No abstract

Applying the ecosystem services concept to conservation initiatives or in managing ecosystem services requires understanding how environmental impacts affect the ecology of key species or functional groups providing the services. We examined effects of river impoundments, one of the leading threats to freshwater biodiversity, on an important ecosystem service provided by large tropical rivers (i.e., artisanal fisheries). The societal and economic importance of this ecosystem service in developing countries may provide leverage to advance conservation agendas where future impoundments are being considered. We assessed impoundment effects on the energetic costs of fisheries production (embodied energy) and commercial market value of the artisanal fishery of the Paraná River, Brazil, before and after formation of Itaipu Reservoir. High-value migratory species that dominated the fishery before the impoundment was built constituted a minor component of the contemporary fishery that is based heavily on reservoir-adapted introduced species. Cascading effects of river impoundment resulted in a mismatch between embodied energy and market value: energetic costs of fisheries production increased, whereas market value decreased. This was partially attributable to changes in species functional composition but also strongly linked to species identities that affected market value as a result of consumer preferences even when species were functionally similar. Similar trends are expected in other large tropical rivers following impoundment. In addition to identifying consequences of a common anthropogenic impact on an important ecosystem service, our assessment provides insight into the sustainability of fisheries production in tropical rivers and priorities for regional biodiversity conservation.

Physical, chemical, and biological gradients along reservoirs are clear and exhibit marked spatial and temporal variations. These variations are rarely quantified and may produce spatial gradients in fisheries. We analyzed trends in total yield and gradients and relationships between catch-per-unit-effort (CPUE) and some characteristics of the fishery in the large Neotropical Itaipu Reservoir in Brazil. Data on the artisanal fisheries were collected over an 11-year period (414 213 daily trips). Annual yield (especially after 1993) and CPUE (annual total and for each species) decreased over the studied period. A clear longitudinal pattern in the CPUE values for the main species was recognized, and this pattern presented a significant relationship with the type of gear and characteristics of the vessels used in the fisheries. The decline in yield and CPUE is apparently due to changes in trophic state, as well as to the construction of reservoirs upstream from the region and to overfishing. It is clear that the spatial zonation influenced fish species distribution along the reservoir and, therefore, the fishery. We conclude that for this large Neotropical reservoir, spatial gradient cannot be ignored in management plans, and this appears to be true for any reservoir that exhibits zonation.Résumé : Il y a des gradients physiques, chimiques et biologiques bien marqués le long des réservoirs et ils présentent de nettes variations dans l'espace et dans le temps. Ces variations sont rarement mesurées quantitativement, bien qu'elles puissent produire des gradients spatiaux dans les pêches. Nous avons analysé les tendances du rendement total et des gradients, ainsi que les relations entre la capture par unité d'effort (CPUE) et quelques caractéristiques de la pêche dans le grand réservoir néotropical Itaipu (Brésil). Les statistiques sur les pêches artisanales ont été compilées sur une période de onze années (414 213 sorties journalières). Le rendement annuel (surtout après 1993) et la CPUE (totale annuelle et spécifique à chaque espèce) ont décliné au cours de la période d'étude. Il existe un net patron longitudinal de CPUE des espèces principales qui est en corrélation significative avec le type d'engin de pêche et les caractéristiques des bateaux utilisés pour la pêche. Le déclin du rendement et de CPUE est apparemment dû à des changements d'état trophique, mais aussi à la construction de réservoirs en amont et à la surpêche. Il est clair que la zonation spatiale influence la répartition des poissons le long du réservoir et, par conséquent, la pêche. En conclusion, on ne peut négliger le gradient spatial dans les plans d'aménagement de ce grand réservoir néotropical; la même contrainte s'impose à tout réservoir qui présente de la zonation. [Traduit par la Rédaction]Okada et al. 724

–  River–floodplain systems present intense temporal variations in physical, chemical and biological factors. These variations are closely related to alterations in water levels, which have been attributed to the flood pulse. As several species are strictly related to the flood pulse to fulfil their life cycle, the pulse may be seen as a dispersal mechanism of species onto a floodplain. In this study, we determine how dam construction influenced the persistence of Prochilodus lineatus population, a large migratory fish species from the upper Paraná River floodplain. Data used were collected in two distinct periods, from April 1992 to March 1993 and from January 1999 to December 2001. Fish were collected using seining nets in six (monthly in the first period) and seven (quarterly in the second period) isolated lagoons. The fraction of occupied lagoons was high in the first period (higher than 0.65), when flood was intense. However, in the second period, when the flood pulse did not happen or was short, the fraction of occupied lagoons sharply decreased over time (from 0.85 to 0.22). For the first period, no model fitted to data, but for the second period, a negative linear model (named drought‐dependent model) presented good fit (r2 = 0.97). Therefore, it is possible to infer that long and intense flood pulses are important to maintain the persistence of P. lineatus populations in the floodplain. The artificial control of water levels prompted by dams disrupts this dynamic, reducing persistence to critical levels.

In eleven sites on two small tributaries of the Parand River (North-West Parand State)| 6 .8 and 4 .0 km in length| 1263 fish specimens of 28 taxons and 14 families were collected using electrofishing . Up to twelve years ago the catchments of the two rivers were covered by tropical jungle ; this has now been replaced by pasture and arable fields . Mean diversity indices of Simpson and Shannon indices were close to 0 .6| which would indicate that human impact affected fish populations although the river beds have retained their original shape| except cleared of riparian trees . Despite their close location (about 18 km)| the two streams differed from each other in their fish faunal composition . The distinctive nature of the fish communities in the two streams was a result of: conductivity| pH| also hiding places| riparian vegetation| submerged macrophytes and depth and width of the rivers .