Wetlands Research, Inc. HW

The Common Carp Threat

The Common Carp was introduced to North America by the U.S Fish Commission in the late 1800s as a cheap source of protein. Due to the culinary preference for this species by the immigrants of the time, the Fish Commission encouraged the cultivation of Carp. However, the Carp often escaped the fish farms during flood events. They prospered in the wild due to the lack of native predators and the abundance of suitable habitat. The Carp population grew rapidly, dominating low gradient, soft bottom wetlands, lakes and streams. Carp represent 90 percent of the fish biomass in the aquatic systems to be used in the proposed research project. Carp do significant harm to the native, aquatic ecosystems of North America (e.g., wetlands, lakes, streams, and rivers), affecting other aquatic organisms and humans alike. In their search for food, they scarify the benthos and, in the process, uproot the aquatic plants which provide numerous ecosystem services. These plants slow and thereby store flood waters, and provide stable substrate for the critical microbial communities, which process aquatic contaminants such as excess nitrogen and phosphorous. The plants also sequester carbon and sediment, provide habitat for a wide range of animals, and support biodiversity. The Carp’s activities create an unstable aquatic environment that is turbid, unsuitable for essential microbial and plant propagation and lead to the transmission of unwanted extreme flows and contaminants downstream. The presence of Carp, in part, is responsible for the hypoxic conditions in the Gulf of Mexico because they disrupt the growth of the microbial populations that are responsible for denitrification.

Capture and Removal

It may be possible to install barriers to upstream migration in the spring and allow selective removal of Carp. Carp are known to migrate downstream in the late fall, seeking deep waters to avoid freezing during the winter. In the spring, at water temperatures above 60 degrees Fahrenheit, Carp migrate upstream seeking grassy, inundated floodplains and wetlands in which to spawn. Two general methods can be used to impede upstream Carp migration in the spring. One method involves the use of block nets around deep pools that act as winter traps which can be drained and seined. The second method uses block nets with female Carp emitting pheromones to attract male Carp. The attracted Carp are then removed. In the spring, the caged fecund females will be placed upstream of trap nets and the incoming fish directed by a fine meshed tube into a steel basket that can be lifted out of the water so that the native fish can be separated and returned to the river while the Carp are sold, buried, or left for scavengers. The proposed techniques and devices that are described below will be tested as possible means for controlling the Common Carp and its deleterious effects on the physical environment, other aquatic organisms and humans. As mentioned before, this species is not native to North America and has few or no native predators once it reaches six to eight months old. As a result, Carp tend to dominate their aquatic niche. The objective of this research project is to explore alternative methods to reduce Carp densities and to examine ecosystem level responses to the reduced densities.