Lake Kariba Research Articles

Managing Lake Kariba sustainably: threats and challenges

PurposeThe purpose of this paper is to communicate and share experiences with stakeholders on how the sustainability threats and challenges associated with managing Lake Kariba and the Kariba Dam wall are being managed by the Zambezi River Authority (ZRA).Design/methodology/approachThe case study area is Lake Kariba and Kariba Dam wall located in the mid‐Zambezi river basin. The data and information for the case study is from ZRAs own records.FindingsThe case study concludes that the threats and challenges so far experienced have been mitigated adequately with management programmes and tools having been put in place. However, a lot still needs to be done to improve the socio‐economic living conditions of the displaced Tonga/Korekore people.Originality/valueLake Kariba was created in the late 1950s to provide water primarily for hydro‐power production. However, this water resource now serves many users and has its sustainability threats; invasive weeds, water pollution, cyclic drought and flood events, the competing uses and multiple legislative provisions. The Kariba Dam wall, as an engineering structure, has its own sustainability challenges; effects of alkaline aggregate reaction, the spillway plunge pool stability and the general ageing of the dam structure. The Tonga/Korekore people, who were displaced on both banks of the Zambezi River when Kariba Dam was built, still feel short‐changed. Stakeholders will be able to associate and relate to similar threats, challenges and experiences and use the management solutions being applied at Kariba. The opinions and conclusions drawn in this case study are those of the author.

Seasonal variability of persistent organochlorine pesticide residues in marine fish along the Indian Ocean coast of Kenya

Organochlorine pesticide residues were analyzed in samples of fish taken from four different locations along the Indian Ocean coast of Kenya. Considering all the four sampling sites in the two sampling seasons, the ranges of concentrations of residues detected in the fish samples (in µg kg−1 wet weight) were: lindane 16.1 (in sample from Mombasa)–1445 (Sabaki), aldrin 1.55 (Kilifi)–323 (Kilifi), dieldrin 4.81 (Ramisi)–109 (Sabaki), endosulfan 5.91 (Mombasa)–54.6 (Sabaki), p,p′-DDT 9.11 (Mombasa)–29.3 (Kilifi), p,p′-DDE 1.94 (Kilifi)–97.5 (Sabaki) and p,p′-DDD 1.68 (Mombasa)–98.9 (Kilifi). The concentration ranges obtained in fish in this study indicate that Mombasa Old Town was least contaminated by organochlorine residues as higher residues were detected near Malindi, at Funzi Lazy lagoon and at Kilifi creek which were near the confluences of Rivers Sabaki, Ramisi and Goshi at the Indian Ocean coast, indicating that the sources of the residues in fish the Indian Ocean coast were through discharge from the rivers. Seasonal variation in concentration of residues detected in fish samples was clear, with higher residue levels being recorded in the rainy season in May compared with those detected in the dry season in January. This seasonal variation was particularly observable in p,p′-DDT residues which were only detected in samples taken in the rainy season but none in the dry season in all the sampling sites. The high DDT/DDE and aldrin/dieldrin concentration ratios also indicated that the sources of these residues were recent. This conclusion was also supported by high BCF values of lindane in fish sampled in Sabaki and of aldrin sampled from Kilifi and Ramisi. Overall, the concentration ranges of some of the residues such as DDT, DDE, and DDD were comparable with those reported earlier for fish samples from Lake Kariba in Zimbabwe but concentration ranges of lindane and aldrin were much higher than those reported in fish from Lake Kariba. The concentration ranges of the residues of dieldrin, lindane and DDE were comparable with those obtained in fish from Tana River in Kenya but the other residues of aldrin, endosulfan, DDD, and DDT were much higher than those detected in fish from River Tana.

