Papers by Ogutu-Ohwayo Richard
Aquatic Ecosystem Health & Management, 2016
Climate variability and change that have been intensifying since the 1970s are accompanied by cha... more Climate variability and change that have been intensifying since the 1970s are accompanied by changes in hydrology and water balance of inland aquatic systems. These changes, however, have not been well documented with regard to small and shallow aquatic systems that are more vulnerable. Changes in temperature, rainfall and wind speed around Lakes Wamala and Kawi (Uganda) were examined to provide insight on how the increasing variability and change in climate affect water balance and lake water levels. Around Lake Wamala, average air temperature has increased by 0.018°C y−1 since 1980. Rainfall increased by 9.01 mm y−1 since 1970 and accounted for 79.5% of the water gain during 2011 and 2013 period. However, the gains were exceeded by losses as a result of evaporation that accounted for >85% of the water loss. Despite the increase in rainfall, the mean lake depth of Lake Wamala decreased by 0.015 m y−1, apparently due to high evaporation rates. Around Lake Kawi, average air tempe...
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Environmental Biology of Fishes, 1997
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Lakes & Reservoirs: Science, Policy and Management for Sustainable Use, 2006
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Journal of Fish Biology, 1990
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Conservation Biology, 1996
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Conservation Biology, 2008
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Canadian Journal of Fisheries and Aquatic Sciences, 1991
Fish introductions in Africa have been made at various spatial scales from small fish ponds to th... more Fish introductions in Africa have been made at various spatial scales from small fish ponds to the largest lakes, primarily to sustain or increase production, though some were to develop sport fisheries and to control unwanted organisms. Some introductions have fulfilled their objective in the short term, but several "successful" introductions have created uncertainties about their long-term sustainability. Lates niloticus, Oreochromis niloticus, O. leucostictus, Tilapia melanopleura and T. zilli were introduced into Lakes Victoria and Kyoga in 1950's and early 1960's; by the 1980's L. niloticus and O. niloticus dominated the fisheries, having virtually eliminated a number of endemic species. In Lake Victoria, the loss of genetic diversity has been accompanied by a loss of trophic diversity; the transformation of the fish community coincided with profound eutrophication (algal blooms, fish kills, hypolimnetic anoxia) which might be related to alterations of the...
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African Journal of Ecology, 2004
ABSTRACT Prior to the 1980s, lakes Kyoga and Victoria previously supported an exceptionally diver... more ABSTRACT Prior to the 1980s, lakes Kyoga and Victoria previously supported an exceptionally diverse haplochromine fish fauna comprising at least 11 trophic groups. The species and trophic diversity in these lakes decreased when the introduced Nile perch depleted haplochromine stocks. From December 1996 to October 1998, we studied species and trophic diversity of haplochromine fishes in six satellite lakes without Nile perch in the Kyoga basin and compared them with the Kyoga main lake against historical data from Lake Victoria where Nile perch were introduced. Forty-one species were found in the study area, of which, the Kyoga satellite lakes contributed 37 species in comparison to only 14 from the Kyoga main lake. Analysis of trophic diversity based on 24 species that contained food material revealed seven haplochromine trophic groups (insectivores, peadophages, piscivores, algal eaters, higher plant eaters, molluscivores and detritivores) in the Kyoga satellite lakes in comparison to two trophic groups (insectivores and molluscivores) in the Kyoga main