Lakes Of Africa Research Articles

Distribution and breeding biology of offshore cichlids in Lake Malawi/ Niassa

Lake Malawi/Niassa is the second largest rift valley lake in Africa, with an area of 28 800 km2, and an average and maximum depth of 292 m and>700 m, respectively. The lake is well known for the great diversity of fish occurring in the inshore zone. However, the offshore fish community is poorly documented. To rectify this, regular sampling was undertaken over two years, using trawl and gillnets at six offshore locations. This paper reports on the species composition, spatial distribution and breeding biology of the dominant cichlids species from the offshore pelagic zone. Cichlids formed approximately 88% of the offshore fish biomass. Most abundant were two species of zooplanktivores in the genus Diplotaxodon that made up 71% of the offshore fish biomass. An undescribed species, given the cheironym D. ‘bigeye’, was mainly found at a depth of 220 m during the day, but moved into near surface waters at night when the moon was full. This species was absent from the shallow regions of the lake. The most abundant offshore species was D. limnothrissa, which was distributed evenly throughout the lake to depths of 220 m. A less common offshore zooplanktivore was Copadichromis quadrimaculatus that formed 5% of the biomass and was confined to the upper 100 m of the water column. The main piscivores were in the genus Rhamphochromis and formed approximately 10% of the offshore fish biomass. The two dominant taxa were R. longiceps and the ‘large Rhamphochromis’ group, and both were more common in the southern half of the lake. The former occurred mainly in the upper 100 m of the water column and the latter mainly at depths of 100–150 m. The length at maturity and fecundity for the dominant offshore species were estimated and seasonal breeding cycles determined from gonad activity and gonado-somatic indices.

Late Pleistocene Desiccation of Lake Victoria and Rapid Evolution of Cichlid Fishes

Lake Victoria is the largest lake in Africa and harbors more than 300 endemic species of haplochromine cichlid fish. Seismic reflection profiles and piston cores show that the lake not only was at a low stand but dried up completely during the Late Pleistocene, before 12,400 carbon-14 years before the present. These results imply that the rate of speciation of cichlid fish in this tropical lake has been extremely rapid.

Book reviews : Roder, W. 1994: Human adjustment to Kainji Reservoir in Nigeria: an assessment of the eco nomic and environmental consequences on a major man-made lake in Africa. Lanham, MD: University Press of America. 18 + 188pp. US $42.50 cloth, US $29.50 paper. ISBN: 0 8191 9333 X (cloth), 0 8191 9334 8 (paper)

Book reviews : Roder, W. 1994: Human adjustment to Kainji Reservoir in Nigeria: an assessment of the eco nomic and environmental consequences on a major man-made lake in Africa. Lanham, MD: University Press of America. 18 + 188pp. US $42.50 cloth, US $29.50 paper. ISBN: 0 8191 9333 X (cloth), 0 8191 9334 8 (paper)

The Great Lakes of Africa

The Great Lakes of Africa

Analysing Hydrometeorological Time Series for Evidence of Climatic Change

Considerable scientific attention has been focused on a measured increase in atmospheric CO2 and a suspected corresponding change in climate. Such a change in climate, if it occurred, might be expected to have a magnified effect on hydrologic time series and, indeed, projections have been made of major changes in water resources. If the climatic changes are indeed magnified in hydrologic time series then, by detecting trends in such series, it should be possible to work backwards and identify the causative climatic change. This paper looks at two data sets: 1) long-term temperature, precipitation and streamflow data from sites across Canada and 2) long-term levels of large lakes in Africa and North America. The study assumes that time series may be modelled by trend, periodic, autoregressive and random residual components. The trend component of a time series is generally associated with changes in the structure of the time series caused by cumulative natural or manmade phenomena. Periodicities in natural time series are usually due to astronomical cycles such as the earth's rotation around the sun. Autoregressive components reflect the tendency for an event to be dependent on the magnitude of the previous event(s), a memory effect. The analyses of temperature, precipitation and streamflow data show some significant linear trends but no pattern is apparent. The analyses of longterm lake levels also identify linear trends but these are all explainable without invoking climate change due to greenhouse gases.

Conservation and threats to the resources of Lake Malawi

Developments taking place in the countries bordering the Great Lakes of Africa inevitably mean that changes are occurring in the ecology of those lakes and that such changes will continue. The role...