Epiphytic diatoms associated with a submerged macrophyte, Vallisneria aethiopica, in the shallow marginal areas of Sanyati Basin (Lake Kariba): a preliminary assessment of their use as biomonitoring tools

Diatom assemblages attached to the leaves of the submerged macrophyte Vallisneria aethiopica in the shallow waters of the Sanyati Basin in Lake Kariba were analysed to assess their response to human impact. Human activities occurring within approximately 500 m of the shoreline were assessed at ten sampling sites along the shores of the basin. Eleven human activity factors were assessed and scored on a scale of 0 (not occurring at the site), 1 (low), 2 (medium) and 3 (high). Based on these 11 factors, we obtained a total score for the sites, which were then categorized as either having no human disturbance (0), low human disturbance (1–11), medium human disturbance (12–22) or high levels of human disturbance (23–33). Three sites were categorized as having no human disturbance, one had low disturbance and six had medium level human disturbance. A total of 9993 diatoms belonging to 40 genera were identified. The most abundant genera were Achnanthidium and Gomphonema, which made up 23.4 and 42.9% of the total diatom count, respectively. Achnanthidium dominated in remote areas with minimal human activities, while Gomphonema was more abundant in areas adjacent to increased human activities. The relative abundances of Achnanthidium, Denticula, Pinnularia, Rhopalodia and Stauroneis were negatively and significantly correlated, while that of Gomphonema was positively and significantly correlated to the human disturbance score (Spearman correlation, P 0.05), the lowest levels of these descriptors of community assemblage occurred at sites located near areas with relatively high human activities. The abundances of Achnanthes, Cymbella, Denticula, Encyonema and Pinnularia, Bacillaria and Mastogloia, Diatoma and Navicula and Eunotia and Mastogloia significantly decreased with increasing levels of total phosphorous, nitrate–nitrogen (N), ammonium–N and water turbidity, respectively (Spearman correlation, P < 0.05). Of the16 diatom index of biotic integrity (DIBI) metrics, 11 were significantly correlated with at least one of the environmental variables, while nine metrics were significantly correlated with the composite DIBI. Among the environmental variables the disturbance score was the only one that was significantly correlated with the DIBI. We conclude that although there is need for further work, periphytic diatoms associated with V. aethiopica may potentially be useful in assessing ecological conditions or the impact of human activities within the shallow marginal waters of Lake Kariba.

Whites and Water: How Euro-Africans Made Nature at Kariba Dam*

At Lake Kariba, conservation policies protect cultural heritage. In 1958, engineers created the lake by damming the Zambezi River. Over the next five years, the reservoir flooded 5,580 square km, displacing 57,000 Tonga farmers and destroying more habitat than any single human action ever had before. In response to this devastation, whites – particularly conservation-minded writers and photographers – expressed their shock and alarm. Gradually, however, they grew to accept the artificial lake, for the lake answered a deep European longing for water in inland, semi-arid Africa. Kariba Dam did the work of glaciers, carving intricate ‘fjords’ and ‘lochs’ in a country that previously lacked any shoreline at all. With Kariba, whites imported their hydrological heritage, and they found the lake to be beautiful. Writers soon called it ‘nature’ and advocated for its protection. Kariba thus exemplifies what has been until recently a hidden tension in ecological conservation: the tolerance – indeed, celebration – of history and cultural heritage. Until now, Euro-Zimbabwean heritage has benefited disproportionately from that tolerance.

Management challenges of freshwater fisheries in Africa

AbstractThe freshwater fisheries of Africa are important sources of income and protein for the people of the continent, and stocks of biodiversity for the world. This report discusses the experience for eight important lakes (Baringo, Chad, Kariba, Malawi, Naivasha, Nakuru, Tanganyika and Victoria), in order to provide an overview of the challenges facing the African freshwater systems, the interventions undertaken to manage the challenges, the inputs that have been required, and the lessons learned to guide further actions. In particular, the experience of the Global Environment Facility in promoting sustainable fisheries and lake basin management at five of these lakes (Baringo, Chad, Malawi, Tanganyika and Victoria) is discussed. The overall experience to date indicates a lack of effective management actions, as a result of limited accessibility and application of scientific information, poor dissemination of management information, inappropriate and un‐harmonized fishery laws and regulations, inadequate enforcement of existing laws and regulations, weak institutions and institutional processes, and inadequate funds for implementing fishery programmes.

