Efficiency, energy and stoichiometry in pelagic food webs; reciprocal roles of food quality and food quantity

In most lakes, zooplankton production is constrained by food quantity, but frequently high C:P poses an additional constraint on zooplankton production by reducing the carbon transfer efficiency from phytoplankton to zooplankton. This review addresses how the flux of matter and energy in pelagic food webs is regulated by food quantity in terms of C and its stoichiometric quality in terms of C:P. Increased levels of light, CO2 and phosphorus could each increase seston mass and, hence, food quantity for zooplankton, but while light and CO2 each cause increased C:P (i.e. reduced food quality for herbivores), increased P may increase seston mass and its stoichiometric quality by reducing C:P. Development of food quality and food quantity in response to C- or P-enrichments will differ between 'batch-type' lakes (dominated by one major, seasonal input of water and nutrients) and 'continuous-culture' types of lakes with a more steady flow-rate of water and nutrients. The reciprocal role of food quantity and stoichiometric quality will depend strongly on facilitation via grazing and recycling by the grazers, and this effect will be most important in systems with low renewal rates. At high food abundance but low quality, there will be a 'quality starvation' in zooplankton. From a management point of view, stoichiometric theory offers a general tool-kit for understanding the integrated role of C and P in food webs and how food quantity and stoichiometric quality (i.e. C:P) regulate energy flow and trophic efficiency from base to top in food webs.From a management point of view, stoichiometric theory offers a general tool-kit for understanding the integrated role of C and P in food webs and how food quantity and stoichiometric quality (i.e. C:P) regulate energy flow and trophic efficiency from base to top in food webs.

The production of freshwater fish for food

It has been estimated that in England and Wales fresh water covers some 340 square miles of which about one quarter is inhabited mainly by salmon and trout; in Scotland the lakes cover an area of 340 square miles. The principal object of this publication is to make available in handy form some of the methods, especially those involving the use of manures, by which crops of fish from water can be increased. The cultivation of water which this implies may be compared directly to the cultivation of farm land: the conditions for growth are made as favourable as possible, the seed is sown in the form of young fish, and after one or perhaps two growing seasons the crop is harvested. There are however many waters about the country where marketable fish are already available and can be removed without prejudice to, and indeed to the advantage of, sporting fisheries. In such cases it is necessary only to remove the fish and to rely on the natural processes of reproduction of those which are left to repopulate the water. Farming waters in the true sense is the concern of the greater part of this publication; the removal of crops of otherwise unwanted fish is considered in the last two sections on perch trapping and eel fisheries.

Simula����o biofisicoqu��mica em reservat��rio tropical polim��tico

O reservat��rio do Lobo, localizado no estado de S��o Paulo, �� um sistema din��mico no qual se desenvolve um ciclo diurno de estratifica����o e mistura, de modo similar ao que tem sido observado em outros lagos tropicais. Utilizou-se simula����o 3D computacional com os softwares ELCOM (Estuary and Lake Computer Model) acoplado ao CAEDYM (Computacional Aquatic Ecosystem Dynamics Model), ambos desenvolvidos pelo CWR (Center for Water Research) da Universidade da Austr��lia. Foram realizadas cinco simula����es: Piloto Primavera baseada em dados reais da esta����o no ano primavera no reservat��rio para o ano de 2007; Primavera-P em que as concentra����es de f��sforo total, fosfato inorg��nico e fosfato total dissolvido foram aumentadas em 100% no reservat��rio (coluna de ��gua e sedimento) e nos rios tribut��rios; Primavera-V na qual a intensidade dos ventos foi aumentada em 50%; Primavera-T onde a temperatura da ��gua (reservat��rio e tribut��rios) e do ar foram aumentadas em 10C e, Primavera-X, onde a temperatura da ��gua (reservat��rio e tribut��rios) e do ar sofreu aumento em 10C, as concentra����es de f��sforo total, fosfato inorg��nico e fosfato total dissolvido foram aumentadas em 100% e a velocidade do vento aumentada em 50%. A concentra����o de clorofila a foi representada pelos grupos cianobact��rias e clorof��ceas. O espa��o de tempo das simula����es representou 90 dias. As clorof��ceas apresentaram maior desenvolvimento populacional do que as cianobact��rias em todas as simula����es. No reservat��rio, a mistura vertical �� ocasionada diariamente pelo vento ou por processos convectivos causados pela perda de calor no corpo de ��gua. A oxigena����o do reservat��rio �� maior com a ocorr��ncia de ventos e de grupos fotossint��ticos. As concentra����es totais de f��sforo e nitrog��nio apresentaram aumento em todas as simula����es.

