Platanista (Familie Platanistidae) ist eine Gattung der Zahnwale, die in großen Flüssen im Norden des Indischen Subkontinents verbreitet ist. Es werden zwei Arten unterschieden, der eigentliche Gangesdelfin (Platanista gangetica) im Ganges-Brahmaputra-System und der Indusdelfin (Platanista minor) im Indus.[1]
Platanista-Arten haben eine lang ausgezogene und leicht aufwärts gebogene Schnauze. Sie sind zwei bis drei Meter lang, wobei Weibchen im Schnitt etwas größer als Männchen sind und bis zu hundert Kilogramm wiegen. Die Rückenflosse ist klein und unauffällig. In all diesen Merkmalen gleichen die Platanista-Arten dem Amazonasdelfin, obwohl nur eine entfernte Verwandtschaft zu diesem besteht.
Die Körperfarbe ist dunkelgrau; die Unterseite ist etwas heller als die Oberseite. Den Augen fehlt eine Linse, und sie sind verkümmert. Mit den Augen können die Delfine allenfalls noch Helligkeitsunterschiede ausmachen. Die wirkliche Orientierung erfolgt über die Echo-Ortung. Offenbar hat das Leben im schlammigen Wasser den Gesichtssinn verkümmern lassen.
Die Platanista-Arten leben in unterschiedlichen Flusssystemen. Der Gangesdelfin bewohnt das Ganges-Brahmaputra-System im Nordosten Indiens und in Bangladesch. Die andere Art, der Indusdelfin, lebt im Mittellauf des Indus in Zentral-Pakistan. Ihre Verbreitung war einst wahrscheinlich viel größer und umfasste auch zahlreiche Nebenflüsse des Indus.
Platanista-Arten leben für gewöhnlich einzelgängerisch. Sie bekommen ihren Nachwuchs zum Beginn der indischen Trockenzeit. Das einzige Junge ist etwa 70 cm lang und wird ein Jahr gesäugt. Die Nahrung sind Fische und aus dem Bodenschlamm gegrabene wirbellose Organismen.
Ganges- und Indusdelfin galten ursprünglich als eine Art. In den 1970ern setzte sich die Auffassung durch, sie als getrennte Arten zu führen. 1998 kam Dale W. Rice in seinem weithin als Standardwerk akzeptierten Marine Mammals of the World: Systematics and Distribution zu dem Schluss, dass es keine weitreichenden morphologischen Unterschiede gebe, die eine Trennung rechtfertigten. Er vereinte beide wieder als eine Art und führte den Indusdelfin als Unterart des Gangesdelfins. Andere Werke wie Nowak 1999 oder Wilson & Reeder 2005 führen die beiden Populationen hingegen als getrennte Arten.
Die Gangesdelfine vertreten eine eigene Familie der Zahnwale. Mit den anderen Flussdelfinen wie den Amazonas-Flussdelfinen verbinden sie der gemeinsame Lebensraum sowie morphologische Gemeinsamkeiten, die durch konvergente Evolution entstanden sein dürften. Früher wurden die Gangesdelfine manchmal zusammen mit dem Amazonas-, dem La-Plata- und dem Chinesischen Flussdelfin in eine eigene Familie (Platanistidae) oder Überfamilie (Platanistoidea) klassifiziert, dem widersprechen jedoch molekulargenetische Untersuchungen. Heute gelten die Gangesdelfine als einzige Überbleibsel einer einst in mehreren Familien verbreiteten Entwicklungslinie der Wale. Phylogenetisch bilden sie die Schwestergruppe eines gemeinsamen Taxons aus Flussdelfinen und Delfinartigen.
Beide Platanista-Arten sind gefährdet, da sie sich immer wieder in Fischernetzen verfangen, durch Schleusen und Staudämme eingeschränkt und durch Gifteinleitungen in die Flüsse unfruchtbar werden. Zudem werden in manchen Regionen Gangesdelfine gefangen; ihr Fleisch gilt zwar als wertlos, aber ihr Tran gilt als Aphrodisiakum, und das Fleisch wird als Köder beim Angeln nach Welsen verwendet. Beide Arten stehen als stark gefährdet (endangered) auf der Roten Liste der IUCN.
Platanista (Familie Platanistidae) ist eine Gattung der Zahnwale, die in großen Flüssen im Norden des Indischen Subkontinents verbreitet ist. Es werden zwei Arten unterschieden, der eigentliche Gangesdelfin (Platanista gangetica) im Ganges-Brahmaputra-System und der Indusdelfin (Platanista minor) im Indus.
