Variation of physico-chemical parameters along a river transect through the Okavango Delta,Botswana

The Okavango Delta depends on water quantity and quality to sustain its ecosystem services. Whereas many studies have been carried out on its hydrology, few have been done on water quality in the delta. Water pH, electrical conductivity (EC), dissolved oxygen (DO), turbidity, total suspended solids (TSS) and dissolved organic carbon (DOC) were monitored at 10 sites along the Okavango–Boro–Thamalakane–Lake Ngami system almost fortnightly from June 2008 to June 2010. Water quality in the delta was generally good, despite high evapotranspiration rates which would normally produce very saline waters. Electrical conductivity and water temperature increased with distance from Mohembo to Lake Ngami, the former most likely due to evapoconcentration. In contrast, pH, DO, turbidity and TSS decreased with distance from Mohembo to Boro at the lower end of the seasonal floodplain, before increasing again to Lake Ngami. Dissolved oxygen and TSS most likely declined due to biological uptake and particle sedimentation, respectively. Strong and significant relationships were observed between TSS and turbidity and between DOC and EC, indicating that turbidity and EC could be useful proxies for routine estimations of TSS and DOC, respectively, in the delta.     

River-wetland interaction and carbon cycling in a semi-arid riverine system: the Okavango Delta, Botswana

The Okavango River, in semi-arid northwestern Botswana, flows for over 400 km in a pristine wetland developed on a large (>22,000 km²) alluvial fan (Okavango Delta). An annual flood pulse inundates the floodplains of the wetlands and travels across the Delta in 4–6 months. In this study, we assess the effects of long hydraulic residence time, variable hydrologic interaction between river–floodplain–wetland and evapotranspiration on carbon cycling. We measured dissolved inorganic carbon (DIC) concentrations and stable carbon isotopes of DIC (δ¹³C_DIC) from river water when the Delta was not flooded (low water) and during flooding (high water). During low water, the average DIC concentration was 31 % higher and the δ¹³C_DIC 2.1 ‰ more enriched compared to high water. In the lower Delta with seasonally flooded wetlands, the average DIC concentration increased by 70 % during low water and by 331 % during high water compared to the Panhandle with permanently flooded wetlands. The increasing DIC concentration downriver is mostly due to evapoconcentration from transpiration and evaporation with increased transit time. The average δ¹³C_DIC between low and high water decreased by 3.7 ‰ in the permanently flooded reaches compared to an increase of 1.6 ‰ in the seasonally flooded reaches. The lower δ¹³C_DIC during high water in the permanently flooded reaches suggest that DIC influx from the floodplain-wetland affects river’s DIC cycling. In contrast, higher river channel elevations relative to the wetlands along seasonal flooded reaches limit hydrologic interaction and DIC cycling occurs mostly by water column processes and river-atmospheric exchange. We conclude that river-wetlands interaction and evapoconcentration are important factors controlling carbon cycling in the Okavango Delta.     

Mapping inundation extent,frequency and duration in the Okavango Delta from 2001 to 2012

The frequency and duration of inundation in river systems are important for a variety of applications, such as water resource management, floodplain mapping and habitat restoration. The Okavango Delta, the fifth largest Ramsar site in the world, has experienced a series of large floods since 2007, following the much lower flooding of the 1990s and early 2000s. This study aimed to establish inundation frequency and duration maps of the Okavango Delta for 2001 to 2012 using MOD09Q1 and MOD11A1. An earlier methods paper testing MODIS for flood mapping in the delta showed 99.4% overall accuracy for inundation mapping of the delta, with a kappa coefficient of 80%. A method based on a time-varying threshold derived from bimodal single-band histograms was used to classify the images into inundated and non-inundated areas. The method relies on the difference in reflectance between waterbodies and dry or vegetated soil, with the former having low reflectance and the latter displaying higher reflectance values. The method takes into account seasonal changes in reflectance. Inundation maps showed a gradual decrease in the delta's maximum annual inundation extent from 2001 to 2003, followed by a gradual increase from 2004 to 2012, with maximum inundation extent during 2010–2012.     

