The African lakes descriptions are mostly skipped unnoticed because they often involve factual information that is for common breeder considerably distant and therefore does not pay them attention. Understanding lake and its surrounding, as a complicated biological complex will help in successful breeding of cichlids from the great African lakes, especially when it comes to exceptional conditions occurring therein, and also due to a number of endemic fish species. Aquarist will often try to emulate the habitats that are found in lakes, so information about the environment and communities of fish in these conditions may be useful. I hope this information can also be found in this 2-part article about one of the African lakes.
General characteristics of Lake Malawi
Lake Malawi, also known as Nyasa, lies in the southern part of East African Great Rift Valley. From north to south is nearly 600 km long with a maximum width of 80 km. Surface level is about 31 000 km2. The maximum depth is over 700 m. It is the third largest lake in Africa following Lake Victoria and Lake Tanganyika and in volume (7775 km3) it is 5-th in the world. Over 90% of the lake lies at a depth of 100 m. Its age is estimated at 2 to 20,000,000 years. It is surrounded by three countries. Coastline is about 1600 km. Most of the coastline belongs to one of the country with the same name, Malawi, which stretches almost along the entire west coast, includes the southern part and ends in the middle part of the east coast, a total of about 800 km. With the Mozambique it borders at about 200 km length of the central part of the east coast. The north-east coast and part of the north-west coast belongs to Tanzania, forming a 300 km coastline. The lake is still called Lake Nyasa in Tanzania and Mozambique, which in the original language of the Yao tribe means "good water". The most notable landmark is a huge mountains chain surrounding the lake from the north-west (north of Nkhata Bay) and the north-east (Livingstone Mountains). Surface water temperature varies between 23 to 29 ° C, pH between 7.9 to 9.1on the surface and 7.8 in a depth of 300 m, the surface conductivity is 215 to 225 µS. Visibility far from the coast is 12 to 20 meters, falling closer to shore. During the rainy season water level varies in the range of 0.7 to 1.8 m.
Copyright © Stuart Hulburt
Picture published with author permission
Lake Malawi is not only an important source of food, water, electricity for the people of Tanzania, Mozambique and Malawi, but it is also one of the biologically most diverse ecosystems on Earth. It contains more species than other lakes. Surviving farming increases soil erosion, runoff and sediment transport and caused damage to water quality of many rivers that flow into Lake Malawi. Eutrophication and increased sedimentation is causing serious problems to endemic fish species. Biomass burning and fertilization of soil also increases the atmospheric deposition of nutrients into the lake. These conditions increase the production of blue-green algae that are toxic to humans, animals and aquatic animals. Concentration of organic chlorine compounds also increases the in lake organisms.
Coastal sites are characterized by a number of homes, houses, boats and canoes and drying fish on racks. On the south bank, there is the densest human settlement. Fishing is important in the north of Makanjilla to the border with Mozambique. Most of the coastal communities in Malawi consist of less than 15 huts, so settlement is characterized by rather smaller settlements scattered along the coast. The largest concentration is in the southeast and north of Usisya. There are a few big sand platforms that are used less in comparison with the southern part. South-west part includes a strip of vegetation about 60 km long with dense stands of plants, which is uncommon for the lake. Many coastal areas in Tanzania and Mozambique are unpopulated. Gratings for drying fish were observed mainly on the east coast of the south part of the lake, south of Goma to the Shire River and in Nankumbe.
The area from which the lake receives water occupies 125 000 km2. Many rivers flows to the lake, the largest is Ruhuhu on the north-east, Songwe on the north, South Rukuru, Dwangwa, Bua and Linthippe on the west. Near Nkhotakota, Chia lagoon is connected with lake by a short river surrounded by reeds. Unake lagoon near Dwanfy and Mulale lagoon near Karonga are similar, but smaller. Chilingali Lake lies in a small river about 5 km inland near Nkhotakota and Lake Chiwondo is separated from the main Lake Malawi with narrow sandy strip. In both, populations of lake cichlids live. The only outflow from the lake is the Zambezi Shire river. After about 10 km slowly flowing upper stream of the Upper Shire expands and forms a highly productive, shallow lake Malombe with an average depth of 4 m. There is no barrier that would limit migration of fish between Lake Malawi and Malombe. The central part of the river, Middle Shire, leaves the south end of Malombe and last part of the Lower Shire flows into the Zambezi River.
Seasons in Lake Malawi basin
The area around Lake Malawi has three seasons. The cold season lasts from May to August-September. At that season the weather is the dry, cold and windy. Water is cloudy mainly in the south and strong winds make it impossible to fishing. Hot season begins in September and lasts until the first rains. It is very hot and dry and water is crystal clear. In this heat, however, fish breeding decreases. The rainy season is variable at the beginning. It may rain in November or December, but well rain will occur in January-March, April. During this period, similar processes as in the spring in the northern countries occur in nature. The first rains cause the blooming flowers and grass growth. The number of trees that dropped leaves during the dry season has new leaves. Temperature decreases and brings relief after a period of high temperatures. Mosquitoes are very abundant it is the highest risk of malaria in this period. Clarity of water near the river mouths is reduced. The temperature in the lake during heavy rain falls by about 2° C.
During the warm season, when the wind stops, the upper layer of water warms. The part where the plants grow is called the epilimnion, metalimnion is a middle part and of the deepest layer of oxygen-free is called hypolimnion (> 220 m). Each year, 25% of bottom layer of water mix with an intermediate layer and 20 to 25% of the middle part is mixed with the surface water layer. In January, the surface temperature is 27 to 29° C and in the wind and cold period it is 23 to 24° C. The middle layer has a temperature of 22.5 to 23.5° C and lower water layer has about 22.7° C. In colder periods, the surface layer is mixed with deeper waters (to about 100 m). Temperature differences between surface and deep layers of water decrease below 1° C. Recent research has highlighted the increasing temperature of deep layers of water by 0.18° C every 10 years.
During cold periods, winds waft from the south-east to north-west. Wind is locally called "mwera." The rivers rich in nutrients flow into the lake, especially in the southern part of the lake. This leads to increased production of fish in the lake (July-August), because many fish reproduce at this time. The next breeding peak is in April when the rainy season ends. read 2nd part »