South Asian river dolphins are toothed whales in the genus Platanista, which inhabit fresh water habitats in the northern 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 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 cetaceans with long snouts or rostra, broad flippers, and small dorsal fins. They have several unusual features. Living in murky river waters, their eyes are tiny and lensless. The dolphins rely instead on echolocation for navigation. The skull has large crests over the 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 by the IUCN Red List of mammals. Major threats include dams, barrages, fishing nets, and both chemical and acoustic pollution.
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,[3] a Latin word derived from the Greek "platanistēs", which may be related to the Greek words platē ("oar") or platē ("flat, broad").[4] This name was first given to the Ganges dolphin by Pliny the Elder in Naturalis Historia back in 77 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.[3]
Based on differences in skull and vertebrae structure, blood proteins, and lipids, scientists declared them to be separate species in the 1970s.[5][6] 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.[7][6] A 2014 mitochondrial DNA study found insufficient differences to support their classification as separate species.[6] 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.[3]
South Asian river dolphins are the only surviving members of the family Platanistidae and the superfamily Platanistoidea.[8] They are not closely related to other river dolphins of the families Lipotidae, Pontoporiidae, and Iniidae, which all independently adapted to freshwater habitats.[9] 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:[10][11]
Toothed whales Delphinoidea Belugas, narwhals (Monodontidae)
Porpoises (Phocoenidae)
Oceanic dolphins (Delphinidae)
Beaked whales (Ziphiidae)
South Asian river dolphins (Platanistidae)
Dwarf sperm whales (Kogiidae)
Sperm whales (Physeteridae)
Several fossil species have been classified under Platanistoidea, the earliest of which date back to the late Oligocene (c. 25 million years ago). The number of species peaked around the early Miocene (c. 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.[8]
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.[9] River dolphins likely traveled from the Ganges River basin to the Indus via stream capture within the last five million years. The split between the two species is estimated to have occurred around 550,000 years ago based on mitochondrial DNA.[12]
South Asian river dolphins are stocky with broad, squared-off pectoral fins; elongated, slender rostrums (snouts); and tiny triangular dorsal fins. Their neck joints give them great flexibility.[3][13][14] Unusual among cetaceans, the blowhole is slit-shaped.[14] The finger bones can also be seen through the flippers.[13] South Asian river dolphins possess some features that are "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.[15] 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.[3]
In one study sampling 46 Ganges river dolphins, the maximum length and weight recorded were 267 cm (8.76 ft) and 108 kg (238 lb). For the Indus species, the maximum length and weight were 241 cm (7.91 ft) and 120 kg (260 lb) (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.[3]
South Asian river dolphin skulls have unusual features. The maxilla (fixed upper jawbone) has pneumatic extensions or "crests" on each side which curve around the melon and protrude forward over the rostrum. These likely help them focus their echolocation signals in their riverine environment.[16] The Ganges species also has a protrusion near the frontal suture, which distinguishes it from the Indus species.[3] The teeth of South Asian river dolphins are curved and longer in the front, where they remain exposed when the jaws are closed.[14] 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.[3]
Living in murky waters, South Asian river dolphins are nearly blind, their tiny eyes having flattened corneas and no 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.[17] The ears are adapted to hearing low frequencies, having a short, flattened cochlea with widely spaced spirals.[8]
South Asian river dolphins inhabit the northern waterways of the Indian subcontinent. Ganges river dolphins live in the Ganges, Brahmaputra, Meghna, Karnaphuli, and Sangu rivers and their tributaries. Their range extends from the Himalayan foothills to the Ganges Delta, across the countries of Nepal, India and Bangladesh.[3][14] It is unknown if they are present in Bhutan.[18] 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 300 km (190 mi) southwest of the Ganges Delta.[19] This species has maintained much of its range since the 19th century but has disappeared from some northern and western rivers and waterways.[3]
The Indus river dolphin mainly lives in the Indus River of Pakistan, with three subpopulations between the Chashma, Taunsa, Guddu, and Sukkur barrages. Two other populations exist south of Sukkur and in the Beas River of India.[3][20] 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.[3] The Indus river dolphin is reported to have disappeared between the Jinnah and Chashma barrages after 2001.[20]
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 pools, meanders, and confluences, and around river islands and shoals, which produce relatively stable waters.[19] They can be found in pools over 30 m (98 ft) deep, but usually dwell in shallower water.[14]
