Thursday, June 16, 2011

River Invaders

The name Asian carp is used to describe four different species of carp: grass carp, bighead carp, silver carp, and black carp. These fish were introduced in the United States in the 1970s and since that time have spread rapidly. At least one species of Asian carp is found in every state except Alaska, Maine, Montana, Rhode Island, and Vermont. They pose a major ecological threat to native aquatic wildlife and river ecosystems, as well as a significant economic threat to commercial fisheries.

All Asian carp species are native to large rivers in eastern Asia and were introduced in the U.S. to “improve” water quality. Some species, such as the grass carp, were introduced to control nuisance plant species because they eat algae and other aquatic plants. Other species, such as the black carp, eat mussels and snails and were introduced to control disease carrying invertebrates in aquaculture ponds.

From aquaculture, Asian Carp were introduced into American rivers by illegal and intentional release, or by accidental escapes from river flood waters reaching aquaculture ponds. Once in the wild, they pose several threats to the ecosystem. Grass carp consume enormous amounts of plants. Their voracious appetite robs native fish and invertebrates of their food source. Large quantities of carp waste degrade water quality.

The two species threatening the Great Lakes are the silver and bighead carp. Millions of dollars have been spent on electric barriers, cameras, and other monitoring equipment attempting to protect the lakes. Asian carp have already caused extensive environmental and economic damage in the Mississippi and Missouri River basins. Many people have had to abandon their fishing grounds because of the presence of carp. This threatens a 7 billion dollar per year commercial and recreational fishery in the Great Lakes. Silver carp can also harm humans. When startled by boat motors, the fish (which can weigh up to 60 lbs!) leap out of the water, causing potential injury or fatality to people.

There is now concern that the extent of Asian carp’s range has increased. The flooding of the Mississippi and Missouri rivers this year may have transported some of these fish into lakes and tributaries where there are no established carp populations.

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