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Okello W.,National Fisheries Resources Research Institute NaFIRRI | Kurmayer R.,Austrian Academy of Sciences
Lakes and Reservoirs: Research and Management | Year: 2011

This study investigated the seasonal development of phytoplankton and potential microcystin (MC)-producing cyanobacteria and MC concentrations in freshwater lakes in Uganda. During 1year (May 2007-April 2008), monthly measurements were made of chemical and physical characteristics, phytoplankton composition and MC concentrations in a hypertrophic crater lake (Lake Saka), in shallow eutrophic lakes (Lakes Mburo, George and Edward) and in Lake Victoria (Murchison Bay, Napoleon Gulf). Throughout the study period, cyanobacteria (composed of the genera Anabaena, Aphanocapsa, Chroococcus, Cylindrospermopsis, Microcystis, Planktolyngbya and Planktothrix) dominated, always contributing >50% to the total phytoplankton biovolume. All samples from all sampling sites were found to contain MC. Samples from Lake Saka had the maximum MC concentration (10μgL-1) in July 2007. The minimum concentration (0.02μgL-1) was recorded in Lake George for the months of May and June 2007 and January and April, 2008. Intermediate MC concentrations (0.1-2.5μg MC-LR eq.L-1) were observed at all the sampling sites in the other three lakes. Highly significant positive linear relationships between the total MC concentration and Microcystis cell numbers were observed for all sampling sites. Relating the total MC concentrations to Microcystis cells revealed a >100-fold variation in the average MC contents per cell between lakes. While Microcystis from Lake George exhibited the lowest MC cell quotas (0.03-1.24fgcell-1), Microcystis from Lake Saka consistently exhibited maximum MC cell contents (14-144fgcell-1). It was concluded that MC production was because of the occurrence of Microcystis at all sampling sites. The populations differed consistently between sites and independent of the season in their average MC content per cell. © 2011 The Authors. Journal compilation © 2011 Blackwell Publishing Asia Pty Ltd.


Arinaitwe K.,Makerere University | Rose N.L.,University College London | Muir D.C.G.,Environment Canada | Kiremire B.T.,Makerere University | And 2 more authors.
Chemosphere | Year: 2016

Information on historical deposition of persistent organic pollutants (POPs) for African lakes is very limited. We investigated historical deposition trends and sources of POPs in sediment cores from Lakes Victoria (SC1), Bujuku (Buju2) and Mahoma (Maho2). The latter two lakes are situated in the Rwenzori mountain range in western Uganda. SC1 was taken from a central depositional area within the Ugandan part of the lake. Profiles in Buju2 and Maho2 were used as a reference for historical atmospheric deposition. For the post-1940 sediment deposits in SC1, average focusing factor-adjusted fluxes (FFFs) of σDDTs, polychlorinated biphenyls (σPCBs), hexachlorocyclohexanes (σHCHs) and chlordanes (σCHLs) were 390, 230, 210 and 120 ng m-2 yr-1. Higher fluxes of σDDTs, σPCBs, and σCHLs were observed in Buju2 and Maho2. The average FFF of HCB in Buju2 was the highest while the values for Maho2 and SC1 were similar. The endosulfan FFFs in SC1 were lower than in the alpine lake cores. Generally, Buju2 was a better reference for historical atmospheric deposition of POPs than Maho2 probably due to distortion of the latter's profile by Lake Mahoma's forested catchment. Profiles of p,p'-DDE, σCHLs and HCB in SC1 were consistent with atmospheric deposition while profiles of PCBs and HCHs were indicative of particle-bound loadings from additional sources. Profiles of endosulfans, DDTs, and chlordanes were consistent with influence of other factors such as anoxia, and dilution. Further studies of spatial resolution of historical deposition, especially in near-shore deposition areas of the lake are recommended. © 2015 Elsevier Ltd.