Hist��ria ambiental e paisagens simb��licas no munic��pio de S��o Pedro da Aldeia (RJ): a Lagoa de Araruama e a Serra de Sapiatiba

Este trabalho visa contribuir com os estudos de Hist��ria Ambiental e de Geografia ao abordar a intera����o entre os aspectos culturais e a natureza da Lagoa de Araruama e da Serra de Sapiatiba, localizado no Estado do Rio de Janeiro. A pesquisa prop��e uma an��lise das paisagens simb��licas do munic��pio de S��o Pedro da Aldeia (RJ) por interm��dio do 3 n��vel da Hist��ria Ambiental. Al��m de caracterizar estas ��reas como paisagens simb��licas inseridas na Regi��o dos Lagos numa ��rea de Prote����o Ambiental (APA de Sapiatiba), destaca-se a import��ncia do capital imaterial e da hist��ria ambiental na conserva����o da diversidade de um pequeno fragmento de Mata Atl��ntica e tamb��m da natureza das ��guas em um importante trecho da maior lagoa hipersalina do mundo. Portanto, nosso objetivo neste estudo �� desvendar a Hist��ria Ambiental da Lagoa de Araruama e da Serra de Sapiatiba no munic��pio de S��o Pedro da Aldeia (RJ), a partir da an��lise da transforma����o da paisagem.

An analysis of salmon rod catch data from castle fisheries, River Derwent, 1923-1989.

The aim of this study was to investigate the historical catch record from the Castle Fishery on the River Derwent over the period 1923 - 1989, to determine if changes had taken place in the composition of the catch and to examine the influence of flow on the performance of the fishery. The River Derwent is situated in West Cumbria, North West England. It flows from its source on Scafell Pike (NGR NY 229 089) westwards discharging into the Irish sea at Workington, a distance of 52 km. Over its length it receives water from an additional 214 km of stream, 5 large lakes and approximately 30 small tarns. The catchment drains a total area of 663 km2. The study concludes that through the time period there was considerable variation in catch between years. The trend was for the catch to increase steadily over the period 1923 - 1958, declining rapidly in 1959, after which catches increased steadily reaching a peak in the mid-sixties, before declining towards the end of the decade. During the seventies and eighties catches remained relatively stable at between 300 - 600 salmon per year until 1988 when over 2000 salmon were reported caught, the greatest number in any year over the study period.

Aspects of the biology and population dynamics of freshwater mussels in Lake Kariba and Lake McIlwaine

The essential aim of this study was to provide a broad foundation of biological knowledge upon which a programme of mussel utilization and management could be built. Results of the study are presented in three main sections. Part 1 describes the stock of Lake Kariba and Lake McIlwaine; part 2 describes various aspects of the breeding biology of the three species; and part 3 presents the results of morphological, biochemical and age analyses - aspects which are used for initial standing crop and production calculations. The final discussion concludes the thesis with a general examination in ecological terms of the factors which have influenced the development and nature of the mussel faunas of the two lakes under consideration.

A bacia hidrogr��fica Lagos-S��o Jo��o p��s d��cada de 1960: um estudo das transforma����es espaciais da regi��o e suas influ��ncias sobre a qualidade ambiental

A Bacia Hidrogr��fica Lagos S��o Jo��o, localizada no sudoeste do Estado do Rio de Janeiro, abrange 13 munic��pios que abrigam cerca de 520 mil habitantes. Na temporada de f��rias esse n��mero sobe para mais de 1 milh��o de pessoas. A pastagem constitui o principal tipo de uso do solo, em seguida vem as ��reas urbanas e as salinas. A partir da d��cada de 1960 essa regi��o passou a receber maior contingente populacional, tanto de veranistas quanto de moradores fixos, beneficiados pela implanta����o de novas vias de acesso, como a Ponte Rio-Niteroi e pela constru����o da represa de Juturna��ba, que ampliou o abastecimento de ��gua dos munic��pios. Surge neste contexto a especula����o imobili��ria, que acelera a ocupa����o das terras pr��ximas a Lagoa de Araruama. Rapidamente essas terras foram loteadas e o setor da constru����o civil foi ganhando for��a. Entretanto, a regi��o n��o contou com adequado planejamento, e os investimentos em saneamento b��sico e outras infraestruturas urbanas n��o acompanharam o ritmo da constru����o civil, que cada vez mais investia em casas, pr��dios e condom��nios, que ampliaram consideravelmente a ��rea urbana e a ocupa����o da zona costeira. Sendo assim, ficou vis��vel o aumento da malha urbana e a ocupa����o de ��reas impr��prias, como as margens dos corpos h��dricos, os manguezais, dunas e restingas, al��m da redu����o da cobertura vegetal. Dessa forma, foi substancial a perda de qualidade ambiental na regi��o, sobretudo, com rela����o a ��gua da lagoa e dos rios, que passaram a receber maior volume de efluentes sem tratamento. O potencial tur��stico da regi��o tem sido explorado e provocado altos investimentos dos agentes de especula����o imobili��ria, entretanto al��m de promover a ocupa����o em ��reas irregulares, leva a privatiza����o de espa��os p��blicos e incentiva o fen��meno da segunda resid��ncia. A chegada de novos turistas iniciou o processo de desenvolvimento do turismo e, consequentemente, a redu����o da produ����o salineira. Com isso, o espa��o local ganhou novos significados, inseridos pela l��gica da urbaniza����o tur��stica. Foi essa nova l��gica transformadora que, gradativamente, valorizou a paisagem local, ampliando e encarecendo o seu consumo. Al��m de ampliar as transforma����es espaciais, tendo em vista a expans��o da malha urbana verificada nas imagens de sat��lites, atuais, que foram comparadas com fotografias a��reas de d��cadas anteriores. Todas as transforma����es ocorridas na regi��o apresentam alguma rela����o com o desencadeamento de novos problemas ambientais identificados nos seus ecossistemas, sobretudo a Lagoa de Araruama, ou a amplia����o de problemas anteriormente existentes.