Symbiotic performance of grain and wild herbaceous legumes in the Okavango Delta and Tswapong region of Botswana

The low inherent soil fertility, especially nitrogen (N) constrains arable agriculture in Botswana. Nitrogen is usually added to soil through inorganic fertilizer application. In this study, biological nitrogen fixation by legumes is explored as an alternative source of N. The objectives of this study were to measure levels of N₂ fixation by grain legumes such as cowpea, Bambara groundnut and groundnut in farmers’ fields as well as to estimated N₂ fixation by indigenous herbaceous legumes growing in the Okavango Delta. Four flowering plants per species were sampled from the panhandle part of the Okavango Delta and Tswapong area. Nitrogen fixation was measured using the ¹⁵N stable isotope natural abundance technique. The δ¹⁵N values of indigenous herbaceous legumes indicated that they fixed N₂ (?1.88 to +1.35 ‰) with the lowest value measured in Chamaecrista absus growing in Ngarange (Okavango Delta). The δ¹⁵N values of grain legumes growing on farmers’ fields ranging from ?1.2 ‰ to +3.3 ‰ indicated that they were fixing N₂. For grain legumes growing at most farms, %Ndfa were above 50% indicating that they largely depended on symbiotic fixation for their N nutrition. With optimal planting density, Bambara groundnuts on farmers’ fields could potentially fix over 90 kg N/ha in some parts of Tswapong area and about 60 kg N/ha in areas around the Okavango Delta. Results from this study have shown that herbaceous indigenous legumes and cultivated legumes play an important role in the cycling of N in the soil. It has also been shown that biological N₂ on farmer’s field could potentially supply the much needed N for the legumes and the subsequent cereal crops if plant densities are optimized with the potential to increase food security and mitigate climate change.     

Potential environmental impacts associated with the proposed abstraction of water from the Okavango River in Namibia

The Namibian Department of Water Affairs has in the past faced considerable pressure to relieve the water shortages caused by recent droughts. One of the options considered in 1996, following poor runoff during the 1994/95 and 1995/96 seasons, was a proposal to abstract some 17Mm³ of water per year from the Okavango River at Rundu, and transfer this via a 260km long pipeline to the head of the Eastern National Water Carrier at the town of Grootfontein. Part of the overall evaluation of this scheme included an assessment of the potential environmental impacts that could arise. An initial environmental evaluation was conducted from a point approximately 40 kilometres upstream of Rundu in Namibia, to the distal end of the Okavango Delta at Maun in Botswana.

Hydrological studies showed that the proposed abstraction represented a reduction of approximately 0.32% in the mean annual flow of the Okavango River at Rundu. The abstraction represents 0.17% of the mean annual flow at Mukwe, downstream of the Cuito River confluence. The adverse effects of the proposed water abstraction scheme would be extremely small along the Okavango River in Namibia, whilst outflows from the lower end of the Okavango Delta to the Thamalakane River would be reduced by some 1.44Mm³/year (11%). Additional studies showed that these effects could be reduced by some 10–13% if abstraction was confined to the falling limb of the hydrograph.

Hydrological simulations have shown that the maximum likely loss of inundated area in the Okavango Delta would total approximately 7km² out of some 8 000km². This potential loss in inundated area would be concentrated in the lower reaches of the seasonal swamps and seasonally inundated grasslands, specifically in the lower reaches of the Boro, Gomoti, Santantadibe and Thaoge channels. However, these effects would most likely be expressed as a shoreline effect, with the loss in area spread out over the shoreline and periphery of islands and would not be restricted to a single specific area. This anticipated loss in inundated area is unlikely to have measurable impacts on environmental components.

