By Alex Parrish
How do you stop an army of carp from invading the Great Lakes? Two Virginia Tech researchers are joining an effort to put up a defensive barrier made of sound waves.
John Palmore, assistant professor in the Department of Mechanical Engineering, has received $340,000 from the Army Corps of Engineers’ Engineer Research and Development Center (ERDC) to create new tools using sound waves to control the movement of invasive species of Asian carp. Palmore’s group includes co-investigator and Assistant Professor Nathan Alexander in the Kevin T. Crofton Department of Aerospace and Ocean Engineering.
The center’s mission is to deliver vital engineering solutions to secure the nation, energize the U.S. economy, and reduce disaster risk. One of its principal responsibilities is managing the nation’s commercial waterway navigation infrastructure, including locks and dams.
A relatively new threat to those waterways comes from the presence of several invasive species of carp. Four species, known collectively as Asian carp, were introduced into targeted waterways in the 1970s to control harmful agents on aquatic farms. However, in the past 50 years, these large fish have moved beyond aquatic farms and now threaten the balance of aquatic life in lakes and rivers throughout the United States, gobbling up food and resources needed by other species. This threatens not only the fish that are going without, but also the fishing industries that depend on their health and wellness.
One type of carp also exhibits a somewhat alarming behavioral trait: They can leap out of the water at a distance of several feet, which can be alarming or even harmful to boaters. As the carp’s numbers increase, this jumping ability could become a widespread hazard. The invasion has extended upward through the United States, moving out of its point of origin in Mississippi and now threatening the Great Lakes in the north.
Stopping the invasion
How did the carp move so far from their original locations? While some of their early migration was the result of flooding in Mississippi, the continuing spread is mostly the work of humans.
Carp’s travel related to human activity on lakes and rivers can be both direct and indirect. When fishermen travel between two bodies of water, they often transport live bait as they go. Although adult carp are quite large, young carp may be the same size as smaller species used for fishing. As a result, transported young carp may be dumped into the water, grow to maturity, and breed in areas where they don’t belong.
Carp also take advantage of the movement of boats and water where lakes and rivers meet. Those intersections are usually controlled with dams and locks. Dams control the amount of water, and locks control the movement of boats between bodies of water.
In the case of a lock, engineers construct a small waterway – large enough to accommodate a boat – between two more substantial waterways. When a boat enters, both sides of the lock are closed. Often, one waterway is higher than the other, so the lock will either be flooded so the boat can travel “uphill,” or drained so a boat can travel “downhill.” During that water movement, nearby carp enter the lock and make a new home in the waterway.
Palmore‘s research efforts with ERDC benefit the Brandon Road Interbasin Project, a multiyear, multimillion dollar project aimed at lowering the spread of carp, specifically from the Illinois Waterway into the Great Lakes, through lock movement. Because the carp move most easily through the lock transition, the idea is to keep them away from that area.
Considerable effort has been put into stopping the spread already, particularly to safeguard the $7 billion yearly Great Lakes fishing industry. Protective measures include a combination of existing nonlethal barriers at locks and dams to deter the fish, including underwater electrical barriers, columns of bubbles, and sounds played through the water. Palmore’s team is diving into the efficacy of sound barriers when used in the locks.
“Out of all those technologies, acoustic deterrents are potentially the best in the sense that they are the most customizable,” said Palmore. “All fish are affected by bubble currents. Electric fences contain fish based on size but not species. For acoustic deterrents, each species hears within a different range. You have a selective mechanism to annoy specific species of fish.”
To keep fish at bay with sound, researchers combine different noises, such as predatorial sounds (like a dolphin), boat noises, and other irritants. The ERDC team has created the racket and tested its effect on the fish, while Palmore’s team investigates the way sound travels in water to create computational models and improved applications. The team at Virginia Tech is working with a group of ERDC’s Ph.D.-holding engineers, including Christa Woodley, David Smith, and Marcela Politano, to develop and test the tools being built.
