Largest Lake In Madagascar

[Sofía Goldthwait]

LakeAlaotra (Malagasy: farihin' Alaotra, [faˈrihin ˈaloʈʂə̥]; French: Lac Alaotra) is the largest lake in Madagascar, located in Alaotra-Mangoro Region and on the island's northern central plateau. Its basin is composed of shallow freshwater lakes and marshes surrounded by areas of dense vegetation.[3] 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 wetlands cover 7,223 square kilometres (2,789 sq mi), and include a range of habitats, including open water, reedbeds, marshes, and rice paddies. The lake itself covers 900 km2 (350 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.[4]

The fertile plain surrounding 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 cm (24 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 km2 (85 sq mi) of remaining reedbeds, and in recent years, its population rapidly declined by 60%, from about 7,500 individuals in 1994 to 3,000 in 2001, mostly from habitat loss, but also from hunting by local villagers.

The lake is the type locality of the butterfly Artitropa alaotrana and 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, although very small numbers exist elsewhere. The Alaotra grebe was declared extinct in 2010. The area of the lake may have been its only habitat.[5]

The biomes of Madagascar are the savannah, the desert, the tropical forest, several types of mountain ecosystems and wetlands. The savanna is a dry meadow, while the desert is extremely dry and has little vegetation. The tropical forest is mainly located in the east of Madagascar. Mountainous ecosystems are at higher altitudes. The savannah is found along the west side of the island, where most of the rains fell on the east side. The desert is also on this side of Madagascar. Tropical forests are on the opposite side of the savannah and desert biomes because most of the rains have fallen there. And finally, the mountainous ecosystems are in the middle of Madagascar, where the elevation is higher.

The West Biome

Dry deciduous forests dominate in the west. In this region, the forests are in an altitude range of 0 to 800 m, but they present several varieties according to the different bioclimatic types. The physiognomy of the vegetation is characterized by a height of 25m with a closed canopy and well-defined undergrowth vegetation. The formation is a mixture of three types of vegetation: evergreen, sclerophyllous and dry (on rocky outcrops).

Southern Biome

The dry forests of the Southern Ecoregion cover an area of 57,721 square kilometers and are characterized by deciduous shrubs or thorny thickets that extend south from Morombe along the coast and cover most of the southern part of Madagascar from sea level up to 400 m. Rainfall in this region is low and erratic. These are the driest forests in Madagascar and the region is commonly known as the Spiny Desert. There remain approximately 19,131 square kilometers (33%) of intact original forest in the Southern Ecoregion

The Wetland areas

The wetlands of eastern Madagascar take the form of lakes, rivers and marshes. There are few large in the region but the largest lake in the country, Alaotra Lake, is there, as well as the system of acidic and barren coastal lagoons of Pangalanes. The most important wetlands in the east are marshes, usually constructed from small marshy vegetation areas at medium and high altitude, and often located in narrow valets or on the edges of lakes.

Malagasy coastal habitats differ considerably between the east and west of the island. The east has mostly sandy beaches sparsely populated with birds. The west is richer and more diverse with extensive mangroves, salt marshes, coastal lagoons, estuaries, sandbars, sandy beaches and offshore islands.

Lake Alaotra is the largest lake in Madagascar, and the surrounding wetlands are a major food producing region for Madagascar. The regions around Lake Alaotra are suffering from deforestation and erosion. Due to the cultural and economic importance of Lake Alaotra it has become of particular interest for restoration. Conservation International and the Priceless Planet Coalition have collaborated on a project to reforest the area. This project relies on stakeholder engagement and is led by the communities in the region. Community engagement and the expertise they provide is critical for successful conservation. The community involvement in the evaluation and monitoring is just as important, although there are many obstacles to monitoring and many projects are never evaluated. In particular, the cost of project evaluation is high, especially for water quality. A meter for water turbidity capable of mid to long-term deployment costs thousands of dollars. We aimed to create a sensor capable of mid to long-term deployment that was low cost and made from locally sourced parts. We heavily considered materials likely to be available in Madagascar as we created our design. In summer 2023, we built three sensors. One was built from parts almost entirely found in Madagascar. Two were deployed successfully for a week-long test period in study streams in the Alaotra-Mangoro region and one was used for local workshops. Over fall 2023 and spring 2024 we built two additional sensors that have been used to collect calibration data. The data from these tests has allowed us to refine the sensor design, improve deployment materials, and engage with community members

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Gully evolution remains poorly understood, largely because multidecadal analysis is lacking. Large gullies (called lavaka) that pepper Madagascar's highlands are generally attributed to human impact; but longitudinal data are few, and anthropogenic causation is inferred not verified. We focus on Lac Alaotra, Madagascar's largest lake and wetland, its major rice-growing region, and an ecological hotspot surrounded by fault-controlled steep hills with abundant lavaka. Analysis of historical aerial photographs and recent orthoimagery reveals that the proportion of highly active lavaka has decreased since mid-20th century. At the same time, human population, farming intensity, and livestock density have increased exponentially. This suggests that background factors, including seismicity, are primary drivers of lavaka formation. Although human activities may contribute to erosion overall, land management policies that overemphasize human causation of gullying and neglect background forcing factors (in Madagascar and elsewhere) are unlikely to be effective in erosion mitigation.

The country consists of the main Island of Madagascar and some smaller offshoreislands. Total surface area is 581 540 km2. The main island consists of a central highplateau between 1 000 and 2 000 m in altitude which falls away steeply on all sides to anarrow coastal belt.

The central islands have a temperate climate with a single rainy season fromNovember to April. The coastal regions have a tropical climate. On the north and westcoast rains are light, whereas on the south and east rains are heavy and continuousthroughout the year.

There are hundreds of small and medium-sized lakes. Many are associated withthe floodplains of westward flowing rivers. There are also many small mountain andcrater lakes. Totalling the lakes, reservoirs and coastal lagoons, there are some530 lacustrine water bodies with surface areas over 0.20 km2 in Madagascar.

Many rivers flow from the central highlands of Madagascar. The largest riverbasins drain to the west and floodplains are developed along the lower courses.Total floodplain area has been estimated at 918 km2 but the actual area may begreater than 2 000 km2. Swamps are associated with some lakes (i.e., Lake Alaotra).

The fishery has been developing at about 2% per year over the last 15 years.In some lakes (i.e., Lake Alaotra), accelerated fishery development occurred whenbetter fishing materials were introduced. Lake Itasy was over-exploited between1960 and 1965 and the stocks did not reconstitute themselves. Many of the otherareas, such as the Pangalanes, are recorded to be unproductive and intensivelyexploited.

No great increases in natural fish production can be anticipated from theinland and brackish waters of Madagascar. They are at present intensively exploitedand need rational management to maintain their present levels of productivity.Further growth of the inland fisheries sector could occur through fishculture and intensive management of inland water bodies by stocking and feeding.

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