Lake Alaotra
Encyclopedia
Lake Alaotra is the largest lake
in Madagascar
, located in Toamasina Province
, in the northern central plateau. Its basin is composed of shallow freshwater lakes and marshes surrounded by areas of dense vegetation. It forms the center of the island's most important rice-growing region. It is a rich habitat for wildlife, including some rare and endangered species, as well as an important fishing ground. Lake Alaotra and its surrounding wetland
s cover 7223 square kilometres (2,788.8 sq mi) , and include a range of habitats, including open water, reedbeds, marshes, and rice
paddies. The lake itself covers 900 square kilometres (347.5 sq mi) . Lake Alaotra was declared a wetland of international importance
under the international Ramsar Convention
on February 2, 2003.
The Longfin tilapia (Oreochromis macrochir) was introduced into Lake Alaotra from the mainland in 1954, and proliferated quickly.
By 1957 it provided 46% of the catch, perhaps because it was moving into an empty ecological niche as a phytophagous species.
The fertile plain surrounding lake Lake Alaotra is Madagascar's most important rice-producing region. The hills surrounding the lake were formerly forested, but have mostly been cleared for farmland in past decades. Severe erosion
on these vulnerable hill slopes has caused considerable sedimentation
of the lake, which is fast disappearing; the lake is now only 60 centimetres (23.6 in) deep during the dry season. Pressure to create more rice fields has also led locals to burn the reedbeds surrounding the lake. These reedbeds provide the sole habitat of the endemic
Alaotra Gentle Lemur
(Hapalemur griseus alaotrensis). The Alaotra Gentle Lemur is now limited to only 220 square kilometres (84.9 sq mi) of remaining reedbeds, and in recent years the lemur population rapidly declined by 60%, from approximately 7,500 individuals in 1994 to 3,000 in 2001, mostly from habitat loss, but also from hunting by local villagers.
The lake is also an important but increasingly threatened habitat for waterbirds, including the endangered Meller's Duck
(Anas melleri). Two waterbird species were endemic to northern Madagascar, the Madagascar Pochard
(Aythya innotata) and the Alaotra Grebe
(Tachybaptus rufolavatus. The Madagascar Pochard is now critically endangered and no longer found on the lake itself, although very small numbers exist elsewhere. The Alaotra Grebe was declared extinct in 2010. In earlier times, Lake Alaotra was where the largest numbers lived, the near-flightless grebe may never have occurred elsewhere except in the immediate area of the lake.
The Ambato River provides the Lake with water and also drains it. After 381 km the river flows into the Indian Ocean
.
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
in Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
, located in Toamasina Province
Toamasina Province
Toamasina is a former province of Madagascar with an area of 71,911 km². It had a population of 2,855,600 . Its capital was Toamasina, the most important seaport of the country....
, in the northern central plateau. Its basin is composed of shallow freshwater lakes and marshes surrounded by areas of dense vegetation. It forms the center of the island's most important rice-growing region. It is a rich habitat for wildlife, including some rare and endangered species, as well as an important fishing ground. Lake Alaotra and its surrounding wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
s cover 7223 square kilometres (2,788.8 sq mi) , and include a range of habitats, including open water, reedbeds, marshes, and rice
Rice
Rice is the seed of the monocot plants Oryza sativa or Oryza glaberrima . As a cereal grain, it is the most important staple food for a large part of the world's human population, especially in East Asia, Southeast Asia, South Asia, the Middle East, and the West Indies...
paddies. The lake itself covers 900 square kilometres (347.5 sq mi) . Lake Alaotra was declared a wetland of international importance
Ramsar list of wetlands of international importance
This is the list of wetlands of international importance as defined by the Ramsar Convention for the conservation and sustainable utilization of wetlands, recognizing the fundamental ecological functions of wetlands and their economic, cultural, scientific, and recreational value.The Convention...
under the international Ramsar Convention
Ramsar Convention
The Ramsar Convention is an international treaty for the conservation and sustainable utilization of wetlands, i.e., to stem the progressive encroachment on and loss of wetlands now and in the future, recognizing the fundamental ecological functions of wetlands and their economic, cultural,...
on February 2, 2003.
The Longfin tilapia (Oreochromis macrochir) was introduced into Lake Alaotra from the mainland in 1954, and proliferated quickly.
By 1957 it provided 46% of the catch, perhaps because it was moving into an empty ecological niche as a phytophagous species.
The fertile plain surrounding lake Lake Alaotra is Madagascar's most important rice-producing region. The hills surrounding the lake were formerly forested, but have mostly been cleared for farmland in past decades. Severe erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
on these vulnerable hill slopes has caused considerable sedimentation
Sedimentation
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...
of the lake, which is fast disappearing; the lake is now only 60 centimetres (23.6 in) deep during the dry season. Pressure to create more rice fields has also led locals to burn the reedbeds surrounding the lake. These reedbeds provide the sole habitat of the endemic
Endemic (ecology)
Endemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...
Alaotra Gentle Lemur
Lac Alaotra Gentle Lemur
The Lac Alaotra bamboo lemur , also known as the Lac Alaotra gentle lemur, Alaotran bamboo lemur, Alaotran gentle lemur, or locally as the , is a bamboo lemur. It is endemic to the reed beds in and around Lac Alaotra, in northeast Madagascar. The Alaotran lemur is the only primate specifically...
(Hapalemur griseus alaotrensis). The Alaotra Gentle Lemur is now limited to only 220 square kilometres (84.9 sq mi) of remaining reedbeds, and in recent years the lemur population rapidly declined by 60%, from approximately 7,500 individuals in 1994 to 3,000 in 2001, mostly from habitat loss, but also from hunting by local villagers.
The lake is also an important but increasingly threatened habitat for waterbirds, including the endangered Meller's Duck
Meller's Duck
Meller's Duck is a species of the dabbling duck genus Anas. It is endemic to eastern Madagascar. Although a population was established on Mauritius in the mid-18th century, this is on the verge of extinction due to habitat loss and competition by feral domestic ducks...
(Anas melleri). Two waterbird species were endemic to northern Madagascar, the Madagascar Pochard
Madagascar Pochard
The Madagascar Pochard is an extremely rare diving duck of the genus Aythya, previously thought extinct. Prior to a rediscovery in 2006, the last confirmed sighting of the species was at Lake Alaotra on the Central Plateau of Madagascar in 1991...
(Aythya innotata) and the Alaotra Grebe
Alaotra Grebe
The Alaotra Grebe , also known as Delacour's Little Grebe or Rusty Grebe, was a grebe endemic to Lake Alaotra and surrounding lakes in Madagascar. The last sighting was in 1985 and the species was declared extinct in 2010...
(Tachybaptus rufolavatus. The Madagascar Pochard is now critically endangered and no longer found on the lake itself, although very small numbers exist elsewhere. The Alaotra Grebe was declared extinct in 2010. In earlier times, Lake Alaotra was where the largest numbers lived, the near-flightless grebe may never have occurred elsewhere except in the immediate area of the lake.
The Ambato River provides the Lake with water and also drains it. After 381 km the river flows into the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
.