [[Amazon river dolphin|river dolphins]] were found dead in the Amazon region due to extreme drought.<ref>{{Cite web |last=prensa |first=Comunicaciones y |date=2024-09-28 |title=Evaluación de la salud de los delfines de río en la Amazonia colombiana en medio de la sequía extrema |url=https://omacha.org/evaluacion-salud-delfines-rio-amazonia-colombiana-sequia-extrema/ |access-date=2025-03-23 |website=Fundación Omacha |language=es}}</ref><ref name=":0" />

=== Captivity ===
[[File:Acuario de Valencia.JPG|thumb|upright|300px|One of two trained [[Amazon river dolphin]] in the world at the [[Acuario de Valencia]], Venezuela]]
A baiji conservation [[dolphinarium]] was established at the Institute of Hydrobiology (IHB) in Wuhan in 1992. This was planned as a backup to any other conservation efforts by producing an area completely protected from any threats, and where the baiji could be easily observed. The site includes an indoor and outdoor holding pool, a water filtration system, food storage and preparation facilities, research labs and a small museum. The aim is to also generate income from tourism which can be put towards the baiji plight. The pools are not very large, only kidney shaped tanks with dimensions of {{convert|82|ft|m|sp=us}} arc {{convert|23|ft|m|sp=us}} width and {{convert|11|ft|m|sp=us}} depth, {{convert|33|ft|m|sp=us}} diameter, {{convert|6.6|ft|m|sp=us}} deep and {{convert|39|ft|m|sp=us}} diameter, {{convert|11|ft|m|sp=us}} deep, and are not capable of holding many baijis at one time.
[[Douglas Adams]] and [[Mark Carwardine]] documented their encounters with the endangered animals on their conservation travels for the BBC programme ''[[Last Chance to See]]''. The book by the same name, published in 1990, included pictures of a captive specimen, a male named Qi Qi (淇淇) that lived in the Wuhan Institute of Hydrobiology [[dolphinarium]] from 1980 to July 14, 2002. Discovered by a fisherman in [[Dongting Lake]], he became the sole resident of the Baiji Dolphinarium (白鱀豚水族馆) beside East Lake. A sexually mature female was captured in late 1995, but died after half a year in 1996 when the Shishou Tian-e-Zhou Baiji Semi-natural Reserve (石首半自然白鱀豚保护区), which had contained only [[finless porpoise]]s since 1990, was flooded.<ref>{{cite web|url=http://english.ihb.cas.cn/rh/rd/center13/201304/t20130418_101038.html|title=Baiji dolphinarium|author=Institute of Hydrobiology|work=Chinese Academy of Sciences|access-date=September 2, 2015|archive-date=February 3, 2022|archive-url=https://web.archive.org/web/20220203134458/http://english.ihb.cas.cn/rh/rd/center13/201304/t20130418_101038.html}}</ref>

The Amazon river dolphin has historically been kept in dolphinariums. Today, only three exist in captivity: one in [[Acuario de Valencia]] in Venezuela, one in Zoologico de Guistochoca in Peru, and one in [[Duisburg Zoo]] in Germany. Several hundred were captured between the 1950s and 1970s, and were distributed in dolphinariums throughout the US, Europe, and Japan. Around 100 went to US dolphinariums, and of that, only 20 survived; the last (named Chuckles) died in [[Pittsburgh Zoo]] in 2002.<ref name="Dolphins"/>{{rp|58–59}}

== Mythology ==
[[File:Ganga Kalighat 1875.jpg|thumb|right|[[Ganga (goddess)|Ganga]] on a river dolphin]]

=== Asia ===
In [[Hindu mythology]], the [[Ganges river dolphin]] is associated with [[Ganga in Hinduism|Ganga]], the deity of the [[Ganges]] river. The dolphin is said to be one of the creatures which heralded the goddess' descent from the heavens, and Ganga's mount, the [[Makara (Hindu mythology)|Makara]], is sometimes depicted as a dolphin.<ref>{{cite book|author=Singh, Vijay |title=The River Goddess|location=London|year=1994|isbn=978-1-85103-195-5}}</ref>

