Invasive Black Carp Now 'Sustaining on Their Own' in the Mississippi River

Black carp have successfully invaded the Mississippi River, expanding their own populations and harming native wildlife.

The invasive species from east Asia has now established itself in the Mississippi, according to a study co-authored by the U.S. Geological Survey (USGS) and published in the journal Biological Invasions.

This finding is significant, as it marks the first time that a population of black carp has been found to be established, naturally breeding and living through to adulthood, in the U.S.

"This is the most comprehensive study and the first research to provide strong evidence that they are present and sustaining on their own," Patrick Kroboth, a research fish biologist with the USGS and co-author of the study, said in a USGS statement.

Black carp, also known as the Chinese black roach, are native to rivers across China and Vietnam. They first came to the U.S. in the 1970s accidentally, as stowaways in stocks of grass carp that were being deliberately imported into the U.S. Over subsequent decades, they were also brought over for use as biological control agents to prevent the spread of the yellow grub in aquaculture ponds. Over time, possibly as a result of flooding, the fish got out into the riverways and spread across the Mississippi river basin.

The black carp have a negative impact on the other native wildlife in the Mississippi, as they readily feed on endangered and protected native mussels and snails, many of which are important algae-grazing species. The impact of their predation is worsened by the carps' size: Large adult specimens have been found to grow to 5 feet long, meaning that they need to eat more food.

The import of black carp into the U.S. has been banned ever since they were listed as an invasive or "injurious" species in 2007, under the Lacey Act.

Other invasive species in the U.S. include Burmese pythons, cane toads, gray squirrels and zebra mussels, among many others. They are considered problematic due to their impacts on native wildlife, whether by direct predation or by outcompeting other species for access to food and resources.

The fact that the black carp are now established in the Mississippi means that it will be all the more difficult to remove them from the river.

"This suggests that the environment has suitable conditions for black carp's entire life cycle," Kroboth said.

The true number of black carp occupying the 1,150,000 square miles of Mississippi river basin is unknown, but without reducing their population growth, the species may continue to reproduce and spread.

Various methods have been attempted to reduce the populations of black carp in the Mississippi basin, ranging from mechanical methods such as noise, walls of bubbles, netting and explosions, to chemical culls. The mechanical methods did not succeed at reducing the populations, only at preventing the further spread of the fish, while chemical methods like releasing the pesticide Rotenone or copper sulfate into the water proved effective at killing the invasive fish, but unfortunately also killed native fish and other wildlife.

New developments in controlling the black carp population involve the use of carp pheromones to manipulate their reproduction. Otherwise, locals are encouraged to catch and eat the carp.

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