João Dirço Latini

Effects of River Impoundment on Ecosystem Services of Large Tropical Rivers: Embodied Energy and Market Value of Artisanal Fisheries

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.

Fish colonization of artificial reefs in a large Neotropical reservoir: material type and successional changes

Artificial reefs have barely been used in Neotropical reservoirs (about five studies in three reservoirs), despite their potential as a fishery management tool to create new habitats and also to understand fish ecology. We experimentally assessed how reef material (ceramic, concrete, and PVC) and time modulated fish colonization of artificial reefs deployed in Itaipu Reservoir, a large reservoir of the mainstem Paraná River, Brazil. Fish richness, abundance, and biomass were significantly greater in the reef treatments than at control sites. Among the experimental reefs, ceramic followed by the concrete treatments were the materials most effectively colonized, harboring the majority of the 13 fish species recorded. Although dependent on material type, many of the regularities of ecological successions were also observed in the artificial reefs, including decelerating increases in species richness, abundance, mean individual size, and species loss rates with time and decelerating decreases of species gain and turnover rates. Species composition also varied with material type and time, together with suites of life history traits: more equilibrium species (i.e., fishes of intermediate size that often exhibit parental care and produce fewer but larger offspring) of the Winemiller-Rose model of fish life histories prevailed in later successional stages. Overall, our study suggests that experimental reefs are a promising tool to understand ecological succession of fish assemblages, particularly in tropical ecosystems given their high species richness and low seasonality.

Fish fauna disassembly after the introduction of a voracious predator: main drivers and the role of the invader's demography

The introduction of Cichla kelberi to the Rosana Reservoir (Paraná River basin, Brazil) was followed by a substantial loss of fish diversity in macrophyte patches, and this study investigated the hypothesis that C. kelberi was the driver of faunal disassembly via certain demographic dynamics (i.e. a pulse of juvenile fish). We analysed the variation in the structure of fish assemblages, the abundance of C. kelberi and habitat quality between 2003 and 2007, including time points that preceded and followed the introduction of the predator. A stepwise regression analysis showed that macrophyte biomass was positively correlated with assemblage attributes (richness and abundance), whereas C. kelberi density showed a strong negative correlation. Variables related to habitat quality were not included in the model, and exhibited little variation over the study years. As predicted, the density of small-bodied fish was negatively associated with the pulse of juvenile C. kelberi, and a tethering experiment revealed that predation pressure increased in the macrophyte patches when young C. kelberi were abundant. This study therefore obtained strong evidence supporting the hypotheses that C. kelberi caused the fish fauna disassembly and that the predator’s demography was the driver underlying the diversity loss.

Rotenone calibration of fish density and biomass in a tropical stream sampled by two removal methods

A catch-depletion method was applied using two sampling gears in three sites of a small tributary of the Corumba River (Goiás State, Brazil) in two seasons. The gears were: a double stick net (DSN) in one site and electric fishing (EF) in two sites. The calibration of both gears was performed using rotenone. EF was almost sufficient to establish a complete local species list, but DSN was not. Underestimation of calculated density (N) and biomass (B) values for DSN and EF amounted to 62 and 29%, respectively. The results of N and B obtained by EF were too imprecise to calculate secondary fish production to be applied in a field bioenergetics model. We could not conclusively prove that mean body weight of sampled populations was significantly lower for fish caught by EF, although all of these means were higher for fish collected by rotenone, at each site and on two sampling occasions.

Fish, Maringá Urban Streams, Pirapó river drainage, upper Paraná river basin, Paraná State, Brazil

The metropolitan area of Maringa, Parana state (southeastern Brazil), has many small headwater streams that are affected by urban development. Checklists of fish species in these sites are important tools to learn about the biodiversity of impacted environments. Samples were taken every two months from July 2007 to June 2008 in three different sites along 10 small headwater streams in Maringa city within a gradient of urbanization. A total of 38 fish species ascribed to six orders, 12 families, and 27 genera were collected, including six non-native species, and 14 that are probably new species.