The association between invertebrates and macrophytes in a tropical reservoir, Lake Kariba, Zimbabwe: a preliminary survey

The invertebrate fauna associated with aquatic macrophytes in the littoral of Lake Kariba was studied over a three-month period in 2002. Animals from seven classes — Hirudinea, Oligochaeta, Turbellaria, Insecta, Crustacea, Bivalvia and Gastropoda — were collected. Two hirudineans, Placobdella sp. and Haemopsis sp., and a turbellarian, Dugesia sp., were the most abundant taxa in the shoreline zone where Eichhornia crassipes was the most important macrophyte. The invertebrate community on other macrophytes was very different from that on Eichhornia, being dominated by gastropods and the shrimp Caridina nilotica. This community was similar to that found on macrophytes in Lake Kariba between 1964 and 1976, although the diversity of taxa was generally lower. The density of invertebrates was about four times higher at depths >1m, but the reasons for this are not known although it may reflect the relative abundance of macrophytes or the effects of wave action.

Size, diversity, dominance and trophic structures of the fish community in a tropical lake: a case study for the Sinazongwe area, Lake Kariba, Zambia

tropical : une etude de cas pour le secteur Sinazongwe, lac Kariba, en Zambie. Cette etude examine les structures en taille, diversite, dominance et trophiques de la communaute de poissons littoraux du secteur de Sinazongwe, lac Kariba, en Zambie, de 1980 a 1995. Elle est basee sur les donnees d'echantillonnage a l'aide de filets maillants et sur celles disponibles de la litterature. Les spectres de taille et de diversite ont, a l'instar de ceux des communautes de poissons demersaux marins exploites, des allures decroissantes regulieres : les effectifs et la diversite de poissons sont importants pour les petites tailles, et faibles pour les grandes tailles. Les spectres de tailles sont recurrents d'annee en annee et bien ajustes par des fonctions quadratiques. La diversite (indice de Shannon) et la dominance (indice de regularite, J') diminuent et augmentent lineairement avec la longueur du poisson. La diversite pour les grandes tailles diminue, selon les variations annuelles des pentes des spectres de diversite. Les courbes de comparaisons abondance et biomasse revelent des annees ou la communaute de poissons etait en « bonne sante », fortement et moderement perturbee. Les proportions de predateurs, en particulier de Hydrocynus vittatus, et le niveau trophique moyen diminuent lineairement d'annee en annee. Le spectre trophique moyen de diversite ne change pas. Les spectres trophiques moyens d'abondance et de biomasse montrent une communaute d'abord controlee par des animaux de hauts niveaux trophiques de 1980 a 1984, et inversement apres. Les descripteurs derives de la structure trophique detectent mieux les modifications subies par la communaute sous la pression de peche, et revelent pour la premiere fois pour le lac Kariba la baisse progressive du niveau trophique moyen au sein de la chaine alimentaire ciblee par la peche. Les indicateurs ecosystemiques etudiees s'averent des alternatives potentiellement prometteuses pour l'evaluation et la gestion des communautes de poissons exploitees dans des milieux aquatiques continentaux tropicaux.

Crocodile crimes: people versus wildlife and the politics of postcolonial conservation on Lake Kariba, Zimbabwe

This article is about the politics of conservation in postcolonial Southern Africa. It focuses on the process and consequences of redefining the Nile crocodile as an endangered species and explores the linked local and international, commercial and conservationist interests that allowed the animal to re-establish itself in state-protected waterways in colonial and postcolonial contexts. It investigates the effects of the animal’s successful re-accommodation by examining conflicts between crocodiles and the fishing communities sharing space on Lake Kariba, Zimbabwe. Fishermen’s hostile representations of the animal emphasize competition for fish, harassment, fear, loss of assets and loss of life. Their fear of crocodiles is heightened by the animal’s entanglement in local social life, through its association with witchcraft. The article emphasizes the importance of considering both hegemonic and marginalized ideas about animals in the light of the material interactions, relations of power and historical contexts that shape them. Understanding the attitudes and circumstances of the local communities who bear the physical and economic costs of living with dangerous animals is important––it threatens the future of conservation programmes and reveals the potential for significant abuses to accompany the conservation of wildlife in postcolonial contexts.