Overall, the study found no 'fatal flaws' which would prevent the water abstraction scheme from proceeding and the anticipated effects on the Okavango system are more likely to be seen in the Okavango Delta, rather than along the Okavango River. The anticipated ecological implications of the scheme were small in spatial extent and are unlikely to be perceptible against the natural year-to-year variability in inundation of the Okavango Delta or outflows to the Thamalakane River. However, the public perceptions of the proposed water transfer project were strongly negative and appeared to be at least in part due to the very low water levels in the Okavango River and Okavango Delta during the past three years and during the study period. These low water levels were amongst the lowest on record and it is likely that the public would attribute any adverse effect recorded in the future to the abstraction scheme, whether this were true or not. These negative perceptions of the desirability and acceptability of the proposed scheme were strongly linked to potential adverse affects on the tourism industry along the Okavango River and in the Okavango Delta, with possible adverse economic effects on local residents.     

How landscape scale changes affect ecological processes in conservation areas: external factors influence land use by zebra (Equus burchelli) in the Okavango Delta

Most large‐bodied wildlife populations in sub‐Saharan Africa only survive in conservation areas, but are continuing to decline because external changes influence ecological processes within reserves, leading to a lack of functionality. However, failure to understand how landscape scale changes influence ecological processes limits our ability to manage protected areas. We used GPS movement data to calculate dry season home ranges for 14 zebra mares in the Okavango Delta and investigated the effects of a range of landscape characteristics (number of habitat patches, mean patch shape, mean index of juxtaposition, and interspersion) on home range size. Resource utilization functions (RUF) were calculated to investigate how specific landscape characteristics affected space use. Space use by all zebra was clustered. In the wetter (Central) parts of the Delta home range size was negatively correlated with the density of habitat patches, more complex patch shapes, low juxtaposition of habitats and an increased availability of floodplain and grassland habitats. In the drier (Peripheral) parts of the Delta, higher use by zebra was also associated with a greater availability of floodplain and grassland habitats, but a lower density of patches and simpler patch shapes. The most important landscape characteristic was not consistent between zebra within the same area of the Delta, suggesting that no single foraging strategy is substantially superior to others, and so animals using different foraging strategies may all thrive. The distribution and complexity of habitat patches are crucial in determining space use by zebra. The extent and duration of seasonal flooding is the principal process affecting habitat patch characteristics in the Okavango Delta, particularly the availability of floodplains, which are the habitat at greatest risk from climate change and anthropogenic disturbance to the Okavango's catchment basin. Understanding how the factors that determine habitat complexity may change in the future is critical to the conservation of large mammal populations. Our study shows the importance of maintaining flood levels in the Okavango Delta and how the loss of seasonal floodplains will be compounded by changes in habitat configuration, forcing zebra to change their relative space use and enlarge home ranges, leading to increased competition for key resources and population declines.     

Response of riparian plant communities to distance from surface water in the Okavango Delta,Botswana

The objective of this study was to determine the influence of distance from surface water on riparian woodland communities in the Okavango Delta. Vegetation sampling was conducted in seven sites within the Okavango Delta in 20 m × 10 m belted plots placed perpendicular to the river bank. The plots were placed at 0–10 m, 10–20 m, 20–30 m, 30–40 m and 40–50 m distance classes increasing away from the river bank. Tree height, basal area, species richness, canopy cover and diversity were determined for each distance class. Indicator species analysis was used to determine the characteristic species at each distance class. Single‐factor ANOVA and Tukey post hoc analysis were used to compare species diversity, mean tree height, cover and basal area between distance classes. Correlation between distance from surface water and vegetation parameters was sought using Spearman regression analysis. All parameters except for species richness varied significantly (P < 0.05) along distance from surface water. Distance from surface water was positively correlated all vegetation parameters except for mean species richness/plot. These results show that distance from surface water influences riparian plant community composition and distribution in the Okavango Delta. This implies that riparian plant species can be indicators of long‐term hydrologic conditions in the Delta.     