Paleoclimate of the past 4000 years at Lake Turkana, Kenya, based on the isotopic composition of authigenic calcite

Authigenic calcite was analyzed for δ 13C and δ 18O in a 12 m long core from Lake Turkana that spans the last 4200 yr. The δ 18O record is interpreted to reflect lake level history, and indicates high stands prior to 4000 yr B.P., from 1800 to 2000 yr B.P., and within the last century. This coincides better with the history of lake level change reported for other lakes in africa than did the previous lake level curve for Lake Turkana based on 14C dates of exposed shoreline deposits. The δ 13C curve roughly parallels the δ 18O curve, and may reflect the influence of the Omo River plume. Both of the isotope records are strongly cyclic, with periodicites common to both at 80, 120, 150 and 225 yr. Other, somewhat longer periodicites are nearly equal in the two records, and there is close agreement with previously published cycles based on carbonate and lamination thickness analyses in the same Turkana core.

Major low levels of Lake Malawi and their implications for speciation rates in cichlid fishes

Lake Malawi, the third largest lake in Africa, is several million years old. Lake levels have fluctuated to a considerable extent in the late Pleistocene. Although tectonism may have influenced earlier level changes, the more recent changes have been climatically controlled. Major recessions occurred in the period before 25000 years ago and 10740 ± 130 years ago, with further large falls between 1150 and 1250 A. D. and within the period 1500-1850. The 1500-1850 lake recession-refilling cycle is documented by using a variety of techniques. Sediment cores show an erosional hiatus stretching across the southern area of Lake Malawi down to water depths of at least 121 m. Diatoms sharply decline in abundance and diversity across this break, withMelosira nyassensisdominating in the post-erosion period. During the low stage, exposed littoral sands were reworked into aeolian dune-fields along windward shorelines. Oral histories reflect a group memory of this low period, which is supported by14C dated archaeological finds in beach ridges surrounding the lake. Dating by210Pb methods show that lacustrine sedimentation had resumed by about 1860. At this time, early explorers, such as Livingstone, were reporting evidence of rising lake levels. Hydrological modelling shows that the lake-level changes indicated are possible in the timespan available. Various permutations of rainfall and timescale are discussed, e. g. a drop of 110 m over 250 years would require rainfall at 50% of modern values. The changes in lake level imply longterm changes in climate; these are highly relevant in the field of drought-risk assessment. The species flock of rocky-shore dwelling Lake Malawi cichlids known as ‘Mbuna’ contains about 200 species in Malawi’s waters. Mitochondrial DNA differentiation shows that the flock as a whole is of extremely recent origin. Almost every rocky outcrop and island has a unique Mbuna fauna, with endemic colour forms and species. As many of these islands and outcrops were dry land within the last 200-300 years, the establishment of the faunas has taken place within that time. The evolution of distinct forms in such a brief timespan is discussed in relation to current ideas on allopatric speciation. The present diversity of the Malawi cichlid-species flock, and particularly the Mbuna, may be readily explained by the rapidity with which small founder populations can diverge from the parent population, as demonstrated by the present chronological evidence on changes in lake levels and by the Mbuna distribution data. The repeated recessions and refillings of the lake have provided numerous opportunities for the establishment of different founder populations and consequently different selection pressures, leading to further bouts of speciation.

Big fish threaten Africa's big lakes

Big fish threaten Africa's big lakes

Destruction of fisheries in Africa's lakes

The introduction of the Nile perch into Lake Victoria, East Africa, has had disastrous consequences. Fisheries have been not merely damaged but destroyed. Lake Malawi has the world's most species-rich fish fauna and the prospect of introduction of alien species could mean disaster.

Monitoring Africa's Lake Chad basin with LANDSAT and NOAA satellite data

Abstract Data from the LANDSAT and NOAA polar orbiting satellites are used to analyse the Lake Chad basin in Africa. AVHRR measurements spanning the November 1981-November 1982 period are used to monitor lake boundaries, vegetation growth and surface temperature patterns. Historical LANDSAT data from the 1972-1981 period are studied to track changes in lake and basin boundaries. Observations of lake conditions, as viewed from satellites, are related to the recent climate record

Lake McIlwaine (The Eutrophication and Recovery of a Tropical African Man-Made Lake).

'And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. ' Genesis 1:6 Lake McIlwaine is a man-made lake. It was formed in 1952 by the Hunyani poort Dam and is situated on the Hunyani River some 37 km southwest of Salisbury* in the Republic of Zimbabwe**. It is a lake of many aspects: being a popular recreational site, the City's primary water supply reservoir (and the fourth largest impoundment in Zimbabwe), a source of irrigation water to downstream farms, an important fishery, and, until the 1970s, the receptacle of Salisbury's sewage effluent. It is, in short, typical of so many 'urban' lakes in Africa and throughout the world. Lake McIlwaine is also unique, to my knowledge: being amongst the first of the major man-made lakes on the continent to suffer from what is known as cultural eutrophication, and the first to be r: ehabilitated to a mesotrophic state through a rational programme of lake management. This volume synthesizes this process of eutrophication and recovery in terms of the geology and geography (Chapter 2), physics (Chapter 3), chemistry (Chapter 4) and biology (Chapter 5) of the lake, and, whilst discussion of the trophic relationships between these components is beyond the scope of this monograph, discusses its utilisation, conservation and management (Chapter 6). * Subsequent to writing, the name of the Zimbabwean capital was changed to Harare on 18 April 1982. - Ed.

