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News – Science: Fish poison in low doses won’t damage ecology

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Original Post Date: 2009-01-22 Time: 03:00:07  Posted By: Jan

CapeNature could use the controversial fish poison Rotenone to kill alien fish in four selected rivers without significant harm to the river or land ecosystem.

This was the finding of the environmental impact assessment (EIA) released on Wednesday for public comment. The proposal has yet to be approved by the authorities.

The proposed use of Rotenone has caused widespread alarm because uncontrolled use in the past has led to serious ecological harm to river systems, with high doses of the poison killing off almost everything in the water.

But the specialist studies have found that if used in a controlled manner in low doses according to an approved environmental management plan, the poison would be an acceptable way of getting rid of alien fish, chiefly trout and bass.

The report says if no action is taken to eradicate alien fish, some species of indigenous fish in the Cape Floral Region will become extinct.

It says Rotenone, a natural poison from the root of a South American tree, has been used “widely and successfully” on a much greater scale than that proposed by CapeNature.

The specialists found using nets or electric fishing to get rid of alien fish would work only in the upper section of the Krom in the Cederberg.

Where this would not be feasible, the only means of ensuring the complete removal of alien fish would be the use of fish poison.

The poison will also kill all indigenous fish and some of the macroinvertebrates like dragonflies, mayflies and beetles.

The time the river takes to recover will depend on whether it can be repopulated naturally or artificially, or by removing organisms and storing them.

The poison would have a “negligible” impact on land ecology, the report said, and different macroinvertebrates had widely differing tolerances of Rotenone, so the severity of harm would vary greatly between species.

The poison would affect some species of frogs and tadpoles, none of them threatened.

The rivers where sections would be poisoned are the Suurvlei, Rondegat and Krom in the Cederberg and the Krom in the Eastern Cape.

Water birds, otters and snakes in these four rivers are not likely to be affected as they “lack an effective mechanism for transporting Rotenone into the bloodstream”, and can tolerate doses several times higher than those used to kill fish.

The report recommends that some indigenous fish be caught and kept in pools before the poison is used.

The EIA, with public comment, is to be submitted to the authorities next month.

    • Source: http://www.iol.co.za/index.php?art_id=vn20090122060109362C513429