Background: We all know the story of the Asian carp invasion in the US. In the 1970s, fish farmers from Southern states in the US began importing Asian carp (Silver Carp and Bighead Carp) from China in an effort to control phytoplankton blooms in their aquaculture ponds and sewage treatment lagoons. Asian carp are filter feeders; they feed on small food items at the base of the food chain. Trouble began when fish escaped into the Mississippi River watershed after floods that breached the man-made lagoons in Arkansas. Asian carp can consume up to 20% of their body weight per day. They grow quickly and can decimate plankton populations, small floating organisms that form the foundation of the aquatic food chain and are an important food source to native fishes. Asian carp outcompete native fish populations and have quickly taken over the Mississippi watershed. Once they enter an ecosystem, they are extremely difficult to eradicate; Adult Asian carp have no predators in North America and females lay about half a million eggs each time they spawn. Asian carp continue to expand their range northward, threatening the Laurentian Great Lakes.
Asian Carp in the Great Lakes? Asian carp have not yet established sustainable populations in the Great Lakes. However, there have been several close calls.
- A Bighead Carp was caught 6 miles from Lake Michigan near Chicago below the first electric barrier.
- A Silver Carp was caught by the Asian Carp Regional Coordinating Committee (ACRCC) in the Des Plaines River in Illinois only 14 kilometers south of Lake Michigan.
- Environmental DNA (eDNA) evidence has been found in several locations on the Lake Michigan side of electric barriers. However, positive eDNA doesn’t necessarily indicate presence of live carp – the source could be from a dead fish, or transported through other sources such as bilge water from boats.
- Asian carp eggs, fry and fingerlings were found in the Wabash River in Indiana. If the Wabash River floods, there is potential for Asian carp to enter the Maumee River, which flows directly into Lake Erie.
- Between 1995-2000, three Bighead Carp were found in western Lake Erie. Follow-up surveys suggest that there is not a reproducing population in Lake Erie.
There is some speculation over whether Asian carp could have a stable population in the Great Lakes. Because Asian carp are filter feeders, they need algae and plankton to sustain larger populations. They may not be able to establish stable populations in deeper, colder lakes that are less productive, such as Lake Michigan or Lake Superior. If an invasion of Asian carp in the Great Lakes occurs, it will likely take several years for the population to become problematic, based on historical carp invasions and models of invasive species, and the size of the Great Lakes.
Preventing Asian Carp entry to the Great Lakes: Prevention efforts are ongoing to keep Asian carp from entering the Great Lakes. Current actions to block invasion to the Great Lakes focus on the Mississippi River Basin (MRB) and the Ohio River Basin (ORB). The shipping canal that connects the Mississippi River to Lake Michigan is the pathway of most concern in the MRB, and multiple barriers have been established there. In the ORB, agencies like the US Army Corps of Engineers and the US Fish and Wildlife are working together to identify potential pathways for carp to enter Lake Erie where future barriers could be most effective. Physical, electrical and behavioral barriers are being used in places were Mississippi River tributaries connect to the Great Lakes.
- Physical Barriers: Dams and screens are common physical barriers to Asian carp. Dams across the Mississippi prevent Asian carp from swimming further upstream. However, most dams are not optimized to reduce carp passage. Lock and Dam #8 is the only dam on the river that has been adjusted to target carp. The Des Plaines River Bypass Barricade was built between the river and the Chicago Sanitary and Ship Canal to prevent Asian carp dispersal during a possible flooding event. Physical barriers are often used in combination with electrical and behavioral barriers.
- Electrical Barriers: Electrical barriers send low-voltage, pulsing, direct current through underwater electrodes, creating an electrified field throughout the water column. They block fish by shocking them if they get to close because a portion of electrical energy applied to the water transfers to the fish. The electric current also inhibits a fish’s ability to maintain its position in the current. When fish encounter the current, they experience galvanotaxis. Galvanotaxis is a process that immobilizes muscles and physically stops fish from moving through the barrier. It can also lead to taxis, or forced swimming. This process sometimes causes trauma or is lethal, and may requires extra infrastructure to remove dead fish. Stronger electrical currents are required to effect small fish or juveniles, which may translate to young carp passing through this type of barrier. Several electrical barriers are in use within the Chicago Sanitary and Shipping Canal to block Asian carp from entering Lake Michigan.