The structure and margins of the Lake Chilwa fisheries in Malawi: a value chain analysis

Small freshwater pelagic fisheries in closed lakes are very important to millions of people in sub-Saharan Africa providing livelihoods and nutritional security. However, returns from these fisheries have been shown to ���uctuate in response to climatic variability. In order to understand the impact of these fluctuations on the livelihoods of people dependant on these fisheries, there is a need for information on how the fish value chain is organized and how it functions in response to variation in supplies. The results will feed into strategies that build resilience in fishing households against the uncertainties arising from unstable ecosystems. The Lake Chilwa fishery value chain is composed of fishers, processors, traders, fish transporters, boat owners, owners of fish processing shades, fisheries associations, gear owners, gear makers, firewood sellers, and traders of fishing gear and equipment. The value chain employs many people and local authorities can consider using this information in the design of rural development strategies for employment generation in small-scale fishing communities. The findings from this study have a number of implications for the improvement of the livelihood of fishers and enhancing their capacity to mitigate against the effects of climate change.

Diversidade e aspectos bioecol��gicos de simul��deos (Diptera: Simuliidae) que ocorrem nos munic��pios adjacentes a constru����o da usina Hidrel��trica de Peixe-Angical, TO, Brasil

O objetivo desta Tese �� realizar o levantamento taxon��mico e avaliar a din��mica populacional de Simuliidae em localidades sob influ��ncia do Aproveitamento Hidrel��trico de Peixe Angical, TO. Os simul��deos possuem abrangente distribui����o geogr��fica, e os est��gios imaturos utilizam ambientes l��ticos como s��tios de cria����o. Algumas esp��cies podem atuar como vetores de v��rus, protozo��rios e helmintos, o que confere ao grupo import��ncia m��dica e veterin��ria. O h��bito hematof��gico das f��meas de simul��deos pode acarretar s��rios preju��zos ao turismo; ocasiona baixa no rendimento escolar; e na agropecu��ria dificulta a execu����o do trabalho o que reduz a produtividade. Durante a constru����o de grandes empreendimentos ocorre em pouco tempo �� introdu����o de contingente populacional com dr��stica transforma����o do meio. A interven����o do homem sobre os ecossistemas e o crescimento desordenado pode provocar desequil��brio ecol��gico que propicia a prolifera����o de esp��cimes vetores com consequentes problemas m��dico sanit��rios. A maior parte dos trabalhos realizados com insetos vetores em ��reas sob influ��ncia da constru����o de hidrel��tricas se refere aos culic��deos. O estudo dos aspectos taxon��micos permitir�� o levantamento da biodiversidade e o diferencial deste projeto est�� no estabelecimento da sazonalidade e din��mica das popula����es de imaturos e adultos de simul��deos. As amostras foram obtidas em ��reas de influ��ncia direta e indireta da UHE Peixe no rio Tocantins, em 12 pontos diferentes de coleta, nos munic��pios deJa�� do Tocantins, Peixe, Palmeir��polis, Paran�� e S��o Salvador do Tocantins. Foram realizadas bimestralmente de 2004 a 2007, um total de 24 campanhas para coleta em criadouros pr��-selecionados, que acompanharam todas as fases de constru����o in��cio das obras, forma����o do lago, funcionamento da Usina. OS dados abi��ticos foram aferidos, e os imaturos removidos do substrato manualmente por 10 minutos e posteriormente preparados para eclos��o dos adultos. Parte do material foi identificado no Laborat��rio de Simul��deos e Oncocercose do Instituto Oswaldo Cruz, onde foram verificados novos registros espec��ficos para a ocorr��ncia de Simuliidae em Tocantins, al��m do assinalamento de esp��cies antropof��licas e/ou vetores de Onchocerca volvulus. Nas ��reas usadas para a forma����o do lago houve desaparecimento de criadouros. O desmatamento ocorrido aliado ao vigor dos simul��deos que conseguem realizar voos de longas dist��ncias na procura de alimento ou locais adequados a oviposi����o devem ter contribu��do para a dispers��o de esp��cimes. H�� relatos sobre a da ocorr��ncia de oncocercose na ��rea estudada, um foco foi demarcado na divisa de Goi��s com Tocantins, munic��pios Paran�� e Mina��u investigado a partir de um caso aut��ctone de oncocercose. Este estudo �� relevante uma vez que o Brasil possui potencial hidroenerg��tico e prev�� a constru����o de in��meras hidrel��tricas nos pr��ximos anos. �� importante estudas as ��reas impactadas, conhecer a sua biodiversidade e os aspectos bioecol��gicos de Simuliidae no pa��s.