Sharpe D.M.T.,McGill University | Wandera S.B.,National Fisheries Resources Research Institute NaFIRRI | Chapman L.J.,McGill University
Evolutionary Applications | Year: 2012

Fishing and introduced species are among the most important stressors affecting freshwaters and can also be strong selective agents. We examined the combined effects of commercial fishing and an introduced predator (Nile perch, Lates niloticus) on life history traits in an African cyprinid fish (Rastrineobola argentea) native to the Lake Victoria basin in East Africa. To understand whether these two stressors have driven shifts in life history traits of R. argentea, we tested for associations between life history phenotypes and the presence/absence of stressors both spatially (across 10 Ugandan lakes) and temporally (over four decades in Lake Victoria). Overall, introduced Nile perch and fishing tended to be associated with a suite of life history responses in R. argentea, including: decreased body size, maturation at smaller sizes, and increased reproductive effort (larger eggs; and higher relative fecundity, clutch volume, and ovary weight). This is one of the first well-documented examples of fisheries-induced phenotypic change in a tropical, freshwater stock; the magnitude of which raises some concerns for the long-term sustainability of this fishery, now the most important (by mass) in Lake Victoria. © 2012 Blackwell Publishing Ltd.


Everson I.,Anglia Ruskin University | Kayanda R.,Tanzania Fisheries Research Institute | Taabu-Munyaho A.,National Fisheries Resources Research Institute NaFIRRI
Lakes and Reservoirs: Research and Management | Year: 2013

Time series, using different echosounders or large-scale multiship acoustic surveys, can be criticized because equipment changes might affect the final results. This criticism was addressed previously by comparing the results from different vessels using echo integration on the target species. The acoustically estimated standing stock of Nile perch (Lates niloticus) in Lake Victoria, East Africa, declined to 50% between successive surveys six months apart in 2007, prompting the criticism that a change in echosounder was responsible for this observation. This concern has been addressed, using data from the same four small localities around the lake, Emin Pasha Gulf, Nyanza Gulf, Speke Gulf and the vicinity of the Sesse Islands, from six surveys, spanning the time when the change in echosounder occurred. For three of the locations, echo integration and single target detections within the first bottom echo indicated no significant differences in echosounder performance. Results from the fourth location, Sesse Islands, showed very low backscatter, possibly due to a layer of detritus on the lake bed. It is concluded that all data are equally comparable, providing echosounders are correctly calibrated with the vessel being stationary, although there may still be differences under operational conditions. Characteristics of intercalibration sites are discussed in this study. The results also show changes in substrate, likely attributable to local environmental changes between surveys. © 2013 Wiley Publishing Asia Pty Ltd.


Okello W.,Austrian Academy of Sciences | Okello W.,National Fisheries Resources Research Institute NaFIRRI | Ostermaier V.,Austrian Academy of Sciences | Portmann C.,Ecole Polytechnique Federale de Lausanne | And 2 more authors.
Water Research | Year: 2010

It is generally agreed that the hepatotoxic microcystins (MCs) are the most abundant toxins produced by cyanobacteria in freshwater. In various freshwater lakes in East Africa MC-producing Microcystis has been reported to dominate the phytoplankton, however the regulation of MC production is poorly understood. From May 2007 to April 2008 the Microcystis abundance, the absolute and relative abundance of the mcyB genotype indicative of MC production and the MC concentrations were recorded monthly in five freshwater lakes in Uganda: (1) in a crater lake (Lake Saka), (2) in three shallow lakes (Lake Mburo, George, Edward), (3) in Lake Victoria (Murchison Bay, Napoleon Gulf). During the whole study period Microcystis was abundant or dominated the phytoplankton. In all samples mcyB-containing cells of Microcystis were found and on average comprised 20 ± 2% (SE) of the total population. The proportion of the mcyB genotype differed significantly between the sampling sites, and while the highest mcyB proportions were recorded in Lake Saka (37 ± 3%), the lowest proportion was recorded in Lake George (1.4 ± 0.2%). Consequently Microcystis from Lake George had the lowest MC cell quotas (0.03-1.24 fg MC cell-1) and resulted in the lowest MC concentrations (0-0.5 μg L-1) while Microcystis from Lake Saka consistently showed maximum MC cell quotas (14-144 fg cell-1) and the highest MC concentrations (0.5-10.2 μg L-1). Over the whole study period the average MC content per Microcystis cell depended linearly on the proportion of the mcyB genotype of Microcystis. It is concluded that Microcystis populations differ consistently and independently of the season in mcyB genotype proportion between lakes resulting in population-specific differences in the average MC content per cell. © 2010 Elsevier Ltd. All rights reserved.