Estimating demographics of the Nile crocodile (Crocodylus niloticus Laurenti) in the panhandle region of the Okavango Delta,Botswana

The population status of the Nile crocodile (Crocodylus niloticus Laurenti) in the panhandle region of the Okavango Delta, Botswana, was assessed using mark–recapture and spotlight survey techniques following a decline because of commercial utilization. A total of 1717 individuals, ranging from 136 to 2780 mm in Snout Vent Length, were captured over a 4‐year period. Eighty‐one per cent of young juveniles encountered were successfully captured, representing 59.3% of total captures and 75% of recaptures. A Bayesian technique was used to estimate the number of young juveniles, and these estimates were then extrapolated for the other size classes. Survival and recapture analyses highlighted individual size‐dependent increases in wariness and survival. The total annual population was estimated to be 2570 ± 151.06 individuals, with an adult population of 649.2 individuals, including 364 females. We suggest that the harvest of breeding animals for commercial purposes should be halted until population recovery in this region is established.     

Community ecology and conservation of the fishes of the Okavango Delta,Botswana

Synopsis The Okavango Delta is a large inland swamp in northern Botswana which receives an annual flood from the highlands of southern Angola. There are distinct fish taxocenes in the Okavango which can be separated from each other by the physical characteristics of the different habitat types with which they co-evolved. An account is given of the ecology and conservation of the fishes of the Okavango Delta. Their response to the annual flood regime, and the environmental factors that limit their distribution and abundance, are described. In the northern riverine floodplain and perennial swamp a higher species richness and ichthyomass was recorded than in the seasonal swamp and drainage rivers. Suggestions are made on the conservation of Okavango fishes taking into account the ecological characteristics of the Delta.     

Do steady state assemblages occur in shallow lentic environments from wetlands?

The Okavango Delta has an annual flood cycle that spreads slowly from the northwestern`panhandle' into a widening delta to the southeast. Rotifers were sampled from areas where the flood was active, and from other areas not yet reached by the flood. In still waters, the samples were dominated by euplanktonic rotifers, particularly of the genera Brachionus, Keratella and Hexarthra, with about 20 species per 1000 individuals at a station. Where the water was moving the samples were dominated by periphytic rotifers, with over 100 species per 1000 individuals at a single station. The periphytic species were dominated by the genus Lecane,with over 45 species, followed by Lepadellawith 24 species, and Trichocercawith 23 species. Comparison of the Okavango with six other tropical localities reveals fairly consistent ratios of the numbers of species in the periphytic genera Lecane, Lepadellaand Trichocerca,indicating that there may be assembly rules for communities of tropical periphytic rotifers.     

Influence of the annual flood-pulse on catch per unit effort,condition and reproduction of Clarias gariepinus from the upper Okavango Delta,Botswana

Catch per unit effort (CPUE), length, weight and maturity data for Clarias gariepinus were collected during monthly gillnet surveys in the upper Okavango Delta between 2001 and 2009 to investigate their relationship with the annual flood-pulse. CPUE, condition factor (K) and the proportion of ripe-running fish (P_RR) in the population followed a unimodal annual cycle that could be modelled using water temperature and flood-pulse hydrology. Increased CPUE during declining water levels was most likely a result of feeding migrations and aggregation behaviour. The observed increase in K during low floods in October and November preceded the increase in P_RR, which increased mainly with increasing temperature but appeared less dependent on flow. This study provided quantitative evidence that the biology of fish in the Okavango Delta is mainly dependent on the annual flood regime and, therefore, that conservation efforts should be focused on maintaining natural flow patterns in the face of climate change and potential water extraction schemes upstream.     