The feeding habits of Sargochromis Codringtonii in Lake Kariba, Zimbabwe

The food of adult Sargochromis codringtonii in Lake Kariba was dominated by prosobranch snails with pulmonate snails forming an insignificant dietary component. S. codringtonii does not show particular preference for any snail species, feeding on those species that are readily available. Morphometrical analysis of the feeding structures of S. codringtonii showed that the fish is well adapted to handling a molluscivorous diet. The pharyngeal jaws with their flat crowned teeth are well adapted to crushing molluscs. The daily food consumption rate of S. codringtonii was estimated over different seasons. Estimates of food consumption indicate that the fish consumed 13.96% of their dry body weight per day in summer falling to 4.46% in winter. The low consumption of pulmonate snails suggests that S. codringtonii can not be a successful biological control agent against the vectors of schistosomiasis.

Prosobranch mollusc species- and size-preferences of Sargochromis codringtonii (Cichlidae) in Lake Kariba, Zimbabwe

From the stomach contents of 28 wild-caught Sargochromis codringtonii from Lake Kariba the size and species of snails consumed were estimated from opercula found. An energetic cost/benefit ratio of the various sizes of the most frequent prey, Bellamya capillata, was calculated. The size of snails consumed increased significantly with fish size, with large fish showing individual size preferences. Ingested snails were of sizes with relatively low energetic cost/benefit ratios.

Aspects of the feeding ecology of Sargochromis codringtonii in Lake Kariba, Zimbabwe

Abstract Sargochromis codringtonii has always been considered a good candidate for the biological control of snails. However, there is lack of data on the feeding ecology of this species. The diet of S. codringtonii was examined by an analysis of stomach contents. The food of adult S. codringtonii in Lake Kariba is dominated by prosobranch snails. Pulmonate snails form a small insignificant component of the diet of S. codringtonii , and the reasons for this are discussed. Electivity indices were used to investigate prey selection. S. codringtonii does not show a particular preference for any snail species. It feeds on any snail species that is readily available. A morphometrical analysis of the feeding structures of S. codringtonii showed that the fish is well adapted to handling a molluscivorous diet. The daily food consumption of S. codringtonii was estimated over different seasons using the Elliot &amp; Persson (1978 ) model [ J. Anim. Ecol.47.977–991]. Estimates of food consumption indicate that the fish consumed 14.0% of their dry body weight per day in summer and this falls to 4.5% in winter. The low consumption of pulmonates means that S. codringtonii cannot be a successful biological control agent against the vectors of schistosomiasis.

Laboratory experiments on snail-size selection by a snail predator, Sargochromis codringtoni (Pisces: Cichlidae).

