Hersília Santos

Swimming performance of the migratory Neotropical fish Leporinus reinhardti (Characiformes: Anostomidae)

The fishways built in Latin America were mainly based on those used in the northern hemisphere for passing salmonids upstream. However, the swimming capacity in terms of speed and endurance is a major factor concerning the design of a fishway, and this information is not available for migratory neotropical fish species. Therefore, studies on swimming performance of neotropical species is fundamental. The aim of this study was to estimate the critical, sustained and prolonged speeds for the piau-tres-pintas Leporinus reinhardti, and to evaluate the influence of water temperature on the swimming performance of the species. Variable (increasing) and fixed velocity tests were performed in a respirometer. When compared to other species whose critical speed data are available, the piau showed higher speeds, for a given total length. Fatigue times per prolonged speed class were estimated as well as prolonged speed per fatigue time class. The changing point from sustained to prolonged swimming was estimated to occur approximately at a speed of seven body-lengths per second (1.12 m/s for an individual with 16 cm total length: the first maturation length). In spite of the great swimming performance of piau, the adoption of efficient directives in fishway projects to allow the passage of neotropical ichthyofauna, will depend on a more detailed analysis of the swimming capacity of different species.

Changes in the flood regime of São Francisco River (Brazil) from 1940 to 2006

Flow regulation causes various environmental impacts in the downstream reaches of impounded rivers. The São Francisco River (SF) basin is Brazil’s third most important watershed. Several dams have been built in its course in the last four decades, mostly for flow regulation and hydropower generation. This paper presents an evaluation of historical changes in the flood regime. Three regions of the SF River basin, which are under the influence of different levels of regulation, were studied: the lower, middle, and upper SF River. The components of magnitude, frequency, and duration of floods were quantified for each region from 1940 to 1960 (prior to the construction of the first dam) and from 1986 to 2006 (after the last dam). The results have shown the inexistence of big floods in the downstream areas, decreasing durations of small floods as well as significant changes in the annual seasonality of floods. Reductions in the flood frequency were verified in all stretches, even in non-regulated systems, such as the lower Velhas River. The climate variation, which occurred in both period, was not able to explain the changes in the flood regime of São Francisco River; therefore, dams and other anthropogenic activity are the main factors promoting the temporal variability of streamflows in the São Francisco basin.

Reynolds shear-stress and velocity: positive biological response of neotropical fishes to hydraulic parameters in a vertical slot fishway

Interrupcoes em rios, como as causadas por barragens, provocam impactos negativos sobre as comunidades aquaticas e as especies migratorias de peixes sao diretamente afetadas. A fim de permitir a passagem de peixes, mecanismos de transposicao sao construidos junto a barramentos. No Brasil, apos a implantacao de leis ambientais, estas estruturas passaram a ser amplamente construidas e foram baseadas em projetos desenvolvidos na Europa e na America do Norte. Analises de mecanismos ja construidos tem mostrado grande seletividade para especies neotropicais e as demandas da diversa fauna de peixes neotropical sao apresentadas como principal desafio ao projeto de passagens para peixes. Os padroes de escoamento dentro de escadas para peixes podem explicar a seletividade destes mecanismos, mas poucos estudos detalham a resposta dos peixes as caracteristicas hidraulicas encontradas dentro das escadas. Este estudo apresenta uma analise realizada em um laboratorio onde foi construida uma escada do tipo ranhura vertical e analisados os comportamentos de duas especies neotropicais (Leporinus reinhardti e Pimelodus maculatus). O escoamento foi estudado considerando os campos de velocidade media, tensao cisalhante de Reynolds e flutuacoes de velocidades. Os individuos da especie Leporinus reinhardti apresentaram maior sucesso de passagem do que os da especie Pimelodus maculatus. Ambas as especies preferiram areas de tensao de Reynolds igual a zero. Alem disso, diferentes preferencias foram observadas para cada especie em relacao as componentes horizontais da flutuacao da velocidade.

Optimal swim speeds by respirometer: an analysis of three neotropical species

The swimming ability of neotropical fish species is an important aspect for fish ladder designs. Especially in Latin America, where fish ladders are highly selective, fish strategies to negotiate the passage should be studied focusing on target species. This paper shows the swimming ability of three neotropical species (Leporinus reinhardti, Pimelodus maculatus and Prochilodus costatus), from Sao Francisco river basin. Respirometer was employed for data collection. Regarding the critical and prolonged speeds, L. reinhardti was the fastest among the three neotropical species in relative values (body length/second). The performance of neotropical species was better when compared to critical and maximum prolonged speeds of fish species from temperate areas. Finally, regarding the experimental procedures, the optimization of swimming speed in respirometer is lower than the optimal processes obtained with free swimming in open channels.