|Freshwater||172||37||No||Daget, J., J.-P. Gosse and D.F.E. Thys van den Audenaerde, 1984|
|Conservation||Knowledge of the status of freshwater fishes in Madagascar is very good. An overview of the fishes of the inland waters was published in 1994 (Stiassny and Raminosoa, 1994). Recommendations for a Conservation Strategy for the island’s fishes were published in 1991 (Reinthal and Stiassny, 1991). Madagascar is the world’s fourth largest island. It is separated from the African mainland by the Mozambique Channel, some 235 km wide at its narrowest point. The island’s relief can be described in terms of three large zones: an elevated central plateau; a steep eastern escarpment and narrow strip-like coastal plain; and an extensive low-lying western sedimentary plain. Just over 1% of the island’s area is comprised of open inland waters. The island can be divided into five major groups of basins. 1. The slopes of Mont D’Ambre. This volcanic massif in the extreme north is drained by numerous small torrents with narrow and elongate basins. 2. The Tsaratanana slopes. The rugged Tsaratanana massif in the north has rivers characterised by extremely steep gradients in their upper reaches, leveling off on the western and eastern coastal plains. 3. The Eastern slopes. Most of the eastern rivers are short with accentuated profiles. Along the narrow coastal plain the rivers meander and ultimately supply a chain of lagoons separated from the Indian Ocean by a range of sand dunes and spits. 4. The Western sedimentary plain. The western slopes make up almost 60% of Madagascar’s total area and the rivers of the western and northwestern slopes drain into the Mozambique Channel. The rivers can be divided into two groups. The first is comprised of the large rivers which flood widely over the Central Plateau. They often terminate in huge deltas with extensive mangrove development. The second group is comprised of smaller coastal streams flowing in between the large basins of the west, and whose sources are on the western edge of the plateau. 5. The Southern plain. The southern slopes experience a very marked dry season and an erratic wet season and as a result few southern rivers carry water to the sea throughout the year. Much of the south has no surface water whatsoever. The major threat to Madagascan fishes is habitat degradation as a result of deforestation and intrusive agricultural practices. This is accentuated by the effects on introduced species. Over 25 species have been introduced into Madagascar’s waters, some of which are now of considerable economic importance. A further compounding problem in large areas of the country is the spread of the introduced water hyacinth where their growth causes blockages and reduces water flow, increasing siltation. The increase in the use of aerial spraying of insecticides on commercial cotton plantations is also a cause for concern because of run-off into freshwater ecosystems. Current knowledge is insufficient to develop a comprehensive conservation programme in Madagascar. In the face of rapid depletion of the freshwater resources it is vital that on-going survey programmes are supported and that a thorough taxonomic revision of endemics is undertaken so that a plan for freshwater conservation can be integrated into on-going conservation programmes on the island. Contact: Melanie L.J. Stiassny, American Museum of Natural History, Department of Ichthyology and Herpetology, New York, NY 10024, USA.|
|Geography and Climate||
The country consists of the main Island of Madagascar and some smaller offshore islands. Total surface area is 581,540 km2. The main island consists of a central high plateau between 1,000 and 2,000 m in altitude which falls away steeply on all sides to a narrow coastal belt.
The central islands have a temperate climate with a single rainy season from November to April. The coastal regions have a tropical climate. On the north and west coast rains are light, whereas on the south and east rains are heavy and continuous throughout the year.
Ref. Vanden Bossche, J.-P. and G.M. Bernacsek, 1990
Lakes: there are hundreds of small and medium-sized lakes. Many are associated with the floodplains of westward flowing rivers. There are also many small mountain and crater lakes. Totalling the lakes, reservoirs and coastal lagoons, there are some 530 lacustrine water bodies with surface areas over 0.20 km2 in Madagascar. The ten largest lakes are:
Alaotra - 200 km2
Kinkony - 139 km2
Ihotry - 94.2 km2
Itasy - 35 km2
Tsimanampetsotsa (saline) - 29.88 km2
Komanaomby - 18.1 km2
Bemamba - 15.9 km2
Hima - 15.5 km2
Mandrozo - 14.4 km2
Amparihibe - South - 12.5 km2
The total lake area in Madagascar is probably over 600 km2.
Rivers, floodplains and swamps: many rivers flow from the central highlands of Madagascar. The largest river basins 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 be greater than 2,000 km2. Swamps are associated with some lakes (i.e., Lake Alaotra).
Reservoirs: two medium-sized reservoirs (Mantasoa and Tsiazompaniry) with surface areas of 18.0 and 31.0 km2, respectively, are situated near the capital (Tananarivo).
Coastal lagoons: Madagascar has significant brackishwater resources. These consist of lagoons on the east coast and mangrove swamps grouped around the mouths of the main rivers on the west coast.
Ref. Vanden Bossche, J.-P. and G.M. Bernacsek, 1990