Spatial and temporal variations in densities of small fishes across different temporary floodplain types of the lower Okavango Delta,Botswana

Small-sized and juvenile fishes as well as physicochemical water parameters in various primary, secondary and rarely flooded temporary floodplains of the Okavango Delta were assessed during the different hydrological phases of the 2009–2010 flooding season. Small fishes were sampled in the marginal zone of the floodplains using a throw-trap net and a suite of physicochemical properties were measured. Both physicochemical water quality parameters and densities of small fishes showed spatiotemporal variations across the temporary floodplain types. Turbidity, dissolved oxygen, conductivity, woody debris and chlorophyll a were all highest in rarely flooded floodplains compared to both primary and secondary floodplains (ANOVA, p < 0.05). Fish from 38 fish taxa belonging to 11 families were identified and classified during the study. The fish families Cichlidae (dominated by tilapias), Poeciliidae (Aplocheilichthys spp.) and Cyprinidae (Barbus spp.), were the most abundant across the study floodplains. The poeciliids were most abundant in frequently flooded primary and secondary floodplains, whereas juvenile cichlids dominated in rarely flooded floodplains. During high floods the rarely flooded portions of the delta function as important nursery habitats for juvenile cichlids, implying that a significant reduction in flooding may have negative effects on the delta's tilapia stocks due to reduced recruitment success.     

The Noble Savage Reconfigured: Paradox and Mimesis on Safari in the Okavango Delta,Botswana

ABSTRACT

Tourists to Africa covet close encounters with dangerous wildlife, revelling in the simulation of the primal risks of the savannah, and yet they expect to be kept safe. Similarly, many tourists wish to engage with exotic local people, but in ways that ensure they feel comfortable socially and physically. Safari guides in the Okavango Delta fulfil these desires by facilitating close encounters with wildlife during luxury camping safaris, while becoming objects of fascination themselves as they perform the role of the ecologically noble savage. The exoticness of a number of these Botswana citizens is, however, rendered familiar and comfortable for tourists through the fact of their whiteness. In this paper, I explore the paradoxes evident within Okavango Delta tourism, with a focus on the ‘familiar exotics’ guiding tourists through landscapes constructed around notions of ‘safe danger’. In making sense of this paradigm, I argue that mimesis is at play within white citizens’ embodiment and commodification of cultural values and practices normatively associated with indigenous peoples. This case demonstrates that within the tourism nexus, the ecologically noble savage trope evident in romanticised global imaginaries of indigeneity has largely failed to empower Botswana’s indigenous Bushmen communities, while perpetuating white privilege.     

Environmental change over two decades since dredging and excavation of the lower Boro River, Okavango Delta, Botswana

The Okavango Delta, southern Africa's largest wetland, is situated on the fringe of the semi-arid Kalahari Desert. It is a large alluvial fan, occupying a graben structure which is an extension of the East African Rift system. Of the 16 km³ of water which enters the Delta each year, 96% is lost to the atmosphere by evapotranspiration, 2% to groundwater and only 2% leaves as surface flow. In order to increase surface outflow to meet human needs, the distal Boro channel–floodplain system was dredged, excavated and bunded between 1971 and 1974. The immediate impact of these measures was the destruction of in-channel flora. After 20 years, the aquatic flora has recovered in the excavated channel. However, little recovery has occurred along the channel reach which was dredged. Moreover, there has been significant encroachment of terrestrial species onto the floodplain in the region of the dredged channel. In addition, dredging created a nick point which has been migrating upstream by headward erosion since dredging ceased. The average rate of advance of the nick point has been about 500 m per year. Incision associated with nick point migration has produced a channel which is indistinguishable in form from the dredged channel and, like the dredged channel, is almost completely devoid of in-channel aquatic flora. The adverse environmental impact of dredging has therefore continued to propagate in an upstream direction, although the height of the nick point has decreased, suggesting a natural attenuation process. This is likely to result in eventual elimination of the nick point.     