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.[21] They swim on their sides when in shallow water.[22] River dolphins generally surface with the rostrum, head, and dorsal fin breaking the water and rarely 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.[23]
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.[14] Living in shallow river environments with acoustic obstacles, these dolphins echolocate using repetitive clicks spaced 10 to 100 milliseconds apart.[24][25] 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.[16] Vocalizations used for communication include bursts and twitterings.[26]
River dolphins feed mainly on fish and shrimp. In one study, around 46% of prey items were found to be bottom-dwelling species, while 31% were near the surface, and 23% occupied the middle of the column. The most frequently taken prey are catfish, barbs, glass perches, spiny eels, gobies, and prawns. When hunting at the surface, dolphins listen for the movements of schooling fish which are then herded with spins, side-swimming, and 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 20 m (66 ft) away. They flush out bottom-dwelling prey by digging around.[22]
Little is known about reproduction in these river dolphins.[14] 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.[15] Calves are born around a year later.[27] 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.[14] Indus river dolphins calves are around 70 cm (28 in) 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.[28] Growth layers in the teeth suggest South Asian river dolphins can live up to 30 years.[29]
As of 2022, the IUCN Red List of mammals lists both South Asian river dolphins as endangered.[18][30] Two assessments in 2014 and 2015 estimated populations of 3,500 for the Ganges river dolphin and 1,500 for the Indus river dolphin.[19][31] The Ganges species appears to be decreasing, while the Indus species may be increasing.[18][30] The habitat of these river dolphins intersects with some of the most densely populated areas, leading to intense competition for water and resources.[19][31][32]
The creation of dams and barrages in the Indus River system have heavily fragmented the range of the Indus river dolphin, leading to a population decline of 80% since the 19th century.[31] Around 50 such structures have been built in the historical range of the Ganges species.[19] Fragmentation of populations makes these dolphins more vulnerable to inbreeding.[32] The heavy extraction of water in these dense populations also puts the dolphins at risk.[19]
River dolphins accumulate high amounts of persistent organic pollutants, pesticides, and heavy metals in their system due to being at the top of their riverine food web.[19][31] Hence, they are seen as bioindicators for the health of river systems.[19] Fisherman compete with these animals for fish of certain sizes.[32] Dolphins captured in fishing nets are usually accidental, but dolphin oil is sought after as a fish lure, and thus fishermen may be motivated to kill caught dolphins.[19] Being nearly blind and relying on echolocation for navigation, river dolphins are also negatively affected by noise pollution from boats.[33]
South Asian river dolphins are protected by law in all the states they inhabit. They can be found in numerous protected areas,[18][30] including ones established specifically for them, such as the Indus Dolphin Reserve in Pakistan and the Vikramshila Gangetic Dolphin Sanctuary in India.[19][31] 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.[34] The Ganges and Indus river dolphins are considered to be the national aquatic animals of India and Pakistan respectively.[35][36]
South Asian river dolphins are toothed whales in the genus Platanista, which inhabit fresh water habitats in the northern 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 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 cetaceans with long snouts or rostra, broad flippers, and small dorsal fins. They have several unusual features. Living in murky river waters, their eyes are tiny and lensless. The dolphins rely instead on echolocation for navigation. The skull has large crests over the 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 by the IUCN Red List of mammals. Major threats include dams, barrages, fishing nets, and both chemical and acoustic pollution.
Platanista est un genre de cétacés qui comprend deux espèces :
Platanista est un genre de cétacés qui comprend deux espèces :
Platanista gangetica (dauphin du Gange ou sousouc) précédemment connu comme Platanista gangetica gangetica Platanista minor (dauphin de l'Indus) précédemment connu comme Platanista gangetica minorSuzu gangesowy[3], suzu[4], delfin gangesowy[4], delfin indyjski[5], susuka[4] (Platanista gangetica) – gatunek ssaka z rodziny suzowatych (Platanistidae) żyjący w wodach Gangesu i Indusu[6].
Takson po raz pierwszy opisany przez Roxburgha w 1801 roku pod nazwą Delphinus gangetica[7]. Jako miejsce typowe autor wskazał Bengal Zachodni w Indiach[7]. Jedyny przedstawiciel rodzaju Platanista – suzu[3], utworzonego przez Waglera w 1830 roku[8].
Wyróżnia się dwa podgatunki[3]:
Według Wilsona i Reedera uznawane za odrębne gatunki[11].
Pysk wyciągnięty na kształt chirurgicznej pincety; w szczęce górnej 26-39, w żuchwie 26-35 par zakrzywionych do tyłu zębów. Zęby przednie są dłuższe niż tylne i wystają z zamkniętego dzioba. Małe oczy, wydatny melon i duża warstwa tkanki tłuszczowej, a wreszcie garb w tylnej części grzbietu sprawiają, że zwierzę ma dość masywny wygląd. Delfin suzu ma giętki kark. Do polowania używa echolokacji. Żyje i poluje w małych stadach.