Okello W.,Austrian Academy of Sciences | Okello W.,National Fisheries Resources Research Institute NaFIRRI | Portmann C.,Ecole Polytechnique Federale de Lausanne | Erhard M.,AnagnosTec. GmbH | And 2 more authors.
Environmental Toxicology | Year: 2010

Microcystins (MCs) are cyclic heptapeptides, which are the most abundant toxins produced by cyanobacteria in freshwater. The phytoplankton of many freshwater lakes in Eastern Africa is dominated by cyanobacteria. Less is known, however, on the occurrence of MC producers and the production of MCs. Twelve Ugandan freshwater habitats ranging from mesotrophic to hypertrophic conditions were sampled in May and June of 2004 and April of 2008 and were analyzed for their physicochemical parameters, phytoplankton composition, and MC concentrations. Among the group of the potential MC-producing cyanobacteria, Anabaena (0-107 cells ml-1) and Microcystis (10 3-107 cells ml-1) occurred most frequently and dominated in eutrophic systems. A significant linear relationship (n = 31, r2 = 0.38, P < 0.001) between the Microcystis cell numbers and MC concentration (1.3-93 fg of MC cell-1) was observed. Besides [MeAsp3, Mdha7]-MC-RR, two new MCs, [Asp 3]-MC-RY and [MeAsp3]-MC-RY, were isolated and their constitution was assigned by LC-MS2. To identify the MC-producing organism in the water samples, (i) the conserved aminotransferase domain part of the mcyE gene that is indicative of MC production was amplified by general primers and cloned and sequenced, and (ii) genus-specific primers were used to amplify the mcyE gene of the genera Microcystis, Anabaena, and Planktothrix. Only mcyE genotypes that are indicative of Microcystis sp. were obtained via the environmental cloning approach (337 bp, 96.1-96.7% similarity to the Microcystis aeruginosa strain PCC7806). Accordingly, only the mcyE primers, which are specific for Microcystis, revealed PCR products. We concluded that Microcystis is the major MC-producer in Ugandan freshwater. © 2009 Wiley Periodicals, Inc.


Everson I.,Anglia Ruskin University | Taabu-Munyaho A.,National Fisheries Resources Research Institute NaFIRRI | Kayanda R.,Tanzania Fisheries Research Institute
Fisheries Research | Year: 2013

Data from the first series of lakewide fisheries acoustic surveys of Lake Victoria, East Africa, have been re-analysed according to current protocols. Surveys took place in February and August each year between 1999 and 2002. The primary aim has been to estimate the standing stock of Nile perch and dagaa, the main species taken in commercial fisheries on the lake. The results show that over the period of the surveys from 1999 to 2002 there was no significant trend in the standing stock of either species with time although there was a significant seasonal effect higher values in February as compared to August. Information from bottom trawls during the surveys supports these conclusions. The results have been considered in the context of a food web from which it is concluded that in order for sufficient food to be present for the Nile perch there must be a significant proportion of the decapod crustacean Caridina present. It is noted that this species can be estimated acoustically using multifrequency echosounders but is very difficult with the single frequency system used on the 1999-2002 surveys. Refinements in the methodology will permit the simultaneous assessment of several key components in the food web and open the way to effective ecosystem-based fisheries management. © 2012.


Wanda F.M.,National Fisheries Resources Research Institute NaFIRRI | Namukose M.,National Fisheries Resources Research Institute NaFIRRI | Matuha M.,National Fisheries Resources Research Institute NaFIRRI
African Journal of Aquatic Science | Year: 2015

Water hyacinth invaded Lake Victoria in the 1980s and, by 1998, had attained peak coverage of approximately 2 000 ha in the Ugandan waters of the lake. Control interventions, especially via biological means, significantly reduced the weed's coverage to non-nuisance levels (<10 ha) by 1999. Although resurgence was noticed in 2001, total coverage never reached the infestation levels attained between 1994 and 1998. By March 2012, infestations still occurred in hotspot bays, including MacDonald (52.1 ha, SE 3.0), Fielding (38.0 ha, SE 1.4), Bunjako (33.7 ha, SE 1.9), Murchison (17.1 ha, SE 0.9), Lwera (8.5 ha, SE 0.3), Napoleon Gulf (2.9 ha, SE 0.3) and Berkeley (2.1 ha, SE 0.1), in addition to some bays of the Ssesse Islands (47.8 ha, SE 0.5) and on the Kagera River. These hotspots were characterised by shelter from offshore winds and ample macronutrients (NO3-N > 13.8 µg l−1, SE 1.6; SRP > 17.2 µg l−1, SE 3.2) in the water column. Control efforts, mainly the use of biological control agents on a large scale, manual and mechanical removal at strategic sites, plus a reduction in nutrient loading, should therefore target the identified hotspot bays of the lake. © 2015, Copyright © NISC (Pty) Ltd.