Enzyme Variation in Haplochromine Cichlid Fishes From Lake Victoria

In the great lakes of Africa, endemism and high rates of speciation are characteristic for some genera within cichlid species flocks. These flocks present novel problems in differentiation and speciation. Much debate has centered around the actual way in which speciation has taken place in the African lakes and in particular whether or not the cichlid flocks provide an example supporting sympatric as opposed to allopatric speciation. To characterize evolutionary changes in some species of the presumed young species flock of Lake Victoria, we studied allozyme variation through electrophoretic analysis of muscle enzymes from 10 haplochromine species. The genetic similarities calculated between the 8 Haplochromis species are very high (genetic identities are all higher than 0.97). Even the monotypic genera Hoplotilapia retrodens and Macropleurodus bicolor are electrophoretically indistinguishable from members of Haplochromis. Based upon the available evidence, the species used here are biologically valid. Therefore it is argued that the very high genetic similarities reported here (and by other authors) are best explained by a very recent separation of the different haplochromine gene pools. This implies that the genetic differences, which did accompany reproductive isolation, involved either regulatory genes or non enzymatic parts of the structural genome. This is in accordance with the accepted views on the dominant factors in cichlid speciation.

Associations of rotifers in Australian crater lakes

Associations of rotifers in 12 Australian crater lakes have been compared by means of indices of similarity and diversity, and by two dimensional ordination. Four of the lakes lay on the Atherton Tableland in tropical Queensland, four were shallow saline lakes in Victoria and the remaining four were fresh lakes in the same general region as the saline lakes.The total number of species identified was 67, but the maximum found in any one sample was 27. Salinity is an important factor reducing diversity, whilst the development of vegetation increases the diversity of the rotifer fauna. The index of diversity (a) ranged from less than one in the saline lakes to 13 in the richly vegetated Lake Euramoo.Comparisons with the rotifers living in the open waters of crater lakes in Africa, Indonesia and Europe revealed no marked similarities between the fresh Australian lakes and these other regions, although strong similarities were found between Ausralian saline lakes and those of other regions. In general the rotiferan faunas of the Australian crater lakes resembled each other less than might be expected from the similarities found between crater lakes within other regions.

Nyumba ya Mungu reservoir, Tanzania: The general features

Nyumba ya Mungu reservoir was completed in 1965 in northern Tanzania. By 1970 there was a thriving tilapia fishery but it declined catastrophically in subsequent years. A team of biologists surveyed the lake in 1974, and this paper outlines their hydrological, geographical, and climatic findings. The dam, constructed across a north/south Neogene fault-trough 80 km south of Mt. Kilimanjaro, has produced a reservoir about 180 km2 with a mean depth of 6 m. The catchment area is extensive but the main source of water is from Mt. Kilimanjaro. The lake is situated in an arid area, and over one quarter of the input water evaporates from the lake's surface. The outflow is regulated by a hydro-electric power station and is practically constant. At full capacity the retention time of the lake is one year but due to abnormally low rainfall, the reservoir was not full, and the retention time was nearer nine months. The lake is polymictic and a deep wind-driven current is maintained by the Trade Winds for most of the year. The general features of Nyumba ya Mungu are briefly compared with other man-made and natural lakes in Africa.

Man-made lakes in Africa ? their benefits and problems

Man-made lakes in Africa ? their benefits and problems

The Cichlid Fishes of the Great Lakes of Africa: Their Biology and Evolution

The Cichlid Fishes of the Great Lakes of Africa: Their Biology and Evolution

Man's Role in Nature

Research Article| February 01 1975 Man's Role in Nature Roger Tory Peterson Roger Tory Peterson Search for other works by this author on: This Site PubMed Google Scholar The American Biology Teacher (1975) 37 (2): 90–93. https://doi.org/10.2307/4445087 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Cite Icon Cite Search Site Citation Roger Tory Peterson; Man's Role in Nature. The American Biology Teacher 1 February 1975; 37 (2): 90–93. doi: https://doi.org/10.2307/4445087 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentThe American Biology Teacher Search This content is only available via PDF. Copyright 1975 National Association of Biology Teachers Article PDF first page preview Close Modal You do not currently have access to this content.

The Cichlid Fishes of the Great Lakes of Africa. Their Biology and Evolution

The Cichlid Fishes of the Great Lakes of Africa. Their Biology and Evolution

The Cichlid Fishes of the Great Lakes of Africa

The Cichlid Fishes of the Great Lakes of Africa