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Hippo Overcrowding Blamed for Fish Deaths
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| The Olifants River was one
of the largest continuously flowing rivers in South Africa, but at this time
of year it is reduced to a series of pools in the Kruger National Park (KNP),
kept alive by water released from the Phalaborwa Barrage.
As a result, hippos living in the river are forced into the ever dwindling pools which they share with the fish. Hippos are forced to congregate in the remaining pools of water. In the pool where the fish died, Dr Thomas Gyedu-Ababio, the KNP's aquatic biodiversity conservation manager, has found almost 100 hippos in less than 500 metres. According to Gyedu-Ababio this has caused many fish to die from oxygen starvation. Gyedu-Ababio found at least 500 dead fish on the banks of a pool in what remains of the Olifants River when he visited the site recently. They were mostly catfish, yellowfish and tilapia. In a reversal of their normal behaviour, Gyedu-Ababio said: "The hippos ran out of the water when they saw people," as there was not enough water in the pool to cover them. The hippo have been living and defecating in the pools, producing an excessive quantity of dung that was now decomposing. At normal levels the dung is usually associated with providing much needed nutrients to aquatic ecosystems. |
However, at these levels, the decomposition
removes oxygen from the water, causing the fish to suffocate. Fish jumping
out of the water in other pools was also a sign of oxygen shortage.
The Phalaborwa Barrage is required to release water for the ecological needs of the Olifants River, but also has to provide water for human use. Gyedu-Ababio said the flow out of the barrage for several days prior to the fish deaths was so low that the gauging weir in the park could not accurately measure it. The barrage has very limited water storage, as almost 90% of the dam is occupied by silt. It is estimated that there is only enough water in the barrage when it is full for two to three days' water supply. The silt in the barrage is to be the subject of an environmental study which went out to tender in February. The tender has yet to be awarded, the Lepelle Northern Water authority said. The release of large volumes of silt-laden water from the barrage has previously caused fish deaths in the Olifants. The silt is largely derived from soil erosion caused by poor agricultural practices further upstream in the Olifants River, in Sekhukhuneland.
Sources: News 24 (of
South Africa - online) - 30 August 2005
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