Suzu gangesowy, suzu, delfin gangesowy, delfin indyjski, susuka (Platanista gangetica) – gatunek ssaka z rodziny suzowatych (Platanistidae) żyjący w wodach Gangesu i Indusu.
Gangesdelfiner (Platanista) är ett släkte i underordningen tandvalar som består av två arter eller en art med två underarter, beroende på taxonomi. Platanista är det enda släktet i familjen Platanistidae.
Arter enligt Mammal Species of the World:[1]
Gangesdelfiner har en långdragen och lite uppåt böjd nos. Kroppslängden ligger mellan 2 och 3 meter. Honor som blir upp till 100 kg tunga är lite större än hannar. Stjärtfenan är liten och inte påfallande. De liknar i flera hänseenden arten Amazondelfin (Inia geoffrensis) men är inte närmare släkt med denne.
Kroppsfärgen är mörkgrå med en något ljusare undersida. Ögonen är rudimentära och saknar lins. Trots allt kan de skilja mellan olika ljusstyrkor. I vattnet orienterar sig gangesdelfiner med eko-lokalisering.
Släktets två arter lever i olika flodsystem. Arten Platanista gangetica finns i floderna Ganges och Brahmaputra samt deras bifloder i nordöstra Indien och Bangladesh. Den andra arten, Platanista minor, förekommer i mellersta delen av floden Indus i Pakistan. Arten hade tidigare ett betydligt större utbredningsområde och levde i flera av Indus' bifloder.
Gangesdelfiner hotas av att de fastnar i fiskenät. Dessutom försämras utbredningsområdets kvalitet genom byggandet av slussar och dammbyggnader samt förorening av vattnet med gifter som gör delfinerna infertila. I vissa regioner fångas dessa delfiner direkt. Köttet används inte som mat utan som fiskbete för malar och tranet nyttjas som afrodisiakum. Bägge arter eller underarter listas av IUCN som stark hotad (endangered).[2]
Gangesdelfiner lever utanför parningstiden ensam. Ungdjuren föds vid början av regionens torrperiod. Ungdjuret är vid födelsen cirka 70 cm lång och honan diar ungefär ett år. Födan utgörs av fiskar och ryggradslösa djur som grävas upp från flodens bottensediment.
De två nämnda arterna räknades ursprungligen till samma art. Under 1970-talet blev åsikten att varje population är en egen art allt vanligare. Populationen från Indus fick då det vetenskapliga namnet Platanista indi. Å andra sidan ansåg Dale W. Rice 1998 i sitt allmänt accepterade verk Marine Mammals of the World: Systematics and Distribution att populationernas morfologiska skillnader inte är tillräcklig stora för att lista de som självständiga arter. Senare auktorer som Nowak 1999 och Wilson & Reeder 2005 redovisar däremot två arter.
Gangesdelfiner räknas som självständig familj i underordningen tandvalar. De har samma habitat som andra floddelfiner och även liknande anatomiska egenskaper som troligen uppkom på grund av konvergent evolution. I vissa äldre systematiker listades Gangesdelfiner tillsammans med Amazondelfin, asiatisk floddelfin och Laplatadelfin till en gemensam familj (Platanistidae) eller överfamilj (Platanistoidea) men molekylärgenetiska undersökningar visade att denna indelning är en motsägelse. Enligt modern kladistik är gangesdelfiner systergruppen till ett gemensamt taxon av överfamiljen Delphinoidea (vitvalar, tumlare och delfiner) och de andra floddelfinerna.
Gangesdelfiner (Platanista) är ett släkte i underordningen tandvalar som består av två arter eller en art med två underarter, beroende på taxonomi. Platanista är det enda släktet i familjen Platanistidae.
Arter enligt Mammal Species of the World:
Platanista gangetica Platanista minor, listas av IUCN som underartGanj nehir yunusu (Platanista gangetica gangetica) ve İndus nehir yunusu (Platanista gangetica minor) Bangladeş, Hindistan ve Pakistan'da bulunan tatlısu ya da nehir yunusları üstfamilyasının iki alttürüdür. 1970'lerden itibaren iki ayrı tür olarak nitelendirilmektedirler. Ganj nehri yunusu çoğunlukla Hindistan'da Ganj Nehri ve kollarında, İndus nehir yunusu da Pakistan'da İndus Nehri'nde bulunur. Ancak 1998 yılında balinalar üzerine yapılan bir taksonomi çalışması sonucunda bu iki yunus tekrar tek tür olarak listelenmiştir. Bu türün adı Ganj ve İndus nehir yunusu ya da daha genel adıyla Hint nehir yunusudur ancak bu iki isim de çok fazla yaygın değildir.