lake. Many of the species and trophic groups of haplochromines depleted by the introduced Nile perch in lakes Kyoga and Victoria still survive in the Kyoga satellite lakes. This is attributed to the absence of Nile perch in those lakes. Nile perch has been prevented from spreading into the satellite lakes by swamp vegetation that separate them from the main lakes. If these swamps prevent Nile perch from spreading into the lakes, it is possible to conserve fish species, especially haplochromines, which are threatened by introduction of Nile perch in the main lakes. Avant les années 1980, les lacs Kyoga et Victoria renfermaient une variété exceptionnelle de poissons du genre Haplochromis, qui comptait au moins 11 groupes trophiques. La variété des espèces et des groupes trophiques de ces lacs a diminué après que l'introduction de la perche du Nil a dévasté les stocks d'Haplochromis. De décembre 1996 à octobre 1998, nous avons étudié la diversité des espèces et des groupes trophiques d'Haplochromis dans six lacs satellites du bassin du Kyoga qui ne contenaient pas de perches du Nil et nous l'avons comparée à celle qui existe dans le lac Kyoga principal, en regard des données antérieures sur le lac Victoria, où l'on a aussi introduit la perche du Nil. On a découvert quarante et une espèces dans la zone étudiée, dont 37 sont présentes dans les lacs satellites pour seulement quatorze dans le lac Kyoga lui-même. L'analyse de la diversité trophique basée sur 24 espèces qui contenaient du matériel alimentaire a révélé sept groupes trophiques chez les Haplochromis (insectivores, pédophages, piscivores, mangeurs d'algues, de plantes supérieures, de mollusques, et détritivores) dans les lacs satellites du Kyoga, pour deux groupes trophiques seulement (insectivores et mangeurs de mollusques) dans le lac Kyoga lui-même. Nombreux sont les groupes trophiques et les espèces d'Haplochromis qui ont été décimés par l'introduction de la perche du Nil dans les lacs Kyoga et Victoria et qui survivent dans les lacs satellites du Kyoga. On attribue cet état de fait à l'absence de perches du Nil dans ces lacs. La dispersion de la perche du Nil vers les lacs satellites a été empêchée par la végétation des marécages qui les séparent des lacs principaux. Si ces marécages réussissent à empêcher la perche du Nil de se répandre dans les lacs satellites, il est possible de préserver des espèces de poissons, et spécialement des Haplochromis, qui sont menacées par l'introduction de la perche du Nil dans les lacs principaux.
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African Journal of Aquatic Science, 2004
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African Journal of Ecology, 2006
ABSTRACT Abstract The tilapiine fish Oreochromis esculentus, is endemic to only lakes Victoria an... more ABSTRACT Abstract The tilapiine fish Oreochromis esculentus, is endemic to only lakes Victoria and Kyoga and a few satellite lakes in the two lake basins. It was the most important commercial fish species during the first half of the 20th century in the two lake basins but because of over-exploitation and competition with introduced tilapiines, its stocks declined and, by 1980s, O. esculentus was virtually absent from the two main lakes. Lakes Mburo, Kachera, Kayanja and Kayugi in the Lake Victoria basin, and Nabisojjo, Kawi and Lemwa, in the Lake Kyoga basin, where remnants of the species survived were investigated using experimental fleets of gillnets from 1997 to end of 2002 with the objective of determining the species length frequency distribution, condition factor, feeding and breeding to guide its management, conservation and enhancement. Fish caught in Lake Kayugi, where diatoms dominated in the stomach contents attained the largest size, were most fecund and had a high value of condition factor K. These findings suggest that diatoms were vital in the survival of O. esculentus. However, with the recent shift of algal communities from diatoms to blue-green algae in most aquatic systems, assimilation of blue-green algae by O. esculentus should be investigated.