The cichlid fish, Sargochromis codringtoni, is a known snail predator 1‐3 and has shown some promise in snail-control. 4,5 However, some experiments showed that the fish failed to control the largest sizes of Bulinus globosus and preferred the smaller B. tropicus, which is not an intermediate host for S. haematobium. 6 Obviously, this apparent preference for B. tropicus may not be entirely a question of snail size since, for example, palatability of the two species could be involved. However, from a snail control point of view, snail-size selection by a potential predator is important because within a snail population, larger specimens seem to be more important for transmission than smaller specimens, due to a higher rate of cercarial shedding 7,8 and higher infection rates. 9,10 Consumption of large specimens of snails might depend on the size/age of the predator. This, in turn, raises some practical considerations in terms of propagation of the predator. The diet of S. codringtoni in natural systems has been investigated on several occasions, 2,11,12 but with different conclusions. It appears that diet is influenced by both habitat and fish size. For other molluscivores, varying degrees of preference for specific snail sizes have been demonstrated, 13‐15 but there is only limited knowledge about snail size selection of S. codringtoni. In this study, we investigated the preference of S. codringtoni for prey comprising B. globosus of different sizes in aquaria. A substratum of sand, to a depth of 3 cm was placed in seven large aquaria (L, 100 cm; W, 60 cm; H, 60 cm). Tap water (currently used routinely for snail culture in this laboratory) was added to 2/3 capacity (240 l) and was left to de-chlorinate over night. The following day, Bulinus globosus of six different size-classes (shell height, 4‐5.9, 6‐7.9, 8‐9.9, 10‐11.9, 12‐13.9, and 14‐16 mm) were introduced into the aquaria together with plants, which included 2 m of Lagarosiphon major strands and 40 g (wet-weight) of Najas pectinata. The number of snails introduced varied between size classes and slightly between repeat experiments due to variation in availability. For the classes 4‐5.9 mm; 8‐9.9 mm and 14‐16 mm, 10 snails were introduced, while for the class 10‐11.9 mm, 25 snails were used. For the classes 6‐7.9 mm and 12‐13.9 mm, 20 and 25 snails were introduced, respectively, in the first repeat. These numbers were, however, lowered to 15 and 20, respectively, in the second and third repeat. The largest snails (8‐16 mm) were wild caught, while the smallest snails (4‐7.9 mm) were laboratory-bred. The only source of light was the sunlight that entered through the windows in the laboratory (dark-period: 8 h 53 min). The fish used in the experiment were caught in Lake Kariba using hook and line, and driven to De Beers Research Laboratory in Chiredzi, Zimbabwe, where they were kept in earth ponds for 32 days prior to the initiation of the experiments. Between repeat experiments the fish were kept in one aquarium. The following day, one S. codringtoni was introduced into each of six aquaria, while the last aquarium was left without fish and served as a control. Before introduction, the fish were

Snail-parasite compatibility and prevalence of Schistosoma haematobium on the shores of Lake Kariba, Zambia.

Reduced snail-parasite compatibility might be at least partially responsible for the decrease observed, over the last three decades, in the prevalence of urinary schistosomiasis on the shores of Lake Kariba, Zambia. To explore this possibility, the prevalences of urinary schistosomiasis in schoolchildren were investigated in three disparate areas of Zambia (Lake Kariba, Lake Bangweulu and Lusaka), and attempts were made to infect the snails that developed from the eggs of snails collected from each of these sites with Schistosoma haematobium from each of the sites. The prevalence of S. haematobium infection in schoolchildren ranged from 0% around Lake Bangweulu to 76% around Lake Kariba. The F1 progeny of Siavonga (Lake Kariba) snails showed good compatibility with the local parasite but were also susceptible to all of the geographical strains of S. haematobium tested. The interaction between the S. haematobium and S. mansoni found along the shores of Lake Kariba may favour S. mansoni, since prevalences of urinary schistosomiasis tend to be relatively high where S. mansoni is absent. Although Lake Bangweulu was confirmed to be an area of very low endemicity for urinary schistosomiasis, the snails bred from snails collected in this area were compatible with isolates of S. haematobium from the same region and also those from the other regions. In general, sympatric snail-parasite combinations were the most successful. All the snails were identified as Bulinus globosus, on the basis of common enzyme profiles, although polymorphism was evident for malate dehydrogenase (MDH): two samples had type-1 MDH and the rest were of type 3. Isoenzyme patterns for both acid phosphatase (AcP) and MDH could be used to distinguish between infected and uninfected snails.

Water quality of the Eastern Basin of Lake Kariba, Zimbabwe in relation to the encroachment of Eichhornia crassipes

(2001). Water quality of the Eastern Basin of Lake Kariba, Zimbabwe in relation to the encroachment of Eichhornia crassipes. SIL Proceedings, 1922-2010: Vol. 27, No. 6, pp. 3595-3598.

