Protecting the downstream migration of salmon smolts from hydroelectric power plants with inclined racks and optimized bypass water discharge.

The sustained development of hydropower energy in the last century has caused important ecological impacts, promoting recent advances in efficient mitigation measures to be implemented in existing and future hydropower plants. Although upstream fish migration has been largely addressed with the development of fish-pass infrastructures, downstream passage solutions are often missing or inefficient, strengthening the need for their improvement and efficiency assessment. The efficiency of horizontally inclined (26°) low bar spacing racks associated to a bypass was assessed using salmon smolts radiotelemetry along three successive hydropower plants (HPP) in the Ariège River (southern France). In average, nearly 90% of the smolts were successfully protected by the racks and rapidly guided to the bypass, within few minutes in most cases. Furthermore, we detected a significant positive influence of the bypass discharge (Qbp% expressed as the proportion of concurrent HPP discharge) on the probability of successful bypass passage, reaching 85% of successful passage with a Qbp% of only 3%, and more than 92% when the Qbp% exceeded 5%. The probability of bypass passage without hesitation (e.g. passage within the first 5 min) also increased with Qbp%, and reached 90% with 5% of Qbp%. Passage without hesitation was especially detected on the site having larger bypass entrances and transversal currents, providing better guidance into the bypass. High-efficiency results of inclined racks yielded with reduced Qbp% confirmed their relevance to mitigate some of the HPP ecological impacts, re-establishing safe downstream salmon migration with lower impact on energy production than older less efficient solutions.

Local-scale species-energy relationships in fish assemblages of some forested streams of the Bolivian Amazon.

Productivity (trophic energy) is one of the most important factors promoting variation in species richness. A variety of species-energy relationships have been reported, including monotonically positive, monotonically negative, or unimodal (i.e. hump-shaped). The exact form of the relationship seems to depend, among other things, on the spatial scale involved. However, the mechanisms behind these patterns are still largely unresolved, although many hypotheses have been suggested. Here we report a case of local-scale positive species-energy relationship. Using 14 local fish assemblages in tropical forested headwater streams (Bolivia), and after controlling for major local abiotic factors usually acting on assemblage richness and structure, we show that rising energy availability through leaf litter decomposition rates allows trophically specialized species to maintain viable populations and thereby to increase assemblage species richness. By deriving predictions from three popular mechanistic explanations, i.e. the 'increased population size', the 'consumer pressure', and the 'specialization' hypotheses, our data provide only equivocal support for the latter.

[Body size, ecological tolerance and potential for water quality bioindication in the genus Anacroneuria (Plecoptera: Perlidae) from South America]. / Tamaño corporal, tolerancia ecológica y potencial de bioindicación de la calidad del agua de Anacroneuria spp. (Plecoptera: Perlidae) en América del Sur.

Knowledge about the biology and ecology of neotropical aquatic taxa is crucial to establish general ecological rules and water protection systems. Based mainly on published data, the present work shows the following biological and ecological characteristics of Anacroneuria species (Klapálek 1909): (a) the wide range of environmental conditions of rivers where Anacroneuria species occur, (b) species number decreases along an increasing elevation gradient, (c) body size increases in relation to the maximum altitude of occurrence, (d) altitudinal range increases with body size, (e) there is a constant relationship between male and female body size, and finally, (f) larger females lay larger eggs. In temperate countries, the family Perlidae in general, and the genus Anacroneuria in particular, are viewed as excellent water quality indicators. We suggest that, considering the complexity of the group's ecology in South America, it should not be automatically considered an excellent bioindicator in the Neotropical region.

Tamaño corporal, tolerancia ecológica y potencial de bioindicación de la calidad del agua de Anacroneuria spp. (Plecoptera: Perlidae) en América del Sur / Body size, ecological tolerance and potential for water quality bioindication in the genus Anacroneuria (Plecoptera: Perlidae) from South America

Knowledge about the biology and ecology of neotropical aquatic taxa is crucial to establish general ecological rules and water protection systems. Based mainly on published data, the present work shows the following biological and ecological characteristics of Anacroneuria species (Klapálek 1909): (a) the wide range of environmental conditions of rivers where Anacroneuria species occur, (b) species number decreases along an increasing elevation gradient, (c) body size increases in relation to the maximum altitude of occurrence, (d) altitudinal range increases with body size, (e) there is a constant relationship between male and female body size, and finally, (f) larger females lay larger eggs. In temperate countries, the family Perlidae in general, and the genus Anacroneuria in particular, are viewed as excellent water quality indicators. We suggest that, considering the complexity of the group's ecology in South America, it should not be automatically considered an excellent bioindicator in the Neotropical region.