apistomaster wrote:There are many engineering features which can help mitigate down stream effects of dams and to account for the migrating species of large Characins which would not cost much.
There are possible mitigation efforts yes, but my impressions is that the entire problem has been completely ignored. There is no species list for Xingu and according to the international biodiversity databases the Xingu is extremely species-poor, with just a single endemic species!; the EIA completely ignored aquatic lifeforms; I've seen no environmental organization show public concern for the aquatic species of the Xingu; and every single piece of news I could google were about the displacement of native tribes (important, but to my mind less important than the extinction of double digits of unique vertebrate species).
From my vantage point, 1000 kilometers from the Xingu, it seems there are no mitigation efforts for the fish because politically speaking
the issue doesn't exist. It's been completely swept under the rug.
Behind the impoundments, in the resulting reservoirs, there are many other problems which are more intractable to engineering and management fixes.
The first one will be that the water in the dam turns anoxic while it is filled, due to the vast amounts of rotting vegetation. There are eye-witness accounts of how there were literal "heaps" of dead loricariidae,
Teleocichla, and other rheophilic species killed by the rotten water when the Tucurui dam was filled. Then when the dam starts producing electricity, the rotten, oxygen-free and hydrogen sulphide-rich, water moves like a "plug" down river, killing sensitive fish for miles downstream.
Breeding cycles of many local fish are disrupted partly because they're no longer able to migrate, but also because there no longer will be any seasonal change in flow.
In the dam itself there will for 5-10 years be a fishery bonanza, due to opportunistic and introduced fish species taking advantage of the enormous amounts of plankton and insect larvae eating all the rotting vegetation.
Then, 25-30 years after the dam was built, it'll typically start silting up and isn't producing much electricity any more; the downstream riverbed is also silting up, resulting in floodings; the fishery in the dam declines sharply; pollution, especially mercury poisoning, becomes a problem around the dam; the bulk of the remaining fishery depends on introduced species; and of the fish species originally found in the area only 20-40% remain (most in tiny refugia, and the commercial ones depend on captive breeding programmes to not go extinct).
At this point, the people who brought you the dam have long since moved on to making new fortunes from new dams in new biodiversity hotspots.
Does anyone know what the projected lifespan of the Xingu dam is? I've been unable to find an estimate.