Assessing environmental and physiological controls over water relations in a Scots pine (Pinus sylvestris L.) stand through analyses of stable isotope composition of water and organic matter

This study investigated the influence of meteorological, pedospheric and physiological factors on the water relations of Scots pine, as characterized by the origin of water taken up, by xylem transport as well as by carbon isotope discrimination (Delta13C) and oxygen isotope enrichment (Delta18O) of newly assimilated organic matter. For more than 1 year, we quantified delta2H and delta18O of potential water sources and xylem water as well as Delta13C and Delta18O in twig and trunk phloem organic matter biweekly, and related these values to continuously measured or modelled meteorological parameters, soil water content, stand transpiration (ST) and canopy stomatal conductance (G(s)). During the growing season, delta18O and delta2H of xylem water were generally in a range comparable to soil water from a depth of 2-20 cm. Long residence time of water in the tracheids uncoupled the isotopic signals of xylem and soil water in winter. Delta18O but not Delta13C in phloem organic matter was directly indicative of recent environmental conditions during the whole year. Delta18O could be described applying a model that included 18O fractionation associated with water exchange between leaf and atmosphere, and with the production of organic matter as well as the influence of transpiration. Phloem Delta13C was assumed to be concertedly influenced by G(s) and photosynthetically active radiation (PAR) (as a proxy for photosynthetic capacity). We conclude that isotope signatures can be used as effective tools (1) to characterize the seasonal dynamics in source and xylem water, and (2) to assess environmental effects on transpiration and G(s) of Scots pine, thus helping to understand and predict potential impacts of climate change on trees and forest ecosystems.     

Spatial variations of microinvertebrates across different microhabitats of temporary floodplains of lower Okavango Delta,Botswana

Temporary floodplains of the Okavango Delta have been suggested as important nursery sites for juvenile fish. Fish production in the Delta is dependent on how well temporary floodplains are maintained. A study was conducted to understand how floodplains function so as to put measures in place that will sustain temporary floodplains in a high productive state. During high floods, distinct microhabitats (open water, sedges and inundated terrestrial grasses) develop in which microinvertebrate community structure was assessed across such habitats during the 2009–2010 flooding season. Depth was highest (ANOVA, P < 0.05) in the open‐water microhabitat and lowest within inundated grasses. Conductivity, total phosphorus and chlorophyll a were all highest (ANOVA, P < 0.05) within inundated grasses than in other microhabitats. A total of 46 microinvertebrate taxa were identified, and they were most diverse within the sedges. The abundance of microinvertebrates was highest (ANOVA, P < 0.05) within the inundated grasses and lowest within the open‐water zone. Given that microinvertebrates are an important food source for juvenile fish, their presence in high densities within inundated terrestrial grasses is a key determinant of fish production. This suggests the need for serious consideration of the importance of temporary floodplains when formulating conservation strategies for the Okavango Delta.     

A LIMNOLOGICAL PROFILE OF THE UPPER OKAVANGO DELTA AT LOW WATER LEVEL

Summary

Selected limnological attributes of the Okavango Delta panhandle were measured during a brief summer survey of “open-water” habitats extending from the permanent mainstream channel, through contiguous off-channel lagoons and still backwaters, to seasonally isolated floodplain lagoon and temporary pool biotopes on the left-bank of the Okavango River at Seronga.

Wide ranges in most determinants were evident along this profile:- temperature (27–34°C); conductivity(4–12.7mS m^?1); pH(5.7–9.2); transparency(0.2–>2.5 m Secchi depth); dissolved oxygen (20–220% saturation); PO₄-P (61–110 μg ?^?1): SiO₂—Si (6.9–14.0 mg ?^?1): NH₄-N (30–44 μg ?^?1): chlorophyll (1.3–183 μ.g ?^?1). Zooplankton was variably diverse (species richness from ≥ 3 to 20), comprising both euplanktonic (Bosmina, Ceriodaphnia, Daphnia, Diaphanosoma, Moina, Mesocyclops, Thermocyclops, Tropodiaptomus) and more typical epiphytic crustacean taxa (Alona, Macrothrix, Pleuroxus), along with various rotifers (Brachionus, Hexarthra, Keratella, Trichocera) and other taxa (Arcella, Ostracoda. Chaoborus). Abundance varied widely between habitats. The littoral macrozoobenthos showed surprisingly low diversity, and was dominated by freshwater shrimps (Caridina).

