Common Carp - Introduction Into Other Habitats

Introduction Into Other Habitats

Common carp have been introduced, sometimes illegally, to most continents and some 59 countries. Due to their fecundity and their feeding habit of grubbing through bottom sediments for food, they are notorious for altering their environments. In feeding, they may destroy, uproot, disturb and eat submerged vegetation, causing serious damage to native duck, such as canvasbacks, and fish populations. Similar to the grass carp, the vegetation they consume is not completely digested, and rots after excretion, raising the nutritional level of the water and causing exsessive algae growth. They destroy nests of other fish and eat their eggs, reducing their numbers significantly.

Efforts to eradicate a small colony from Tasmania's Lake Crescent without using chemicals have been successful, but the long-term, expensive and intensive undertaking is an example of both the possibility and difficulty of safely removing the species once it is established. One proposal, regarded as environmentally questionable, is to control common carp by deliberate exposing them to carp-specific Koi herpes virus with its high mortality rate. In Utah Lake, the common carp's population is expected to be reduced by 75% by using nets to catch millions of them and either give them to people who will eat them or processing them into fertilizer. This, in turn, will give the native June sucker a chance to recover its declining population. Another method is by trapping them in tributaries they use to spawn with seine nets and exposing them to rotenone. This method has shown to reduce their impact within 24 hours and greatly increase the native vegetation and desirable fish species. This also leaves the baby carp easily preyed upon by native fish.

In Australia, enormous anecdotal and mounting scientific evidence indicates introduced carp are the cause of permanent turbidity and loss of submergent vegetation in the Murray-Darling river system, with severe consequences for river ecosystems, water quality and native fish species. In Victoria, Australia, common carp has been declared as noxious fish species, the quantity a fisher can take is unlimited. In South Australia, it is an offence for this species to be released back to the wild. An Australian company converts common carp into plant fertilizer.

Common carp were brought to the United States in 1831. In the late 19th century, they were distributed widely throughout the country by the government as a food-fish, but they are no longer prized as a food-fish. As in Australia, their introduction has been shown to have negative environmental consequences, and they are usually considered to be invasive species. Millions of dollars are spent annually by natural resource agencies to control common carp populations in the United States.

Common carp are believed to have been introduced into the Canadian province of British Columbia from Washington. They were first noted in the Okanagan Valley in 1912, as was their rapid growth in population. Carp are currently distributed in the lower Columbia (Arrow Lakes), lower Kootenay, Kettle (Christina Lake), and throughout the Okanagan system.