Impact of dams on fisheries

Posted: 26 March 2001

The construction of large dams, such as the Aswan Dam on the Nile, can lead to big reductions in fish stocks in the connecting estuaries, according to a report by Taiwanese researcher, Chen-Tung Arthur Chen.

Dams block the down-stream transport of particulate matter which is an important source of nutrients and food for the aquatic biota. The effects, however, go far beyond the estuaries.

Take the case of the Three Gorges Dam in China. The completion of this dam on the Yangtze River is likely to reduce productivity in the largest fishing grounds in the world.

Cutting back the Yangtze River outflow by a mere 10 per cent will reduce the cross-shelf water exchange by about 9 per cent because of a reduced buoyancy effect, and, at the same time, it will cut the onshore nutrient supply by nearly the same amount. Primary production and fish catch in the East China Sea can be expected to decrease proportionately.

From a global perspective, approximately 40 per cent of the fresh water and particulate matter entering the oceans are transported by the 10 largest rivers and this is in the form of a buoyant plume on the open shelves. These shelves also face diminished fish production when damming reduces freshwater outflow.

Source: International Geosphere-Biosphere Programme: Global Change Newsletter, December 2000.