Aspects of the ecology of the crustacean zooplankton in the Sanyati Basin, Lake Kariba

Investigations on the zooplankton in Lake Kariba were carried out as part of a broader programme investigating components of the sardine, Limnothrissa miodon, food chain and factors affecting their productivity. This report deals mainly with the crustacean zooplankton, Bosmina longirostris and Mesocyclops leuckarti, which are the most important species in the sardine's diet. Factors which influence the number and distribution of the zooplankton are discussed. The relationship between the zooplankton and Limnothrissa are also briefly discussed.

Preliminary phytoplankton counts in the Sanyati Basin, Lake Kariba

Phytoplankton counts were made on a monthly basis on water samples, taken from one station in the Sanyati Basin. The results show seasonal fluctuations which are probably nutrient dependant. High phytoplankton numbers occur at times of high nutrient levels as was found with the crustacean zooplankton populations (Marshall 1980). Numbers also decreased with depth down to the thermocline. Below the thermocline there was little or no change in numbers.

Fish and fisheries in the Sesan River Basin: catchment baseline, fisheries section

The present report was prepared for the Water and Food Challenge Program project “Optimizing the management of a cascade of reservoirs at the catchment level” (MK3). It constitutes the baseline assessment of fish and fisheries in the Sesan River Basin. The objective of the MK3 project is to contribute knowledge and recommendations so that cascades of reservoirs corresponding to hydropower dams in the Mekong Basin are managed in ways that are more fair and equitable for all water users. This project seeks to understand at the catchment scale the cumulative upstream and downstream consequences of management decisions taken for multiple reservoirs. Revised rules for water storage infrastructure management will in particular take into account fisheries and agricultural potential as well as hydropower gen

Economic incentives for water resource management in the Pak Phanang river basin of southern Thailand

The study examines the existing water allocation methods and other policies that provide constraints or incentives for the most efficient use of water resources. Given the production condition of the local people, and the technical and physical attributes of water resources, the principal hypothesis of this study is that the benefits obtained from fresh water resources in the study area can be improved through better resource management.

Two new species of Zospeum Bourguignat, 1856 from the Basque-Cantabrian Mountains, Northern Spain (Eupulmonata, Ellobioidea, Carychiidae)

Two new species of the genus Zospeum Bourguignat, 1856 are described from caves in the Sierra de Aitzgorri (Gipuzkoa) and the Sierra Salvada (Burgos) in Northern Spain. The taxa Z. vasconicum sp. n. and Z. zaldivarae sp. n. have recently, without a formal name, been included in a molecular study of worldwide members of the Carychiidae. In the present paper, the shell morphology and variation of these species is described and illustrated.

Palaeoenvironmental analysis based on alluvial ostracod assemblages of the Cenicero section (lower Miocene, NW Ebro Basin)

In this work we perform for the first time a palaeoenvironmental and biostratigraphic analysis of the lower Miocene alluvial deposits of the Cenicero section (NW sector of the Ebro Basin; N Iberian Peninsula), based on the ostracod and micromammal assemblages. One of the main characteristics of this section is the unusual abundance on non-reworked ostracods present in the studied samples compared to other European sequences of similar age and sedimentary environment. This fact has allowed us to develop precise palaeoenvironmental reconstructions. The variations of the identified ostracod assemblages, defined by species such as Cyclocypris laevis, Ilyocypris bradyi, Ilyocypris gibba, Limnocythere sp. or Pseudocandona parallela, record the development of small, ephemeral and shallow ponds in a distal alluvial and/or floodplain environment. Towards the upper part of the section the ponds appear to be less ephemeral, being the aquatic systems more stable for ostracods development. Variations in the water temperature and salinity have been observed along the section, which are related to changes in the local pluviometric regime. On the other hand, the presence of micromammals in one of the studied samples has allowed the precise dating of this section. Thus, the presence of Armantomys daamsi dates the Cenicero section as Agenian (lower Miocene), local zone Y2 (MN2).

Aquaculture in the mountains of the northern Lao PDR and northern Vietnam

This article features the current status of aquaculture in the mountains of the northern Lao PDR and northern Vietnam.

Observations on gillnet catches of Kariba tilapia, Oreochromis mortimeri from Bumi Basin of Lake Kariba, Zimbabwe

Gillnet catches of Oreochromis mortimeri (Trewavas) were studied in the Bumi Basin of Lake Kariba in 1988 and 1989. Total length (TL) was positively correlated with standard length (SL). The linear relationship between TL and SL was TL=1.91 + 1.22 SL (r super(2)=0.982). The relationship between SL and weight in g (W) was of the form W = 0.12 SL super(2.67). Maximum standard length (L sub(max)) was 33 cm and asymptotic length (L sub( infinity )) was 34.7 cm. Monthly ratios of male to female varied between 0.6:1 and 13:1. The mean ratio was 57.4% male: 42.6%female. Monthly condition factors varied between 3.19 and 5.11 in males, and between 3.18 and 5.14 in females. Catches were higher in 1989 compared to 1988 and possible reasons for these differences are discussed.