CGIAR aquatic research priorities revisited: a case for a higher priority for reservoir-lake system research

The case presented in this article clearly indicates that reservoir and lake resource systems, reservoirs in the Asian context lakes plus reservoirs in the African context, have been given a lower priority than deserved.

Impact of development and dissemination of Integrated Aquaculture-Agriculture (IAA) Technologies in Malawi

Malawi is a small but densely populated country in Southern Africa. Fish is an important part of the nutrition of Malawians, providing essential protein and micronutrients. However, per capita fish consumption has halved over the ten-year period between 1988 to 1998 due to over-fishing in the lakes and doubling of the population since the 1970s, accompanied by an increase in the price of fish. This has worsened access to food insecurity, especially in rural areas, in a country where an estimated 66 per cent of the population consume less than the minimum daily calorie requirement. This paper presents an ex-post impact assessment of the development and dissemination of smallscale integrated aquaculture-agriculture technologies by The WorldFish Center and its national and international partners over more than 15 years in Malawi. The impact study measures the effects of these outputs on the degree of integrated aquaculture-agriculture (IAA) technology adoption and diffusion, the effects on farm income and health of household members, and the welfare effects of increased fish supply on the Malawian economy.

Investing in Africa: the WorldFish Center's African strategy in summary

Across much of Africa, freshwater and coastal fisheries provide an important source of food and livelihood for many millions of people. In addition, the aquaculture potential of the continent has only recently begun to be developed. To help sustain these capture fisheries, support the emergence of aquaculture and foster the contribution of both to sustainable livelihoods and improved food security, the WorldFish Center is increasing its investment in Africa. The framework for this investment is provided by a new Strategy for Africa and West Asia 2002-2006 that identifies priorities for the Center���s work in rivers and floodplains, lakes and reservoirs, coastal fisheries, aquaculture, policy research and capacity building. The present article summarizes the issues being addressed by the Center and describes initial research priorities.

An annotated checklist of freshwater fishes of Armenia

A list of freshwater fishes inhabiting lakes, reservoirs and rivers of Armenia is presented which include 39 species and subspecies belonging to 5 orders, 9 families and 29 genera. A brief description of the ecology, distribution and present status (introductions, threats, commercial value) of these fishes is given.

Breeding and propagation of tilapia (Oreochromis niloticus) in a floating hatchery, Gabon

Based on the encouraging results obtained by earlier workers, the concept for a floating hatchery was developed for producing tilapia for both farming and enhanced fisheries in the freshwater lakes and coastal lagoons of Gabon. The research and development work to test this concept was undertaken with Nile tilapia (Oreochromis niloticus). Two places in Gabon were selected, representing climatic and environmental condition similar to other parts of the country. The study aims to improve fish production in the freshwater lakes of the Lambarene area, and in the numerous coastal lagoons of Gabon, to compensate for the current overexploitation of natural stocks, or the alternative of introducing other species, and to reduce the drift of fishing population away from lakes.

A preliminary study on the feasibility of using fenced brushparks for fish production in Lake Chilwa, Malawi

A study to investigate the feasibility of using fenced brushparks for fish ranching in Lake Chilwa was conducted for five months at the Kachulu Harbor. In a water depth of 1.4 m enclosures constructed from bamboo sticks embedded in the sediment and surrounded by a 13 mm seine net, were filled with three different subrates (Typha, bamboo, and Sesbania branches) and a no substrate enclosure served as a control. Netting materials contributed 57 per cent towards the total cost (US$ 0.24-0.30/m2) of brushpark contruction. Fish productivity was highest in the Typha, bamboo and control treatments and lowest in the Sesbania treatments. The decomposition of substrates did not affect water quality. The results indicate that enclosed brushparks may be a feasible technology for enhancing fish yields and providing alternative income sources to fisherfolk in small lakes and water bodies.