Substantial allochthonous inputs to the Okavango swamps were evident from the significant concentrations of total suspended solids (7.6–12.6 mg ?^?1 , organic content of 33–41%) carried by the mainstream Okavango River during the survey.     

Freshwater snails of East Caprivi and the lower Okavango River Basin in Namibia and Botswana

A systematic account is given of the aquatic gastropod fauna of the lower Okavango River in Namibia and Botswana, and of the East Caprivi area in Namibia, based on collections made mostly in 1983–86 from about 100 different sites. A total of 20 living species are reported, 9 of them for the first time from this area: Bellamya monardi, Lobogenes michaelis, Cleopatra elata, Afrogyrus coretus, Segmentorbis angustus, S. kanisaensis, Bulinus scalaris, B. depressus and B. tropicus. All are found outside this area and most are widely distributed Afrotropical species. Some do not occur farther south than the Okavango Delta, while others reach a south-western limit here but occur at greater latitude in the eastern tropical corridor on the coast of Natal. Bulinus globosus and Biomphalaria pfeifferi occur throughout the study area and are intermediate hosts for schistosome parasites of man and livestock.     

Two genotypic groups of morphologically similar fish trypanosomes from the Okavango Delta, Botswana

Blood smears and blood lysate samples from freshwater fishes captured in the Okavango Delta, Botswana, were examined to determine whether their trypanosomes were all Trypanosoma mukasai, a species of supposed broad host specificity and widespread existence across Africa. Trypanosomes and/or babesiosomes occurred in 20/32 blood smears, and morphometric analysis of trypanosomes from 13/32 smears showed features suggestive of T. mukasai, including nuclear indices consistently >1. In 16/32 blood lysate samples from which DNA was extracted, trypanosome DNA was detected in 12/16 by PCR (polymerase chain reaction), using trypanosome-specific ssu rRNA gene primers. Two samples positive for trypanosomes in blood smears yielded no amplifiable trypanosome DNA, but 4 samples with no detectable infection in blood smears were positive for trypanosome DNA, suggesting an overall trypanosome prevalence rate of 17/32 (53%) among fishes and demonstrating the value of PCR in trypanosome recognition. Cloning and sequencing of the 12 amplified fragments revealed 2 genotypic groups among these fish trypanosomes. Group 1 trypanosomes were from cichlids and 3 families of catfishes, Group 2 from 2 types of catfishes. Sequence comparison showed that the consensus Group 1 sequence was most similar to that of Trypanosoma cobitis, representing European fish trypanosomes of the carassii type, while the consensus Group 2 sequence showed similarity with a trypanosome sequence from another African catfish, Clarias angolensis. It was concluded that the identification of T. mukasai remains a problem, but at least 2 genotypic groups of trypanosomes occur in Okavango Delta fishes, and catfishes in this region appear to contain both types.     

The proportion of different eco-ethological sections of reproductive guilds of fishes in some African inland waters

Synopsis The continent of Africa has a wide variety of inland waters ranging from rift valley lakes to endorheic and coastal lakes, floodplains and rivers. This paper makes a preliminary comparison of the number of species in different eco-ethological sections of the reproductive guild categories of non-guarders, guarders and bearers in ancient African Great Lakes (Malawi, Victoria and Tanganyika), fluctuating endorheic lakes (Ngami, Chad and Chilwa), typical rivers (Orange-Vaal, Limpopo, Phongolo, Sabi-Lundi, Middle and Lower Zambezi, Kafue, Cunene, Okavango, Niger, Luongo, Lower Zaire) and wetlands (Okavango Delta and Kafue floodplain). The results indicate that the highest percentage of bearers and guarders is found in the ancient African Great Lakes, which are characterised by relatively predictable physico-chemical regimes, whereas a higher percentage of non-guarders is found in the rivers and wetlands, which have less predictable physico-chemical regimes. The management implications of this observation are discussed, and the usefulness of the species as a unit in ecology is assessed.