Onilahy River

Last updated
Onilahy River
JNB-MRU 22.08.2009 13-16-31.jpg
Onilahy River estuary
Onilahy watershed.png
Map of the Onilahy River watershed
Location
Country Madagascar
region Atsimo-Andrefana, Anosy
Cities Mandrofify, Ambolofoty
Physical characteristics
Source 
  locationnear Betroka
Mouth Bay of Saint-Augustin
  location
Saint Augustin, Mozambique Channel
  elevation
0m
Length525 km (326 mi)
Basin size31,600 km2 (12,200 sq mi) [1]
Discharge 
  locationNear mouth
  average(Period: 1971–2000)183 m3/s (6,500 cu ft/s) [2]
Basin features
Protection status
Official nameZones humides de l'Onilahy
Designated22 May 2017
Reference no.2304 [3]

Onilahy is a river in Atsimo-Andrefana and Anosy (Toliara Province), southern Madagascar. It flows down from the hills near Betroka to the Mozambique Channel. It empties at St. Augustin ( 23°34′00″S43°45′00″E / 23.5666667°S 43.75°E / -23.5666667; 43.75 ), and into the Bay of Saint-Augustin.

Two species of cichlids are endemic to the river basin, but Ptychochromis onilahy is probably already extinct [4] and the remaining range of Ptychochromoides betsileanus covers less than 10 square kilometres (3.9 sq mi). [5] [6]

Onilahy Bassin Onilahy Basin OSM.png
Onilahy Bassin

Geography

Sources of the Onilahy river are near Beadabo. It flows through Ankilimary, to Benenitra, Ehara, Bezaha and Antanimena. It is crossed by the RN 10 near Tameantsoa. The mouth of the Onilahy river is situated in the Indian Ocean at Saint Augustin, Madagascar, 35 km south of Toliara (Tuléar).

Its main affluentes from its south are Sakamena river, Evasy River, Ianapera River, Isoanala river and the Ihazofotsy River. From the north these are Sakondry, Taheza, Sakamare and the Imatoto rivers.

Related Research Articles

<span class="mw-page-title-main">Fauna of Madagascar</span>

The fauna of Madagascar is a part of the wildlife of Madagascar.

<i>Delonix pumila</i> Species of legume

Delonix pumila is a species of flowering plant in the family Fabaceae. It is endemic to Madagascar.

Paretroplus nourissati, the lamena, is a species of cichlid from the vicinity of the confluence of the Amboaboa and Mangarahara Rivers near Mandritsara in northern Madagascar. This relatively elongate Paretroplus reaches about 16 centimetres (6.3 in) in length, and is closely related to P. lamenabe and P.tsimoly. P. nourissati is threatened by habitat loss and invasive species.

Paretroplus gymnopreopercularis is a species of cichlid from the vicinity of the confluence of the Amboaboa and Mangarahara Rivers near Mandritsara in northern Madagascar. Until its official scientific description in 2008, it was temporarily known as the Paretroplus nov. sp. "sofia". It is endangered because of habitat degradation, overfishing and invasive species. Following the construction of a dam on the Mangarahara River, surveys have failed to relocate P. gymnopreopercularis in this river.

<i>Ptychochromis grandidieri</i> Species of fish

Ptychochromis grandidieri is a species of fish in the family Cichlidae endemic to river basins along a large part of the eastern coast of Madagascar, although it has been recorded as far as 100 km (62 mi) inland. Uniquely in the genus Ptychochromis, this species also occurs in brackish water. It reaches 35cm in standard length. It shares a large part of its range with a cichlid from another genus, Paretroplus polyactis. The specific name honours Alfred Grandidier (1836-1921), the French naturalist and explorer who, with Henri Joseph Léon Humblot (1852-1914), collected the type.

<i>Ptychochromis</i> Genus of fishes

Ptychochromis is a genus of cichlids endemic to rivers and lakes in Madagascar. One species can also be seen in brackish water. Most species in this genus are threatened, and P. onilahy is probably extinct. Most reach a length of 15 to 20 cm, but P. insolitus reaches 25 cm (10 in), while P. grandidieri and P. oligacanthus reach 35 cm (14 in) and 20 cm (8 in) respectively. The largest species was P. onilahy which may have reached as much as 45 cm (18 in) if reports of fishermen are to be believed.

Ptychochromis inornatus is an endangered species of cichlid endemic to the Ankofia River basin and its tributaries in the eastern part of the Mahajanga Province in Madagascar. It is threatened by habitat loss. It reaches 12.2 cm (4.8 in) in standard length.

<i>Ptychochromis oligacanthus</i> Species of fish

Ptychochromis oligacanthus is a species of cichlid endemic in fresh water habitats in the western part of the Antsiranana Province in Madagascar. The population on the island of Nosy Be appears to be stable, but the mainland populations are threatened by habitat loss. It reaches a length of 25 centimetres (9.8 in) TL.

Ptychochromis loisellei is a species of cichlid from the Mahanara River basin north of Sambava in northeastern Madagascar. It remains common within its small range, but it is threatened by habitat loss and introduced species. It reaches about 11.9 centimetres (4.7 in). The similar named Paretroplus loisellei is also restricted to the Mahanara River basin. The specific name honours Paul V. Loiselle, Emeritus Curator of Freshwater Fishes at the New York Aquarium and a researcher in, and campaigner for the conservation of, the freshwater fish of Madagascar.

Ptychochromis curvidens is an endangered species of fish in the cichlid family. It is endemic to a few rivers that flow west from Montagne d'Ambre in far northern Madagascar. It is threatened by habitat loss and introduced species. It reaches about 14.7 cm (5.8 in) in standard length.