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African Journal of Ecology, 2009
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The Behavior, Ecology and Evolution of Cichlid Fishes, 2021
Lakes Victoria, Kyoga, and Nabugabo ("the Lake Victoria region") are remarkable... more Lakes Victoria, Kyoga, and Nabugabo ("the Lake Victoria region") are remarkable for hosting one of the largest assemblages of cichlid fishes among the African inland lakes. Here, we review the role and severity of anthropogenic and environmental stressors on the cichlid communities in the Lake Victoria region to understand the mechanisms leading to the persistence and resurgence of some of the cichlid fishes. Our review suggests that (1) the native Oreochromis species populations primarily collapsed due to overfishing and that the introduced species and habitat change suppressed their ability to recover; (2) without primary triggers associated with change in the environment and habitat conditions, particularly
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African Journal of Aquatic Science, 2013
ABSTRACT The Kyoga lake system, which is c. 4 m deep, originally had a diverse fish fauna, extens... more ABSTRACT The Kyoga lake system, which is c. 4 m deep, originally had a diverse fish fauna, extensive macrophytes and wetlands. Most (82%) of its water comes from Lake Victoria, is controlled through three dams and has a short residence time of c. 3 months. Physical and chemical factors, plankton productivity and composition vary across the lake from east to west. The macrophyte cover decreased after the heavy El Niño rains of 1961, and the area of wetlands decreased by 48.5% between 1994 and 2008 mainly because of their conversion to agriculture. The main lake was infested with water hyacinth in the 1990s but subsequently this was brought under control. The native fishes were overexploited and non-native fishes, including a top piscivore, Nile perch Lates niloticus L., were introduced and boosted fish production, but they also were overexploited. Nile perch also preyed upon and decimated native species, which survived only in satellite lakes. Populations of some of these species recently have started to recover in the main lake. Efforts should be made to control habitat loss and water-level fluctuations, wetland loss, overexploitation of the fishes, conserve the surviving fish species and address the emerging challenge of climate change.
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Lakes & Reservoirs: Research & Management, 2015
Changes in the catches of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), in Lake Wamala (U... more Changes in the catches of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), in Lake Wamala (Uganda) have been observed since its introduction. The factors contributing to these changes, however, are not well understood. This study examined changes in species composition, size structure, size at first maturity, length–weight relationship and condition factor of Nile tilapia in Lake Wamala, in relation to changes in temperature, rainfall and lake depth, to provide a better understanding of the possible role of changing climatic conditions. There was an increase in the minimum, maximum and average temperatures since 1980, but only the minimum (0.021 °C year−1) and average temperatures (0.018 °C year−1) exhibited a significant trend (P < 0.05). Rainfall increased by 8.25 mm year−1 since 1950 and accounted for 79.5% of the water input into the lake during the period 2011–2013, while evaporation accounted for 86.2% of the water loss from the lake. The lake depth was above 4 m during the years when the rainfall exceeded the average of 1180 mm, except after 2000. The contribution of Nile tilapia to total fish catch and catch per unit effort (CPUE) increased with rainfall and lake depth up to the year 2000, after which they decreased, despite an increased rainfall level. The lake depth was positively correlated with the average total length and length at 50% maturity (r = 0.991 and 0.726, respectively), while the slopes of the length–weight relationships differed significantly between high and low lake depths [t(6) = 3.225, P < 0.05]. Nile tilapia shifted from an algal-dominated diet during the wet season to include more insects during the dry season. The results of this study indicate Nile tilapia in Lake Wamala displays a typical r-selected reproductive strategy, by growing to a small size, maturing faster and feeding on different food types, in order to survive high mortality rates under unfavourable conditions attributable to higher temperatures, low rainfall and low lake water levels.
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Molecular Ecology, 1998
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Natugonza et al. 2021, 2021
Lakes Victoria, Kyoga, and Nabugabo ("the Lake Victoria region") are remarkable for hosting one o... more Lakes Victoria, Kyoga, and Nabugabo ("the Lake Victoria region") are remarkable for hosting one of the largest assemblages of cichlid fishes among the African inland lakes. Here, we review the role and severity of anthropogenic and environmental stressors on the cichlid communities in the Lake Victoria region to understand the mechanisms leading to the persistence and resurgence of some of the cichlid fishes. Our review suggests that (1) the native Oreochromis species populations primarily collapsed due to overfishing and that the introduced species and habitat change suppressed their ability to recover; (2) without primary triggers associated with change in the environment and habitat conditions, particularly
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African Journal of Aquatic Science, 2013
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Papers by Ogutu-Ohwayo Richard