İlk olarak 1801'de Roxburgh tarafından isimlendirilen Ganj ve İndus nehir yunusları 1970'lere kadar tek tür olarak değerlendiriliyordu. Ancak bu tarihte, Hindistan'da Ganj Nehri'nde yaşayan popülasyon ile Pakistan'da İndus Nehri'nde yaşayan popülasyonun birbirleri ile çiftleşmediği açıkça ortaya çıkmıştır. Kafatası yapısındaki farklılık nedeniyle biliminsanları bu iki popülasyonun ayrı türler olduğunu açıkladı. Ancak Rice 1998 yılında yaptığı ve artık standart hâline gelen balina sınıflandırma çalışmasında iki ayrı türü gerektirecek kadar morfolojik farklılıklar olmadığını buldu.[1] Dolayısıyla Platanista cinsinde yalnızca bir tür yer almıştır. Nehir yunusları da dört tür olarak her biri kendi familyası ve cinsinde sınıflandırılmıştır.
Ganj ve İndus nehir yunusları görünüş itibarıyla esasen hemen hemen aynıdır. Tüm nehir yunuslarının karakteristik özelliği olan uzun ve sivri bir ağza sahiptir. Ağız kapalıyken bile alt ve üst çenede bulunan diş dizileri görünür. Ağız uca doğru gittikçe kalınlaşır. Bu tür yunusların göz merceği yoktur. Işığın yoğunluğunu ve geldiği yönü hissetseler bile bu yunuslar kördür. Yankı ile yönbularak hareket eder ve avlanırlar. Kahverengimsi bir renge sahip olan gövde ortada kalınlaşır. Bu türde sırt yüzgeci yerinde küçük üçgen bir şişlik bulunur. Yan yüzgeçler ve kuyruk erkeklerde 2-2,2 metre ve dişilerde 2,4-2,6 metre olan gövde boyutlarına göre ince ve geniştir. Yaşam süreleri ve yaşamları ile ilgili diğer noktalar bilinmemektedir.
Bu tür yunuslar karides ve nehir yatağına yakın yerleri tercih eden küçük balıklarla beslenir. Genellikle tek olarak görülen yunusların, popülsayonları daha büyük olduğu geçmiş zamanlarda grup olarak dolaştıkları bilinmektedir.
Ganj alttürü Ganj Nehri'nde olduğu kadar, Hindistan, Bangladeş, Nepal ve Bhutan'ın Brahmaputra, Meghna, Karnaphuli ve Sangu nehir sistemlerinde de bulunur. Görece yüksek popülasyon yoğunluğuna Hindistan'ın Vikramshila Ganj Yunusu Korunağı yakınında ve güney Bangladeş'te Sangu Nehri'nde rastlanmıştır. Çok az sayıda (20 kadar) yunus Nepal'in Karnali Nehri'nde bulunur. Toplam popülasyon bilinmese de birkaç bin kadar olduğu sanılmaktadır.
İndus alttürü asıl olarak Pakistan'da İndus Nehri'ndedir. 19. yüzyılda yaşama alanı İndus Nehri'nin kolları olan Sutlej, Ravi, Chenab ve Jhelum nehirlerini de kapsayacak şekilde bugünkünün yaklaşık beş katıydı. En büyük popülasyon yoğunluğu Sind Eyaleti'ndedir.
WWF-Pakistan tarafından 2001 yılında tamamlanan kapsamlı sayıma göre günümüzde yaşayan 1.100 birey bulunmaktadır.
Her iki alttürde doğal yaşam alanlarını oluşturan nehir sistemlerinin insanlar tarafından kullanılmasından oldukça olumsuz şekilde etkilenmişlerdir. Balık ağlarına takılma yerli popülasyon sayısının azalmasında önemli derecede etkilidir. Her yıl yakalanan bazı bireylerin et ve yağları eklem ve romatizma ağrılarına karşı merhem, afrodizyak ve yayınbalığı için yem olarak kullanılır. Sulama nedeniyle her iki alttürün de yaşam alanlarında su düzeyleri azalmıştır. Sanayide ve ziraatte kullanılan kimyasallarla zehirlenen su da popülasyonun azalmasında etkili olmuştur. Belki de en önemli etki birçok nehir boyunca 50 kadar baraj yapıldıktan sonra popülasyonların birbirinden ayrılarak üreyebilecekleri çok küçük bir gen havuzu bırakılmasıdır. İndus yunuslarının korundukları takdirde uzun süre yaşayabilecekleri sanılan üç ayrı alt popülasyonu bulunmaktadır.