In Chinese mythology, the baiji has many origin stories.
For example, near the mouth of the [[Yangtze]], the [[baiji]] was a princess that had lost her parents and had lived with her stepfather, whom she had longed to get away from. The stepfather wanted to trade her since she would be sold for a great sum of money, but as they were crossing the river to get to the trader, a storm rolled in. The enraged stepfather tried to take her, but she plunged herself into the river, was transformed into a dolphin before she drowned, and swam away from her abusive stepfather, who also fell in and was transformed into a [[finless porpoise|porpoise]].<ref name=turvy/>

In another story, the baiji was the daughter of a general deported from the city of [[Wuhan]] during a war who ran away while her father was in duty. Later, the general met a woman who told him how her father was a general. When he realized that she was his daughter, he threw himself into the river out of shame, and his daughter ran after him and also fell into the river. Before they were drowned, the daughter was transformed into a dolphin and the general into a porpoise.<ref name=turvy>{{cite book|author=Samuel Turvy|title=Witness to Extinction: How we Failed to Save the Yangtze River Dolphin|chapter=The Goddess of the Yangtze|pages=[https://archive.org/details/witnesstoextinct0000turv/page/n20 3]–4|year=2008|publisher=Oxford University Press |isbn=978-0-19-954947-4|id={{ASIN|0199549486|country=uk}}|url=https://archive.org/details/witnesstoextinct0000turv|url-access=registration}}</ref>

=== South America ===
[[Amazon river dolphin]]s, known by the [[Indigenous peoples of the Americas|native]]s as the [[boto]], encantados or toninhas, are very prevalent in the mythology of the native South Americans. They are often characterized in mythology with superior musical ability, seductiveness and love of sex that often results in illegitimate children, and attraction to parties. Despite the fact that the Encante are said to come from a [[utopia]] full of wealth and without pain or death, the encantados crave the pleasures and hardships of human societies.<ref name=Hall>{{cite book|last=Hall|first=Jamie|chapter=Enchanted Dolphins|title=Half Human, Half Animal: Tales of Werewolves and Related Creatures|location=Bloomington, IN|year=2003|pages=55–88|isbn=978-1-4107-5809-5}}</ref>

Transformation into human form is said to be rare, and usually occurs at night. The encantado will often be seen running from a [[festival|festa]], despite protests from the others for it to stay, and can be seen by pursuers as it hurries to the river and reverts to dolphin form. When it is under human form, it wears a hat to hide its [[Blowhole (anatomy)|blowhole]], which does not disappear with the [[shapeshift]].<ref name=Hall/>

Besides the ability to shapeshift into human form, encantados frequently wield other magical abilities, such as controlling storms, hypnotizing humans into doing their will, transforming humans into encantados, and inflicting [[illness]], [[insanity]], and even [[death]]. [[Shamans]] often intervene in these situations.<ref name=Hall/>

[[Kidnapping]] is also a common theme in such [[folklore]]. Encantados are said to be fond of abducting humans with whom they fall in love, children born of their illicit love affairs, or just about anyone near the river who can keep them company, and taking them back to the Encante. The fear of this is so great among people who live near the Amazon River that both children and adults are terrified of going near the water between dusk and dawn, or entering water alone. Some who supposedly have encountered encantados while out in their [[canoe]]s have been said to have gone insane, but the creatures seem to have done little more than follow their boats and nudge them from time to time.<ref name=Hall/>

==References==
{{reflist|30em}}

==Further reading==
* Reeves, Randall R. et al. (2002). ''National Audubon Society Guide to Marine Mammals of the World''. Alfred A. Knopf. 527 pp.

{{Cetacea}}
{{Portal bar|Cetaceans|Mammals}}

[[Category:River dolphins| ]]
[[Category:Extant Oligocene first appearances]]
[[Category:Animals that use echolocation]]
[[Category:Mammal common names]]
[[Category:Polyphyletic groups]]