Factors affecting density‐independent survival of an island population of tsetse flies in Zimbabwe

AbstractAnalysis is presented of the factors affecting survival probability in populations of tsetse flies Glossina morsitans morsitans Westwood and G. pallidipes Austen (Diptera: Glossinidae) on Antelope Island, Lake Kariba, Zimbabwe. For mature male and female adult G. m. morsitans mean temperature (Tbar) accounted for 70 and 50%, respectively, of the variance in mark‐recapture estimates of survival when the flies were not subjected to trapping. Saturation deficit (SD) only accounted for 36 and 33%, respectively. Maximum temperature (Tmax) and SD accounted for 36–42% of the variance in male and female G. pallidipes. For the corresponding Moran curve estimates of the survival over all developmental stages, SD lagged by three weeks accounted for 61 and 41% of the variance for male and female G. m. morsitans, respectively, and 64 and 56% for G. pallidipes. The corresponding figures for plots against Tmax were 44, 23, 23, and 21%, respectively. The same patterns were seen in the whole data set once allowance was made for the effect of trapping on survival and for an effect of season, correlated with an index of photosynthetic activity. For male G. m. morsitans there was a significant effect of saturation deficit, but not temperature, on immature survival. Decreased adult survival at high temperatures results from the need to feed more frequently and hence to take more risks per unit time. High saturation deficits result directly in reduced emergence of healthy flies from pupae.

Potential Effects of Beauveria bassiana (Balsmo) Vuillemin on Neochetina bruchi Hustache (Coleoptera: Curculionidae), a Biological Control Agent of Water Hyacinth

Abstract The potential effects of Beauveria bassiana, an entomopathogen, on the biological control agent of water hyacinth, Neochetina bruchi, were assessed. In bioassays, B. bassiana induced mortality of the eggs, larvae, and adults when the N. bruchi stages were either sprayed or dipped in conidia concentrations of 5 × 105, 5 × 106, 5 × 107, 5 × 108, and 5 × 109 conidia/ml. The fungus caused highest mortality in larvae, whereas eggs were most resistant. Mortality increased in all insect stages as the conidia concentrations increased. The LT50 values of the pathogen on eggs at 5 × 108 and 5 × 109 conidia/ml were 10 and 7.2 days, respectively. For larvae and adults, the LT50 values at 5 × 109 conidia/ml were 3.6 and 6 days, respectively. The LC50 values were significantly different for all three stages at day 12 posttreatment, with the values of 9.5 × 107, 7.6 × 105, and 8.9 × 106 conidia/ml for eggs, larvae, and adults, respectively. The prevalence of B. bassiana in adult N. bruchi was measured at three water bodies in Zimbabwe. The prevalence of B. bassiana was highest in February–March of 2000. At Lake Chivero, the maximum reached 38%, whereas it was much lower at Lake Kariba and at Kudzwe Dam. Differences in the prevalence of B. bassiana appeared to be coupled with herbicide sprays used for the control of the water hyacinth problem. The prevalence was highest at sites where herbicides were used regularly and lowest where no herbicides were used. The temperatures at Lake Chivero were lower than those at the two other sites and this difference may have influenced the level of B. bassiana prevalence in N. bruchi.

The effect of temperature and saturation deficit on mortality in populations of male Glossina m. morsitans (Diptera: Glossinidae) in Zimbabwe and Tanzania.

