PlanetCatfish.com

What makes things worse, imo, is that the before and after studies were done pretty close together time wise.

Because the instream reservoir is necessary for the hydropower potential of the BMHC, there is little that can be done for the conservation of rapids habitats in the upstream section. In fact, the two reservoirs currently built are projected to generate only a fraction of the full BMHC capacity.....

The sustainability boundaries approach to determining environmental flows (Richter, 2009), in which requirements are expressed as allowable percentages of deviation rather than particular volumes at given times of year, would aid in maintaining flow dynamics throughout the lower Volta Grande and lower Xingu.
Determining appropriate boundaries is a difficult process that is beyond the scope of this paper, but the roughly 80% reduction currently expected will likely leave insufficient flows for the maintenance of aquatic
diversity.

I would assume that doing another survey today vs 2014 would already be showing changes in species abundances. Doing one once the dam has been fully operational over a couple of seasons should reveal that a lot of species are completely gone or are almost impossible to find in any significant numbers.

A B S T R A C T

A recent boom in hydroelectric development in the world's most diverse tropical river basins is currently
threatening aquatic biodiversity on an unprecedented scale. Among the most controversial of these projects is the Belo Monte Hydroelectric Complex (BMHC) on the Xingu River, the Amazon's largest clear-water tributary. The design of the BMHC creates three distinctly altered segments: a flooded section upstream of the main dam, a middle section between the dam and the main powerhouse that will be dewatered, and a downstream section subject to flow alteration from powerhouse discharge. This region of the Xingu is notable for an extensive series of rapids known as the Volta Grande that hosts exceptional levels of endemic aquatic biodiversity; yet, patterns of temporal and spatial variation in community composition within this highly threatened habitat are not well documented. We surveyed fish assemblages within rapids in the three segments impacted by the BMHC prior to hydrologic alteration, and tested for dfferences in assemblage structure between segments and seasons. Fish species richness varied only slightly between segments, but there were significant dfferences in assemblage structure between segments and seasons. Most of the species thought to be highly dependent on rapids habitat, including several species listed as threatened in Brazil, were either restricted to or much more abundant within the upstream and middle segments. Our analysis identified the middle section of the Volta Grande as critically important for the conservation of this diverse, endemic fish fauna. Additional research is urgently needed to determine dam operations that may optimize energy production with an environmental flow regime that conserves the river's unique habitat and biodiversity.