Carolina V. Minte-Vera

Structure of fish assemblages along spatial gradients in a deep subtropical reservoir (Itaipu Reservoir, Brazil-Paraguay border)

SynopsisWe assessed the structure of the fish assemblages in the Itaipu Reservoir (Paraná River, Brazil-Paraguay) along a longitudinal or river-dam gradient (composed of riverine, transitional and lacustrine zones) and transversal or upstream–downstream gradients of the tributaries (composed of lotic and lentic stretches of tributaries and reservoir shores). We sampled stations distributed along the environmental gradients quarterly during two years. We caught mostly piscivorous, detritivorous and insectivorous fishes. The structure of the whole fish assemblage both at the regional spatial scale and at the zones of each gradient was significantly non-random according to null models and ordination analysis. When the assemblage was broken into groups, the piscivores and detritivores as well as the predators and prey showed significant non-random structure whereas the insectivores, omnivores, herbivores, benthophages and mud-eaters showed random structure. The first groups are those that had more species and the last mentioned are those with fewer species. The tributaries varied more in composition among themselves than the reservoir shores, showing a high heterogeneity in the transversal gradient. The most widespread species was the introduced piscivore Plagioscion squamosissimus. The loricariids were most abundant in the lotic and lentic stretches of the tributaries. We also observed temporal variability in species composition, mainly in the reservoir shores possibly due to the influence of the upstream floodplain on the migratory fish that periodically use the reservoir as feeding habitat. In the tributaries, the temporal changes were less predictable. A combination of habitat preferences and interactions among species, especially predator–prey relations, might be responsible for the observed structure patterns.

Feeding ecology of two sympatric species of large-sized groupers (Perciformes: Epinephelidae) on Southwestern Atlantic coralline reefs

A garoupa e o badejo-verdadeiro sao predadores oportunistas de grande porte, com estrategia de emboscada, comumente encontrados em recifes tropicais do Atlântico Sul. A dieta das duas especies foi investigada, avaliando influencias ontogeneticas, espaciais e temporais, assim como a sobreposicao no uso de recursos entre estes dois predadores co-orrentes no Banco dos Abrolhos, Brasil. Decapodes e peixes foram os principais itens alimentares de Epinephelus morio, enquanto que os peixes foram as principais presas de Mycteroperca bonaci. Ambas as dietas foram significativamente influenciadas pelo tamanho corporal e habitat, mas apenas individuos menores de E. morio alimentaram-se quase que exclusivamente de crustaceos. Como as duas especies utilizam muitas presas semelhantes, a coexistencia parece ser facilitada pelo fato de E. morio se alimentar principalmente de crustaceos, particularmente do caranguejo Cronius ruber, enquanto que o badejo-verdadeiro consome relativamente poucos crustaceos e grande quantidade de peixes. Predadores como as especies estudadas podem causar efeitos indiretos na comunidade e influenciar uma grande variedade de processos ecologicos, como conexoes entre predadores de topo e intermediarios e predadores intermediarios e seus recursos.

Fishers' and scientific histories: an example of consensus from an inland fishery

In this study we tested the basic premise that fishers’ knowledge provides similar perceptions about exploited stocks to data gathered by standardised monitoring in a small-scale commercial fishery. To that end, we compared temporal trends in catch and individual size for fish species between data obtained from interviews with fishers and a 25-year dataset from a landing monitoring program in the Itaipu Reservoir (Brazil). Fishers described with accuracy changes in species composition of the catches, from large migratory species of high commercial value (common before impoundment) to migratory species of low commercial value and sedentary species following damming. Temporal trends in catches reported by fishers and documented in the landing data matched for most species. Histories diverge when absolute values are involved, such as when fishers were asked to recall their largest catch. Fishers were homogeneous in their reports, indicating that instead of individual opinions, they revealed knowledge resulting from their observation and fishery experience. Fishers can be a reliable source of information for detecting changes in catches over time, especially when large-scale habitat changes have occurred within the time scale of a fisher career. Fishers may be key partners to be considered by managers in information gathering for effective management.