The methods of Bailey and of Jolly and Seber were used to provide maximum likelihood estimates of population parameters for Jackson's classical mark-recapture experiments on males of the tsetse fly Glossina m. morsitans Westwood. These were compared with Jolly-Seber (J-S) estimates for the same fly from more recent work on Antelope Island, Lake Kariba, Zimbabwe. The Bailey estimates of birth and death rates and total population size had markedly lower variances than Jackson's originals. Both sets of estimates provided moving averages over 6-week periods, whereas the Jolly-Seber analysis provided independent weekly estimates and their variance is consequently higher. Saturation deficit and maximum temperature (Tmax) accounted for 11 and 16% respectively of the variance in independent 4-week means of the weekly J-S survival probabilities. Analysis of covariance, carried out on a joint data set of smoothed J-S estimates of the survival probability in Tanzania and Zimbabwe, showed a significant effect of Tmax on survival. When this effect was removed, the survival probability in the Tanzania studies was found to be 8% lower than on Antelope Island. The two effects accounted for 50% of the variance in the joint data. When saturation deficit was substituted for Tmax, regression only accounted for 35% of the variance. If saturation deficit is important in determining tsetse survival, it must act on stages other than the post-teneral adult. Given the continuous increase in mortality, even at moderate temperatures, it is hard to envisage a direct effect of Tmax. There may be an indirect effect, however, via the number of hunger-related deaths resulting from the increase in the feeding rate with increasing temperature.

The zooplankton community of Lake Kariba in 1962/63 following impoundment of the Zambezi River

Lake Kariba, bordered by Zambia in the north and Zimbabwe in the south, was formed following the impoundment of the the Zambezi River in 1955. Pre- and post-impoundment studies, which were undertaken on Lake Kariba by the Joint Fisheries Research Organisation of Zambia and Malawi, generated data on the limnology, fish and zooplankton. Fryer identified free-living Crustacea from the flooded backwaters of the Zambezi river. Thomasson, reporting on the algae in the lake, identified zooplankton collected during May and June 1959. This paper coordinates information on the lake basins, the rivers flowing into Lake Kariba, sampling stations and identification of the zooplankton collected in more comprehensive surveys in 1962 and 1963. At this time the zooplankton community in the lake was made up of thermophilic species adapted to survival in the water column. However, some calanoid copepod species were collected, mainly from river estuaries and in shallow areas of the lake, which are related more to their natural habitat. The zooplankton community comprised 10 rotifer species, 16 species of Cladocera, six calanoid and at least six cyclopoid copepod species, three ostracod species, the limnomedusa Limnocnida tanganjicae, a species of Chaoborus, and a few insect larvae. In less than a decade after impoundment of the Zambezi River, the large subtropical Lake Kariba was colonised successfully by a diverse zooplankton community.

Spatial and temporal variations in the food of the sardine Limnothrissa miodon (Boulenger, 1906) in Lake Kariba, Zimbabwe

Spatial and temporal variations in the food of the Lake Tanganyika sardine, Limnothrissa miodon, locally called “kapenta”, are assessed on the basis of stomach content analysis at three sites using the percentage frequency of occurrence method. More than 27 different types of organisms were found in the stomachs. Crustaceans dominated, with the small cladoceran, Bosmina longirostris most important. Daphnia lumholtzi, Diaphanosoma excisum and calanoids occurred in the stomachs more at the site which was richer in nutrients. Insects were present most frequently at sites closest to the shore. The diet was influenced by lake turnover, the rainy season, and sampling site.

The relationship of temperature and hydrological factors to catch per unit effort, condition and size of the freshwater sardine, Limnothrissa miodon (Boulenger), in Lake Kariba

The relationships between catch per unit effect (Cpue), condition factor and mean length of the fresh water sardine Limnothrissa miodon and air temperature, as well as three hydrological factors, rainfall, river inflow and the water level in Lake Kariba, were determined by regression and correlation analysis of time series data for the period between 1970 and 1996. The aim was to test the predictive value of the environmental variables and to obtain models that describe the relationships between catches and environmental factors. All environmental variables had a significant relation with Cpue and condition, but the relations of the environmental variables to mean length were weak and mostly insignificant. When using data for the whole time period, the maximum temperature was the best predictor of Cpue. Of the hydrological factors, total river inflow had the highest regression coefficient. The data were split into two 11-year periods (1975–1985 and 1986–1996) in order to test the predictor models. Except for the Zambezi river inflow variable, estimates of Cpue for 1986–1996 using the 1975–1985 model were not significantly different from the observed Cpue. Cross-correlation showed a 5–7 year half cycle in the trend of catches, temperature and the hydrological factors that may be useful for Cpue forecasts.