ABSTRACT A comparison between historical and current data was done to determine whether the conce... more ABSTRACT A comparison between historical and current data was done to determine whether the concentrations of total phosphorus, orthophosphate and chlorophyll a, and Secchi disc transparency, have changed in the Sanyati Basin of Lake Kariba following the commencement of cage culture of fish in 1998. Total phosphorus concentration is markedly elevated in comparison to historical offshore data, while offshore orthophosphate concentration is lower than when the lake was eutrophic. Chlorophyll a concentrations were similar to the mean value of 4 μg l–1 reported from open water, but lower than the mean of 22 μg l–1 reported from inshore waters. Current values of Secchi disc transparency are lower than the historical records. To date, cage aquaculture seems not to have changed the trophic status of Sanyati Basin, and any nutrient enrichment it caused may have been mitigated by nutrient losses, through both outflow at the dam and fish harvesting.
Mashoko Dam is in Ago-ecological Region 4 in Zimbabwe. Five sampling sites were randomly selected... more Mashoko Dam is in Ago-ecological Region 4 in Zimbabwe. Five sampling sites were randomly selected and each site was sampled twice per month, for six months. A total of 180 Oreochromis mossambicus fish (101 females and 79 males) were caught. The fish were examined for Clinostomum metacercariae by cutting the ventral side from the anal opening to the lower jaw. The gill chambers were examined and inspected visually to detect macroscopic parasites. Of the 180 fish collected during the study, 113 (62.8%) were infected by 284 Clinostomum larvae in the cranial cavity while 67 fish were not infected. Among the infected fish, 46 were males and 67 were females. Greater parasite burden and mean intensity were observed in female fish (2.7 MI) than males (2.2 MI). There was no statistically significant difference in mean intensity of infection between male and female fish (n=180; t=0.521; p<0.05). Uninfected fish were in a poorer condition than infected fish in July and October only. The low...
One of the defining characteristics of inland fisheries is that they are closely impacted by othe... more One of the defining characteristics of inland fisheries is that they are closely impacted by other essential human activities that rely on the same fresh or brackish water ecosystems, such as hydroelectricity generation and irrigated agriculture. Starting with the premise that an understanding of fisheries' interactions with these external sectors is in itself critical for achieving sustainability of the fisheries, this paper explores the topic of intersectoral governance and outlines an approach to analyzing the intricate and often challenging sector relationships. By drawing on examples of inland fisheries from around the world, the paper proposes four broad discursive mechanisms that can structure the study of the intersectoral dynamics, i.e., system characterization, valuation, power relations, and vertical policy interaction. A synthesis model then demonstrates their interwoven nature, revealing the way each mechanism influences one another as together they shape overall ou...
Hydroacoustic surveys were carried out on Lake Kariba using predetermined transects in order to d... more Hydroacoustic surveys were carried out on Lake Kariba using predetermined transects in order to determine the abundance of the freshwater sardine, Limnothrissa miodon. The surveys covered four of the lake's five hydrological basins. The spatial distribution of the kapenta was heterogenous. Marked inter-transect variations were observed. Mean densities for individual transects varied from 8 700 fish per hectare in June 1994 to 74 000 fish per hectare in February 1995. Variations within transects were also high. Mean fish densities for the whole lake varied from 27 000 fish per hectare in July 1994 to 48 000 fish per hectare in February 1995. The densities observed by earlier workers were within the range observed in this study. Preliminary estimates of the biomass were also obtained. Biomass estimates from previous studies were within the range observed in this study
ABSTRACT A comparison between historical and current data was done to determine whether the conce... more ABSTRACT A comparison between historical and current data was done to determine whether the concentrations of total phosphorus, orthophosphate and chlorophyll a, and Secchi disc transparency, have changed in the Sanyati Basin of Lake Kariba following the commencement of cage culture of fish in 1998. Total phosphorus concentration is markedly elevated in comparison to historical offshore data, while offshore orthophosphate concentration is lower than when the lake was eutrophic. Chlorophyll a concentrations were similar to the mean value of 4 μg l–1 reported from open water, but lower than the mean of 22 μg l–1 reported from inshore waters. Current values of Secchi disc transparency are lower than the historical records. To date, cage aquaculture seems not to have changed the trophic status of Sanyati Basin, and any nutrient enrichment it caused may have been mitigated by nutrient losses, through both outflow at the dam and fish harvesting.
Mashoko Dam is in Ago-ecological Region 4 in Zimbabwe. Five sampling sites were randomly selected... more Mashoko Dam is in Ago-ecological Region 4 in Zimbabwe. Five sampling sites were randomly selected and each site was sampled twice per month, for six months. A total of 180 Oreochromis mossambicus fish (101 females and 79 males) were caught. The fish were examined for Clinostomum metacercariae by cutting the ventral side from the anal opening to the lower jaw. The gill chambers were examined and inspected visually to detect macroscopic parasites. Of the 180 fish collected during the study, 113 (62.8%) were infected by 284 Clinostomum larvae in the cranial cavity while 67 fish were not infected. Among the infected fish, 46 were males and 67 were females. Greater parasite burden and mean intensity were observed in female fish (2.7 MI) than males (2.2 MI). There was no statistically significant difference in mean intensity of infection between male and female fish (n=180; t=0.521; p<0.05). Uninfected fish were in a poorer condition than infected fish in July and October only. The low...
One of the defining characteristics of inland fisheries is that they are closely impacted by othe... more One of the defining characteristics of inland fisheries is that they are closely impacted by other essential human activities that rely on the same fresh or brackish water ecosystems, such as hydroelectricity generation and irrigated agriculture. Starting with the premise that an understanding of fisheries' interactions with these external sectors is in itself critical for achieving sustainability of the fisheries, this paper explores the topic of intersectoral governance and outlines an approach to analyzing the intricate and often challenging sector relationships. By drawing on examples of inland fisheries from around the world, the paper proposes four broad discursive mechanisms that can structure the study of the intersectoral dynamics, i.e., system characterization, valuation, power relations, and vertical policy interaction. A synthesis model then demonstrates their interwoven nature, revealing the way each mechanism influences one another as together they shape overall ou...
Hydroacoustic surveys were carried out on Lake Kariba using predetermined transects in order to d... more Hydroacoustic surveys were carried out on Lake Kariba using predetermined transects in order to determine the abundance of the freshwater sardine, Limnothrissa miodon. The surveys covered four of the lake's five hydrological basins. The spatial distribution of the kapenta was heterogenous. Marked inter-transect variations were observed. Mean densities for individual transects varied from 8 700 fish per hectare in June 1994 to 74 000 fish per hectare in February 1995. Variations within transects were also high. Mean fish densities for the whole lake varied from 27 000 fish per hectare in July 1994 to 48 000 fish per hectare in February 1995. The densities observed by earlier workers were within the range observed in this study. Preliminary estimates of the biomass were also obtained. Biomass estimates from previous studies were within the range observed in this study
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