Her iki alttür de IUCN tarafından yayımlanan "Kırmızı Liste"de yer almıştır.[2]
Ganj nehir yunusu (Platanista gangetica gangetica) ve İndus nehir yunusu (Platanista gangetica minor) Bangladeş, Hindistan ve Pakistan'da bulunan tatlısu ya da nehir yunusları üstfamilyasının iki alttürüdür. 1970'lerden itibaren iki ayrı tür olarak nitelendirilmektedirler. Ganj nehri yunusu çoğunlukla Hindistan'da Ganj Nehri ve kollarında, İndus nehir yunusu da Pakistan'da İndus Nehri'nde bulunur. Ancak 1998 yılında balinalar üzerine yapılan bir taksonomi çalışması sonucunda bu iki yunus tekrar tek tür olarak listelenmiştir. Bu türün adı Ganj ve İndus nehir yunusu ya da daha genel adıyla Hint nehir yunusudur ancak bu iki isim de çok fazla yaygın değildir.
恆河豚又名恆河江豚是生活於印度、孟加拉、尼泊爾與巴基斯坦的淡水豚,分成兩種亞種:印度河亞種(Platanista gangetica minor)與恆河亞種(Platanista gangetica gangetica)。恆河亞種生活在恆河與布拉馬普特拉河及它們位於印度、孟加拉與尼泊爾境內的支流中,而印度河亞種則只棲息在巴基斯坦的印度河中。從1970年代直到1998年為止,牠們被當成是兩個不同的種。不過在1998年,棲息於恆河與印度河的恆河豚族群被重新分類為恆河豚的兩個亞種。
恆河豚在1801年時分別由兩位不同的作者Lebeck與Roxburgh所描述,而且原先並不清楚牠們應該歸屬於哪一類[1]。一直到1970年代,恆河亞種與印度河亞種一直被認為是同一個種。這兩個族群的分布範圍並沒有重疊,而且在幾千或幾百年內沒有互相雜交過。所以根據牠們頭骨結構、脊椎骨與脂質構造的不同,科學家於是在1970年代早期宣布這兩個族群是兩個不同的種[2]。之前的研究結果是具有爭論的,直到後來使用了現代技術(如分子序列)才解決這個分類上的難題,所以在1998年時回復到1970年以前的分類方式,認為恆河與印度河的恆河豚族群是兩個「亞種」,而不是兩個「種」,因此現在將恆河豚分類成印度河亞種與恆河亞種[3]。
恆河亞種與印度河亞種實際上是相當類似的,牠們擁有所有河豚共有的長嘴喙。即使在嘴巴沒有張開的情況下,仍然可以看見明顯的牙齒生長在上下顎。年幼的恆河豚牙齒約有一英吋長,而且是窄且彎曲的。但隨著年齡增長,牙齒將變成平坦且方正的。恆河豚的眼睛沒有晶狀體,所以牠們實際上等同於失明,雖然牠們可以感覺到光的強度與方向。導航與覓食則是使用回聲定位。恆河豚的身體中間部分是咖啡色的,牠們只擁有三角型的小型背鰭,而前肢及尾鰭與身體比起來是較大的。雄性的恆河豚身長約2-2.2公尺,雌性的恆河豚則為2.4-2.6公尺。
目前已知紀錄上最老恆河豚是一隻28歲的雄性恆河豚,身長為199公分[4]。成年的雌性恆河豚的體型比雄性恆河豚還要大。兩性異形顯示在雌性恆河豚身長達到150公分後,雖然當時雄性恆河豚的嘴喙停止生長了,雌性恆河豚的嘴喙仍然會繼續生長,最後達到約20公分長。幼豚可以在1月到5月間觀察到,而且不會停留在雌性恆河豚身邊超過幾個月。恆河豚的懷孕期約9至10個月。
恆河豚以魚及蝦作為主食,包括鯉魚與鯰魚。恆河豚被觀察到時通常是單獨行動或是以鬆散的群體來行動,牠們並不會組成嚴謹而且有明顯互動的集團。
印度河亞種分布在印度河流域及印度、尼泊爾、孟加拉與不丹境內的梅克納河(Meghna)、布拉馬普特拉河、戈爾諾普利河(Karnaphuli)與Sangu河流域。恆河豚在印度的Vikramshila恆河豚庇護所附近與孟加拉南部的Sangu河流域有相對比較高的數量分布。只有非常少的個體(可能只有20隻)生活在尼泊爾的卡克拉河(Ghaghara)中。印度河亞種的總數量目前是未知的,不過可以確定的是至少有幾百隻,也許多達上千隻。
