By Douglas Hunter
Since their introduction in the 1960s to North America through fish farms and research facilities, Asian carp have become an environmental disaster. Having escaped Arkansas aquaculture farms, the invasive fish have established self-sustaining populations in the Mississippi River basin. Their northward migration reached a crisis point in late 2009, when Asian carp DNA was discovered in the Chicago Sanitary and Ship Canal, which links the Mississippi system with the Great Lakes.
Four different species of Asian carp are of concern, the most worrisome being the bighead, grass and silver. The black carp, which is also causing alarm, was introduced in U.S. fish farms in the early 1990s to control snail-borne parasites.
Asian carp mainly feed on plankton, algae and aquatic insects, and their voracity threatens the entire food chain. By competing with the young from other fish species, Asian carp have an impact all the way up the food chain to birds and mammals that feed on native fish. Competition for food resources also affects molluscs and puts endangered or threatened freshwater species at further risk. The black carp feeds directly on mussels and snails. Grass carp eat what it sounds like: generally aquatic plants, and plenty of them. A single adult can consume 40 percent of its body weight in a single day. This species’ destruction of plant life can radically change ecosystems.
A risk-management study by Canada’s Department of Fisheries and Oceans in 2004 determined that Asian carp were sufficiently tolerant of the northern climate to colonize the entire Great Lakes if introduced there. Both Canadian and U.S. risk- management studies have rated colonization potential as “high.” Asian carp are known to carry the Asian tapeworm and, biologists fear, could introduce other parasites and pathogens to native species.