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″S 43°45′00″E / 23.5666667°S 43.75°E), and into the Bay of Saint-Augustin.
| Onilahy River | |
|---|---|
 Onilahy River estuary | |
 Map of the Onilahy River watershed | |
| Location | |
| Country | Madagascar |
| region | Atsimo-Andrefana, Anosy |
| Cities | Mandrofify, Ambolofoty |
| Physical characteristics | |
| Source | |
| • location | near Betroka |
| Mouth | Bay of Saint-Augustin |
• location | Saint Augustin, Mozambique Channel |
• elevation | 0m |
| Length | 525 km (326 mi) |
| Basin size | 31,600 km2 (12,200 sq mi)[1] |
| Discharge | |
| • location | Near mouth |
| • average | (Period: 1971–2000)183 m3/s (6,500 cu ft/s)[2] |
| Basin features | |
| Protection status | |
| Official name | Zones humides de l'Onilahy |
| Designated | 22 May 2017 |
| Reference no. | 2304[3] |
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]
Geography
editSources 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.
References
edit- ^ Onilahy
- ^ "Madagascar".
- ^ "Zones humides de l'Onilahy". Ramsar Sites Information Service. Retrieved 25 April 2018.
- ^ 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.
- ^ 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.
- ^ 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.