The effects of a dam closure (Porto Primavera Dam) on reproduction of the main species that use the floodplain located below a nursery area were determined. Specifically, we examined, before and after the closure of the dam, the spatial distribution of larvae and the differences in density according to life strategy (migratory and non-migratory species). Fifteen points distributed along the channels of the Paraná, Ivinheima and Paranapanema rivers were sampled, between 1997 and 2001, (October 1997 to December 1998 and between January 1999 to March 2001-post closure), during the spawning period of most fish species found in the region (October to March). Samplings were always conducted at night, using a conical-cylindrical plankton net (0.5 mm mesh) with a flowmeter attached. There were significant differences in larvae densities between pre and post dam closure for several species. Also, there were significant differences between the pre and post-closure periods for densities of migratory and non-migratory species, and between sampling sites. These findings indicate decline in densities and number of taxa caught after the closure of the dam. Larvae of migratory species, formerly common in the entire study area, were registered only in points influenced by the non dammed rivers (such as the Ivinheima River), indicating that the closure of Porto Primavera caused negative impacts on fish reproduction downstream of the dam.
RESUMO.O objetivo deste estudo foi identificar os principais processos (locais e/ou regionais) que influenciam a composição e a estrutura das assembléias de peixes em reservatórios do Estado do Paraná. Foram amostrados seis reservatórios (Capivari, Guaricana, Alagados, Fiú, Mourão e Rio dos Patos). As coletas foram trimestrais (de julho/95 a fevereiro/97 e de março/98 a fevereiro/99), com uso de redes de espera simples e tresmalhos, de diferentes malhagens, expostas por 24 horas. Todos os exemplares foram identificados, medidos, pesados e a abundância das espécies foi expressa pela captura por unidade de esforço (CPUE), dada em número (n o ind./ 1000m 2 de rede* 24h). Variáveis abióticas (processos locais) também foram medidas no momento de coleta. A análise de correspondência com remoção do efeito do arco (DCA) e a análise de componentes principais (PCA) foram utilizadas para sumarizar os dados de abundância e abióticos, respectivamente. Os escores dos eixos dessas análises foram utilizados para avaliar a relação entre os fatores abióticos (locais e regionais) e a estrutura das assembléias de peixes. Os processos regionais parecem ser os principais responsáveis pela composição e, conseqüentemente, pela estrutura das assembléias de peixes nos reservatórios.Palavras-chave: processos locais e regionais, assembléias de peixes, reservatórios, Estado do Paraná, Brasil.ABSTRACT. Influence of local and regional processes on fish Assemblager in reservoirs of Paraná State, Brazil. The aim of this study was to identify the main processes (local and/or regional) that influence in the composition and structure of fish assemblages in reservoirs located in the state of Paraná. Six reservoirs were sampled (Capivari, Guaricana, Alagados, Fiú, Mourão and Rio dos Patos). The samples were quarterly taken from July/95 to February/97 and March/98 to February/99 using gillnets and trammel nets of different mesh sizes set for 24 hours. The abundance was indexed by the catch per effort in number (No. ind./ 1000m 2 net* 24 hs). All fishes collected were identified, measured and weighted. Some abiotic variables (local process) were measured during the samples. The detrended correspondence analysis (DCA) and the principal components analysis (PCA) were applied to summarize abundance data and abiotic variables, respectively. The scores of the axis retained for interpretation in both analyses were used to assess the relation between abiotic variables (local and regional) and fish assemblage structure. The regional processes appeared to exert strong influence on the composition and, consequently, on the structure in the reservoirs of fish assemblage.
Um dos problemas de maior relevância e complexidade na avaliação da biologia pesqueira é a relação entre estoque e recrutamento. O termo recrutamento é referido, neste estudo, como a abundância da primeira classe etária, na qual uma coorte pode efetivamente ser estimada, constituindo-se em um processo complexo, determinado por fatores dependentes e independentes da densidade. Normalmente a análise estoque-recrutamento é resultante da observação da relação entre os tamanhos do estoque reprodutor e o número de recrutas produzidos. Existem representações sugeridas para expressar essa relação, dentre as quais estão os modelos de Beverton e Holt, Ricker e Shepherd. Neste trabalho, esses modelos foram ajustados para as populações de Serrasalmus marginatus e S. maculatus, do rio Baía, por meio de procedimento não-linear. O objetivo foi determinar o melhor modelo para a relação estoque-recrutamento e os principais fatores envolvidos. A competição pareceu ser o fator limitante ao recrutamento, sendo os modelos de Shepherd (S. marginatus) e de Ricker (S. maculatus) os mais adequados.
A paradigm is characterized as a network of conceptual, instrumental, and methodological commitments that guides the direction and methodology of scientific research. Thus, a paradigm defines what should be studied, what questions should be asked, what tools should be used, and what rules should be followed in interpreting results. The aim of this paper is to analyze how fisheries management emerged and developed in Brazil, considering that science's progress as a series of paradigms. Management actions related to reservoir fishery are not frequent in Brazil and, when applied, they did not generate good results, because they usually were based on poor technical and scientific information or in paradigms developed in the temperate region (North America). Fish passages (ladders) were the first attempt to minimize the impacts of damming, followed by regulation of fishery and stocking programs. However, it seems that the paradigm that led the researches (imported from the United States) was not appropriated for reservoir management in most Brazilian reservoirs. We agree that some other reasons contributed in some extension to the failure of management actions: i) inadequacy and insufficient data availability; ii) inappropriate approach used to perform management; iii) absence of monitoring studies; iv) policy inadequacies; and v) deficiencies in the integration among the hydroelectric companies. Recently, hydroelectric companies started to develop research in basic limnology and fish, in order to improve data quality to better support reservoir fishery management actions. We suggest that this situation is happening or maybe happened in other countries in South America and other parts of the world.
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