Management of wetland resources in the lower Mekong Basin: issues and future directions

The Lower Mekong Basin has extensive wetlands and these are being threatened by numerous problems. Most of these problems are interdependent and interact with one another. The lack of an appropriate definition of wetlands applicable to the region, pervasive inefficiencies and chronic lack of funds among riparian governments, and the poor appreciation of the true economic importance of wetlands and its resources are among the most prominent. The current definition, based on the Convention on Wetlands (Ramsar, Iran, 1971), is too broad when compared to the understanding of wetlands as being swamps, marshes and the like, and was developed specifically for wetlands with international importance as waterfowl habitats. Furthermore, wetlands are composed of different types of resources, which require different modes of management. Often, institutional competition, overlapping mandates and sometimes jealousies occur between government departments when they try to assert their authority on a particular wetland resource and use, and put forward their development plans without considering how these may conflict with other wetlands uses. Finally, effective wetland management requires reliable statistics or information on rate of harvest of natural resources such as fish and others, fishing/harvesting methods over time in order to determine the level of exploitation, and the status of the natural resources. This information is needed to identify opportunities for expansion, to establish historical trends, and to determine when management interventions are necessary to protect the resources from being overused by other developments. In order to address these issues, ICLARM - The World Fish Center has launched a project, the aim of objectives of which are described in this paper.

Termocronologia (U-Th)He e reativação da margem continental do sudeste do Brasil: seção Serra da Mantiqueira - Gráben da Guanabara

A evolução da margem continental do sudeste do Brasil tem sido discutida por diversos autores desde meados do século passado até os dias atuais, especialmente no contexto da origem e evolução dos escarpamentos e das bacias tafrogênicas. Buscou-se contribuir com novos dados sobre a evolução da área a partir da aplicação da termocronologia de baixa temperatura (U-Th)/He em apatita, que oferece uma sensibilidade significativa para registrar movimentações tectônicas na crosta superior. Foi possível obter idades em 107 cristais de apatita de 18 amostras do embasamento coletadas no perfil com orientação NW-SE, numa seção entre a Serra da Mantiqueira e o Gráben da Guanabara. As idades corrigidas variam entre 250,1 8,7 Ma e 43,5 1,9 Ma (2 σ) e as não corrigidas entre 174,13 3,03 Ma e 27,07 0,60 Ma (1 σ). O Neocretáceo, o Eocretáceo e o Paleoceno são os principais registros no conjunto de dados, em ordem de importância. No Neocretáceo, o intervalo entre 83,6 e 72,1 Ma (Campaniano) representa o maior destaque nos registros termocronológicos, embora os outros registros (Maastrichtiano e Santoniano) também estejam presentes e sejam importantes. As idades do Neocretáceo destacam a importância dos eventos tectonomagmáticos e soerguimento regional na história térmica dessa área, inclusive com idades (~86 Ma) atribuídas ao contexto de soerguimento da Serra do Mar. As idades do Eocretáceo indicam o registro de eventos térmicos mais antigos, vinculados à evolução pré-rifte. Já os dados do Paleoceno estariam associados ao evento de reativação responsável pela implantação do sistema de riftes continentais (~65 Ma) e as idades do Eoceno, restritas à borda de falha da bacia de Resende (49,7 Ma e 43,5 Ma), à reativação do sistema de riftes nessa área. A dispersão de idades foi interpretada como efeito dos danos de radiação já que muitos grãos apresentam correlação entre idade e concentração de urânio (eU). Os padrões de tempo-temperatura (t-T), definidos a partir dos modelos HeFTy calibrados para o modelo de difusão que considera os efeitos de danos de radiação nos cristais, registraram eventos de resfriamento rápido, os quais mostram correlação direta com episódios de reativação e soerguimento na margem continental e com registros nas bacias continentais e marginais. O padrão de aumento das idades com a elevação, assim como da costa em direção ao interior é observado, mas mostra-se alterado pela ocorrência de idades mais jovens associadas à complexa evolução dessa margem continental com desnivelamentos de blocos vinculados à tectônica pós-rift, numa situação que ressalta a influência dos episódios de reativação. As estimativas de denudação total variam entre 1,2 e 2,8 km. As taxas de erosão variam entre 15,2 e 35,3 m/Ma. A evolução da área indica não apenas a influência de um evento específico mas, possivelmente, uma combinação de episódios que se alternaram e/ou atuaram em conjunto em determinados períodos. Os eventos de reativação mais antigos, combinados com os mais recentes, exibem os seus remanescentes na paisagem (serras da Mantiqueira e do Mar e os grábens e bacias sedimentares) e assumem papel fundamental na evolução da área. Os registros de tais episódios podem ser observados nas histórias térmicas das rochas e nos depósitos correlativos nas bacias sedimentares marginais e intracontinentais.