昌巴爾河(Chambal)發源於印度西部,然後在安拉阿巴德(Allahabad)注入印度河。Singh與Sharma (1985)[5]估計在1983年至1985年(Fig.1)之間至少有45隻恆河豚生活在Batesura與Pachhnada之間的昌巴爾河中。觀測密度約每6.5公里有一隻成年的恆河豚。
印度河亞種棲息在巴基斯坦的印度河流域。19世紀時,在印度河的河口到喜馬拉雅山麓丘陵之間及象泉河、拉維河、傑納布河與傑赫勒姆河(Jhelum)這些支流發現牠們的蹤跡。目前印度河亞種只棲息在印度河長約1,000公里的河道中,因為灌溉設施而被分成5個族群。大約有99%的數量出現在690公里的河道裡,這顯示在1870年代以來印度河亞種的分布範圍縮小了80%。
一次由世界自然基金會-巴基斯坦對印度河亞種所作的廣泛的數量統計在2001完成,認為目前約有1,100隻印度河亞種[6]。觀察到恆河豚在下游的族群數量與目擊率有明顯的增加。目前有3個巨大的族群,分別位於恰希瑪(Chashma)與陶沙(Taunsa)水壩之間(84隻,密度0.28隻/km)、陶沙(Taunsa)與Guddu水壩之間(259隻,密度0.74隻/km)及Guddu與蘇庫爾(Sukkur)水壩之間(602隻,密度3.60隻/km)。
印度半島的人類在河川系統的使用上,對於恆河豚的兩個亞種都有非常不利的影響。魚網會導致牠們被纏住,造成局部地區的數量嚴重的減少。每年仍然有一些恆河豚被獵捕,而牠們的油與肉被當作塗敷的藥劑、春藥與捕捉鯰魚的餌。灌慨也降低了恆河豚棲息範圍內河流的水位。工業與農業用的化學藥品排放到水中的毒素可能也造成恆河豚數量的下滑。最重要的問題可能是在許多河流中總共建造了超過50座水壩,造成恆河豚族群被分離與基因庫的減少,因為能交配的數量減少了。目前有3個印度河亞種的族群,如果保育得當被認為可以長期的倖存下去。
印度河亞種與恆河亞種被世界自然保護聯盟的世界自然保護聯盟瀕危物種紅色名錄列入瀕危等級[7]。對於棲息在國家Chambal保育所的恆河豚而言,立即的危險是水位降低與攔沙壩的出現使得河流被切割成較小的部分[5]。
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(帮助) 恆河豚又名恆河江豚是生活於印度、孟加拉、尼泊爾與巴基斯坦的淡水豚,分成兩種亞種:印度河亞種(Platanista gangetica minor)與恆河亞種(Platanista gangetica gangetica)。恆河亞種生活在恆河與布拉馬普特拉河及它們位於印度、孟加拉與尼泊爾境內的支流中,而印度河亞種則只棲息在巴基斯坦的印度河中。從1970年代直到1998年為止,牠們被當成是兩個不同的種。不過在1998年,棲息於恆河與印度河的恆河豚族群被重新分類為恆河豚的兩個亞種。
Delphinus gangetica Roxburgh, 1801
Platanista minor Owen, 1852
Platanista gangeticaは、偶蹄目(鯨偶蹄目とする説もあり)ガンジスカワイルカ科ガンジスカワイルカ属に分類される鯨類。本種のみでガンジスカワイルカ科ガンジスカワイルカ属を構成する。
カワイルカ科 (Platanistidae) はクジラ目に属する科の一つ。マイルカ科などよりも初期に分岐したグループで、祖先的な特徴を持つ。淡水から汽水域に生息する。カワイルカ属に属するのはインドカワイルカ、ガンジスカワイルカ、インダスカワイルカである。分類についての詳細は本文の「分類学」を参照されたい。スースーとも呼ばれる[要検証 – ノート]。
ガンジスカワイルカはガンジス川だけでなく、インド、バングラデシュ、ネパール、ブータンを流れるブラマプトラ川、Meghna川、Karnaphuli川、Sangu川に棲息する。 インドのVikramshila保護区 (Vikramshila Gangetic Dolphin Sanctuary) や南バングラデシュのSangu川における生息数は比較的多い。 ネパールのKarnali川にはごくわずかの個体(おそらく20頭程度)が棲息する。 全生息数は不明であるが、少なくとも数百頭、おそらく数千頭規模だと考えられている。(「人間との関り」も参照)
インダスカワイルカは主にパキスタンのインダス川に棲息する。 19世紀における生息域は現在よりも約5倍も広く、インダス川の支流であるSutlej川、Ravi川、Chenab川、Jhelum川にも生息していた。 シンド州 (Sindh Province) における生息数が最も多い。 WWFパキスタンが行った2001年の調査によると、インダスカワイルカの全生息数はおよそ1,100頭に過ぎない。