Ogutu-Ohwayo R.,National Fisheries Resources Research Institute NaFIRRI | Natugonza V.,National Fisheries Resources Research Institute NaFIRRI | Musinguzi L.,National Fisheries Resources Research Institute NaFIRRI | Olokotum M.,National Fisheries Resources Research Institute NaFIRRI | Naigaga S.,National Fisheries Resources Research Institute NaFIRRI
Journal of Great Lakes Research | Year: 2016

Inland fisheries are important for nutrition, employment, and income, but climate variability and change are adding to other stressors, such as overexploitation, pollution, habitat degradation, and invasive species, to threaten their productivity as well as livelihoods of fisheries-dependent communities. Understanding the whole socio-ecological system to enable communities to adapt and build resilience is therefore vital. Here, we present results from a review of the responses of African lakes, fisheries productivity, and livelihoods to climate variability and change, and provide suggestions on required policy interventions to promote adaptation and build resilience. Changes in climate variables, especially temperature, wind speed, and rainfall have contributed to changes in lake water levels, loading, and recycling of nutrients. In some lakes, such disruptions in physical and chemical conditions have triggered changes in water quality, algae and invertebrate productivity, life history of fish, and contributed to shifts in fish community composition, proliferation of invasive aquatic weeds, and changes in parasite-vector-host interactions. Fish yield has either increased or decreased depending on climatic events, with the latter negatively affecting livelihoods, and forcing affected communities to adapt. Because adaptation strategies are location specific, and influenced by local conditions, many adaptation strategies have been unguided and have negatively affected fisheries. The responses of fisheries to climate change vary among lakes of different morphometric characteristics. There is need for consistent data to examine the direction and consequences of climate variability and change on fisheries and livelihoods of specific aquatic systems, and promote location specific adaptation and mitigation measures. © 2016 International Association for Great Lakes Research.


PubMed | Environment Canada, National Fisheries Resources Research Institute NaFIRRI, Makerere University and University College London
Type: | Journal: Chemosphere | Year: 2015

Information on historical deposition of persistent organic pollutants (POPs) for African lakes is very limited. We investigated historical deposition trends and sources of POPs in sediment cores from Lakes Victoria (SC1), Bujuku (Buju2) and Mahoma (Maho2). The latter two lakes are situated in the Rwenzori mountain range in western Uganda. SC1 was taken from a central depositional area within the Ugandan part of the lake. Profiles in Buju2 and Maho2 were used as a reference for historical atmospheric deposition. For the post-1940 sediment deposits in SC1, average focusing factor-adjusted fluxes (FFFs) of DDTs, polychlorinated biphenyls (PCBs), hexachlorocyclohexanes (HCHs) and chlordanes (CHLs) were 390, 230, 210 and 120 ng m(-2) yr(-1). Higher fluxes of DDTs, PCBs, and CHLs were observed in Buju2 and Maho2. The average FFF of HCB in Buju2 was the highest while the values for Maho2 and SC1 were similar. The endosulfan FFFs in SC1 were lower than in the alpine lake cores. Generally, Buju2 was a better reference for historical atmospheric deposition of POPs than Maho2 probably due to distortion of the latters profile by Lake Mahomas forested catchment. Profiles of p,p-DDE, CHLs and HCB in SC1 were consistent with atmospheric deposition while profiles of PCBs and HCHs were indicative of particle-bound loadings from additional sources. Profiles of endosulfans, DDTs, and chlordanes were consistent with influence of other factors such as anoxia, and dilution. Further studies of spatial resolution of historical deposition, especially in near-shore deposition areas of the lake are recommended.

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