Ptychochromis onilahy is a species of cichlid endemic to the Onilahy River in southwestern Madagascar. Despite several recent visits to the region, this species has not been recorded since 1962 when the only known five specimens were collected. It is listed as extinct by the IUCN, but the Onilahy River system is large, and there is a small chance remnant populations exist in remote regions. This species can reach a length of 8.6 centimetres (3.4 in) SL.

<span class="mw-page-title-main">Trondo mainty</span> Species of fish

The trondo mainty is a critically endangered species of cichlid endemic to the Onilahy River Basin in southwestern Madagascar. Its remaining range covers less than 10 km2 (3.9 sq mi) and it is highly threatened by habitat loss, fishing, and competition with/predation by introduced species. Another cichlid from the same basin, Ptychochromis onilahy, is probably already extinct. The trondo mainty reaches a standard length (SL) of 24 cm (9.4 in).

<i>Ptychochromoides</i> Genus of fish in Madagascar

Ptychochromoides is a genus of cichlids endemic to Madagascar. Of the three described species, two are critically endangered and one was considered extinct until rediscovered in late 2010.

Katria is a genus of freshwater fish in the cichlid family. It contains the single species Katria katria, a vulnerable species from the Mangoro and Nosivolo Rivers in east-central Madagascar, that was formerly included in the genus Ptychochromoides. The only other monotypic cichlid genus in Madagascar is Oxylapia, and it is restricted to the same region as Katria. In 2010, the Nosivolo River was designated as a Ramsar Site. The Katria reaches about 13 centimetres (5.1 in) in length.

Sauvagella robusta is a small species of fish in the family Clupeidae. It is endemic to the Amboaboa and Mangarahara River Basins in northern Madagascar. This relatively slender fish reaches a length of 6.8 cm (2.7 in), and is overall pale yellowish with silvery on the lower parts. Its current conservation status is unclear, but the cichlid Ptychochromis insolitus, which is highly threatened from habitat loss, is native to the same region. Sauvagella robusta is known to survive at least in Lake Tseny.

<span class="mw-page-title-main">Saint Augustin, Madagascar</span> Place in Toliara, Madagascar

Saint Augustin is a rural municipality in Madagascar. It belongs to the district of Toliara II, which is a part of Atsimo-Andrefana Region. The population of the commune was estimated to be approximately 15,000 in 2001 commune census. The mouth of the Onilahy River is near the town.

<i>Ptychochromis insolitus</i> Species of fish

Ptychochromis insolitus, also known as the Mangarahara cichlid or joba mena, is a species of cichlid endemic to certain river systems in northern Madagascar. This critically endangered fish is threatened by habitat loss and competition from introduced species; after the last-known female was killed during a breeding attempt, its conservation received significant international attention as London Zoo launched a media campaign to identify any remaining individuals. A remnant population was discovered by aquaculture entrepreneur Guy Tam Hyock in 2013, and breeding programs in Madagascar and at Toronto Zoo have resulted in thousands of successful hatchlings.

Ptychochromis makira is a species of cichlid only known from the Antainambalana River in the northernmost part of the Toamasina Province in Madagascar. It is threatened by habitat loss and overfishing, and has suffered a severe decline in recent years. It reaches a length of 14.6 centimetres (5.7 in) SL.

Ptychochromis ernestmagnusi is a species of fish cichlid only known from the Mananara du Nord River in northeastern Madagascar, but it is probably more widespread in that region. If so, it likely occurs in the Mananara-Nord Biosphere Reserve, which would give it a level of protection. It can reach 14.7 cm (5.8 in) in standard length.

Paretroplus loisellei is a vulnerable species of cichlid fish from the Mahanara River basin north of Sambava in northeastern Madagascar. Until its scientific description in 2011, this population was usually referred to as Paretroplus sp. nov. "Ventitry" or included in P. damii, which it resembles. It reaches about 15 centimetres (5.9 in) in length, and is threatened by habitat loss and introduced species. The similar named Ptychochromis loisellei is also restricted to the Mahanara River basin. The specific name honours Paul V. Loiselle, Emeritus Curator of Freshwater Fishes at the New York Aquarium and a researcher in, and campaigner for the conservation of, the freshwater fish of Madagascar.

References

  1. Onilahy
  2. "Madagascar".
  3. "Zones humides de l'Onilahy". Ramsar Sites Information Service. Retrieved 25 April 2018.
  4. Stiassny, M., and Sparks, J. S. (2006). Phylogeny and Taxonomic Revision of the Endemic Malagasy Genus Ptychochromis (Teleostei: Cichlidae), with the Description of Five New Species and a Diagnosis for Katria, New Genus. American Museum Novitates 3535.
  5. Ravelomanana, T.; Sparks, J.S. (2020). "Ptychochromoides betsileanus". IUCN Red List of Threatened Species . 2020: e.T18832A177066640. doi: 10.2305/IUCN.UK.2020-3.RLTS.T18832A177066640.en . Retrieved 12 November 2021.
  6. Walaszczyk, I.; Marcinowski, R.; Praszkier, T.; Dembicz, K.; Bieńkowska, M. (August 2004). "Biogeographical and stratigraphical significance of the latest Turonian and Early Coniacian inoceramid/ammonite succession of the Manasoa section on the Onilahy River, south-west Madagascar". Cretaceous Research. 25 (4): 543–576. doi:10.1016/j.cretres.2004.05.001. ISSN   0195-6671.