他のカワイルカと同じく長く尖った口吻を有する。 口を閉じた状態でも、上下の顎の歯が露出している。 口吻は先端の方が太い。 眼には水晶体はなく、光の強さや方向がわかる程度で、ほぼ盲目に近い。 移動や食物探索は反響定位(エコーロケーション)を用いて行う。 褐色系の体色を有し、身体の中央部は大きい。 背びれはなく、三角形の小さな隆起があるだけである。 胸びれや尾びれは細く、体長と比較すると長い。 体長は雄が2mから2.2m、雌が2.4mから2.6mである。
ガンジスカワイルカP. gangeticaとインダスカワイルカP. minorの2種とする説もあった[7]。一方でこれらは外観では区別できず、内部形態でも個体単位では区別ができないとして1種にまとめ2亜種とする説もある[7]。
元々は1801年にRoxburghによって、インドカワイルカ(以下の文中にも登場する名称だが同様に)[要出典] (P. gangetica, Ganges and Indus River Dolphin) として一つの種として分類された。
ところが、1970年代になって、インドカワイルカの生息域はインドのガンジス川とパキスタンのインダス川に完全に分かれており、長い間、交雑していないことがわかった。 頭蓋骨の特徴などを調べた結果、別の種であるとして分類された。 すなわち、ガンジスカワイルカ (P. gangetica, Ganges River Dolphin) とインダスカワイルカ (P. minor, Indus River Dolphin) である。
しかし、1998年、Riceはガンジスカワイルカとインダスカワイルカの形態的な差異は別の種として分類するには不十分であるとした[Rice98]。 このRiceの分類に従えば、種としてはインドカワイルカ(P. gangetica。英名はGanges and Indus River Dolphin あるいは Indian River Dolphin)1種のみが存在し、亜種としてガンジスカワイルカ (P. g. gangetica, Ganges River Dolphin) とインダスカワイルカ (P. g. minor, Indus River Dolphin) に分類される。 現在では、このRiceによる分類法に従うことが多い。
Riceによる分類[Rice98](インドカワイルカ1種のみとする分類法) カワイルカ科 Platanistidae
Rice以前の一般的な分類(ガンジスカワイルカとインダスカワイルカの2種とする分類法) カワイルカ科 Platanistidae
寿命などは不明である。
川底近くに棲息するエビや小魚を食べる。 現在では単独で行動する様子が観察されることが多いが、以前の個体数が多かった頃には群を成しての行動が観察されており、本来は数頭で群を成して行動するものと考えられている。
1975年のワシントン条約発効時からワシントン条約附属書Iに掲載され、1981年からはガンジスカワイルカ属単位でワシントン条約附属書Iに掲載されている[2]。
両亜種とも、棲息流域の人間の行動による多大な悪影響を被ってきた。
個体数の壊滅的な減少の原因の一つは漁網による混獲である。 脂や肉を塗り薬、性欲増進剤、ナマズの餌などとして使用するための捕獲は、現在でも行われている。 灌漑が原因となって、生息域における水位の低下も発生している。 工業排水に含まれる有害物質の排出や、農薬の河川への流出などによる水質悪化も個体数減少の原因となっている。 個体数激減の最も大きな原因は、棲息流域に建設された50基以上のダムだろうと考えられている。 ダムはカワイルカの生息域を完全に分断してしまう。 繁殖に関る個体数が減ることにより遺伝子の攪拌が減少し、生物としての力の低下が起こってしまう。
インダスカワイルカについては、保護が適切であるならば棲息し続けることが可能であろうと考えられている集団は三つ存在する。
ガンジスカワイルカ、インダスカワイルカともに、スースーと呼ばれることがある。 英語ではBlind River Dolphin、Side-swimming Dolphin、 Susu、Bhulanと言った別名がある。
ガンジスカワイルカの英語での別名としては、Gangetic Dolphin、Ganges Susuがある。
インダスカワイルカの英語での別名としては、Bhulan、Indus Dolphin、Indus Susuがある。
Platanista gangeticaは、偶蹄目(鯨偶蹄目とする説もあり)ガンジスカワイルカ科ガンジスカワイルカ属に分類される鯨類。本種のみでガンジスカワイルカ科ガンジスカワイルカ属を構成する。
カワイルカ科 (Platanistidae) はクジラ目に属する科の一つ。マイルカ科などよりも初期に分岐したグループで、祖先的な特徴を持つ。淡水から汽水域に生息する。カワイルカ属に属するのはインドカワイルカ、ガンジスカワイルカ、インダスカワイルカである。分類についての詳細は本文の「」を参照されたい。スースーとも呼ばれる[要検証 – ノート]。