Morphological description of larvae of the Mapará Hypophthalmus edentatus (Spix) (Osteichthyes, Hypophthalmidae) in the Itaipu reservoir (Parana River, Brazil)

The ontogenetic aspects of larvae of Hypophthalmus edentatus (Spix, 1829) from the ichthyoplankton samples collected in the Itaipu reservoir between March 1988 and April 1990 were analysed. Sample were caught by 0.5 mm mesh conic-cylindrical plankton net. Larvae of H. edentatus were identified and described as Siluriforms from the morphological and morphometric development series. They have a small to medium-sized head, long body, small eyes, little pigmentation, mandibular barbules and 53 to 56 myomeres. High values obtained with correlation coefficient (r > 0.97; p < 0.001) show that growth was proportional in different parts of the body.

A barrier to upstream migration in the fish passage of Itaipu Dam (Canal da Piracema), Paraná River basin

The majority of the fish passages built in the Neotropical region are characterised by low efficiency and high selectivity; in many cases, the benefits to fish populations are uncertain. Studies conducted in the Canal da Piracema at Itaipu dam on the Parana River indicate that the system component designated as the Discharge channel in the Bela Vista River (herein named Canal de desague no rio Bela Vista or CABV), a 200 m long technical section, was the main barrier to the upstream migration. The aim of this study was to evaluate the degree of restriction imposed by the CABV on upstream movements of Prochilodus lineatus and Leporinus elongatus, Characiformes. Fish were tagged with passive integrated transponders (PIT tags) and released both downstream and upstream of this critical section. Individuals of both species released downstream of the CABV took much more time to reach the upper end of the system (43.6 days vs. 15.9 days), and passed in much lower proportions (18% vs. 60.8%) than those tagged upstream of this component. Although more work is needed to differentiate between fishway effects and natural variation in migratory motivation, the results clearly demonstrate passage problems at the CABV.

The coexistence of fish species in streams: relationships between assemblage attributes and trophic and environmental variables

Diet overlap and niche breadth are well-known species traits from trophic ecology that can assist in explaining how species interact and coexist as well as the ecological mechanisms that influence biodiversity. In the present study, we analyzed the relationships between these trophic variables and indicators of resource availability with some attributes of fish assemblages (species richness, Shannon diversity index, evenness, density and individual body size). The physical and chemical characteristics of the biotopes (topography, water quality and conservation of slopes) were examined to identify possible patterns. Monthly sampling using electrofishing was conducted in 2003 along five streams located in the Cuiabá River watershed. The relationships between environmental variables and attributes of fish assemblages were evaluated using Spearman correlation. Species richness and abundance varied among streams, with higher values (54 and 82 species) found in low-gradient streams that drained small swampy areas discharging in Cuiabá River. Diet overlap showed significant and negative correlations with species richness, the diversity index, abundance, variation in body size and food availability and positive correlations with evenness and niche breadth. Environments that had greater food availability had a reduced variety of food items (smaller amplitude) and distinct values in terms of dietary overlap. Nevertheless, to explain resource partitioning in a fish assemblage (overlap), it is necessary to consider food availability and niche breadth (degree of trophic specialization) beyond the interaction of these variables with species richness and density. In conclusion, high diversity and abundance values were strongly associated with a high degree of trophic specialization (low amplitude of trophic niche) and a small degree of overlap in the diet.

‘Three seine nets’ sampling applied to the littoral zone of two Brazilian tropical rivers with reduced velocity (Brazil)

Abstract Three seine nets (TSN method) laid simultaneously from the bank to form concentric semicircles (enclosing an area of 350 m 2 ) and hauled one after the other were employed for the removal fishing technique in littoral zones with reduced velocity in the Parana River catchment. Fish density was estimated using the Zippin maximum likelihood method. The efficiency of this TSN method, estimated by two different indexes was not diminished by the size of the populations, but was limited by the kind and amount of obstacles on the bottom (submerged macrophytes, branches, mud) and the habitat preferences of the fish taxa. TSN was found to give best results for pelagic fishes, slightly less good for bentho-pelagic, and less good again for benthic ones, although it was not altogether unsatisfactory for quantitative research on fish populations.