Thursday, March 09, 2006

Keeping Bighead and Silver Carp Out of the Great Lakes

Listen to the commentary
Real Audio : MP3 download

[Click this link to see Illinois Natural History Survey video of silver carp leaping out of the water in response to boats.]

You know that old story of the Dutch boy who stuck his finger in the dike to prevent a flood? Well, his task was easy compared to the task facing researchers from Illinois and neighboring states who are trying to prevent an invasion of the Great Lakes by two species of carp native to Asia, the bighead and silver carp.

This story dates back to the 1970s, when bighead and silver carp were imported to the southern United States from China in order to control aquatic vegetation and plankton blooms in fish-rearing ponds. Whether they then escaped during floods or were released intentionally, they began showing up in the Mississippi River Basin by the early 1980s.

Since then, bighead and silver carp have made their way steadily north, up through the Illinois River system toward the Chicago Sanitary and Ship Canal. Created in the late 1800s to divert sewage from Chicago, the twenty-eight mile long canal provides the only direct aquatic link between the Mississippi River and Great Lakes basins. Blocking passage of the carp through the canal is a crucial element of the fight to keep them out of the Great Lakes.

The first defense against the movement of bighead and silver carp into Lake Michigan has been an experimental electric barrier, which was constructed near Romeoville, and began operation in Spring of 2002. This barrier uses electrodes deployed in a cross-section of the canal to create a wall of electric current. The electricity irritates fish as they approach and causes them to turn around.

A new, more permanent barrier using two electric arrays is in the final stages of installation, and should be fully operational this summer.

Working with funding from Illinois-Indiana Sea Grant, researchers have also been investigating the potential for using an acoustic barrier to prevent the movement of fish through the Chicago Canal. The system they have developed uses sound projectors that emit chirping noises which repel fish, combined with an air line that generates a wall of bubbles. The bubble-wall amplifies the projected sound and causes additional disturbance to fish.

The design for the acoustic barrier is relatively simple, which means it might be an affordable way to augment the electric barrier. In addition, since it requires little electricity it could be run with a generator during a power outage.

Of course effective barriers can only stop fish from swimming into the Great Lakes on their own. It is equally important that people, especially anglers and boaters, not move invasive species from one body of water to another. This is a great concern with bighead and silver carp, since the young of both species closely resemble gizzard shad, a native North American fish commonly caught for use as bait. If you fish or boat I would encourage you to check out the educational materials Illinois-Indiana Sea Grant puts out on invasive species, to help ensure you don’t inadvertently contribute to the problem. [Scroll down to the "Featured Products" section at this Illinois-Indiana Sea Grant link.]

Researchers are still assessing the impact of bighead and silver carp on ecosystems and fisheries in the Mississippi River drainage, and it is hoped that the high productivity of that system will blunt the damage they cause there. There is little hope that Lake Michigan would fare so well, since it is a less productive system to begin with, and it has already been hit hard by zebra mussels and other invaders. By committing resources to stop the spread of bighead and silver carp now, we can prevent one nightmare from becoming a reality for the Great Lakes.

A special thanks to Irene Miles and Pat Charlebois of Illinois-Indiana Sea Grant, and Phil Moy of Wisconsin Sea Grant for help with this program.