- Behavioral Barriers: Physical and electrical barriers are non-selective; there has been an increasing interest in barriers that use behavioral deterrents instead, such as sound, light and bubbles, because they have the potential to be species specific.
Source: Ovivo USA LLC Sound barriers were initially dismissed, but Asian Carp respond differently to sound than other fishes. The sensory mechanism in Asian carp are aggravated by complex noise, so they avoid it. Asian carp have Weberian ossicles that connect their swim bladder and inner ear. The ossicles provide carp with broad hearing and greater sensitivity than other Midwestern and Great Lakes. For example, Lake Sturgeon, Paddlefish, and Bluegill Sunfish detect sounds at much lower frequencies because they lack the connection that helps amplify sound. The use of higher frequency sound has the potential to modify carp behavior while minimizing the effect on native fish. Ambient light influences fish several aspects of fish behavior – orientation, location of food, communication between conspecifics, and avoidance of predators. Strobe lights introduce unnatural light levels that can impact fish behaviors and illicit an avoidance response. Strobe lights are not as effective in daytime or in highly turbid areas, and are suggested to be more effective when used in combination with other barriers. Bubble curtains are another type of behavioral barrier; they use a dense plume of noisy bubbles to repel fish. They also act as an unnatural visual cue for fish to avoid. Bubble curtains can be less efficient in locations with periodic high water events because they may be unable to maintain equal air pressure across differing depths. Behavioral deterrents don’t block fish 100% of the time because some fish are less sensitive or learn to ignore the barriers. Behavioral barriers are sometimes used in combination with other behavioral barriers and with physical or electrical barriers.
If Asian carp establish stable populations in the Great Lakes, it could cause declines in abundances of native fishes. Carp will compete with native fish for food and habitat. Several federally and/or state listed threatened and endangered fish rely on the Great Lakes and have been historically impacted by other Great Lakes invasives – the introduction of Asian carp could amplify those impacts and further harm these organisms.
Side Dish: The Scientific American recently published an article that encourages Americans to “carpe eat’um”. Because Asian carp are viewed negatively and are more difficult to prepare than other fish, people are not inclined to bite into a fillet o’ carp. Now, there is a movement to put Asian
carp on the menu, promoting the idea that if you can’t beat them, eat them. There is some concern over the commercializing carp. If a market develops demand for carp, people may not want to eradicate them, and may even want to spread them intentionally. However, other fish could be swapped for carp if they were eradicated, perhaps another invader could substitute for carp on the menu.
References:
National Wildlife Federation. Asian Carp Threat to the Great Lakes. Available at https://www.nwf.org/Wildlife/Threats-to-Wildlife/Invasive-Species/Asian-Carp.aspx (last accessed 21 September 2017).
Noatch MR, Suski CD (2012) Non-physical barriers to deter fish movements. Environmental Reviews 20:71–82. doi: 10.1139/a2012-001
Scientific American. Carpe Eat’um: Invasive Asian Carp Leap into Restaurants, Grocery Stores. Available at https://blogs.scientificamerican.com/guest-blog/carpe-eat-um-invasive-asian-carp-leap-into-restaurants-grocery-stores/ (last accessed 26 September 2017).
Scientific American. Great Lakes Defenders Have a Shocking Idea to Stave Off Invasive Carp. Available at https://www.scientificamerican.com/article/great-lakes-defenders-have-a-shocking-idea-to-stave-off-invasive-carp/ (last accessed 21 September 2017).
US Army Corps of Engineers. Going Green: Protecting our Great Lakes from the invasive Asian carp (2013). Available at http://www.usace.army.mil/Media/News-Archive/Story-Article-View/Article/478051/going-green-protecting-our-great-lakes-from-the-invasive-asian-carp/ (last accessed 26 September 2017).
Vetter BJ, Cupp AR, Fredricks KT, et al (2015) Acoustical deterrence of Silver Carp (Hypophthalmichthys molitrix). Biological Invasions 17:3383–3392. doi: 10.1007/s10530-015-0964-6
Zielinski DP, Sorensen PW (2015) Field test of a bubble curtain deterrent system for common carp. Fisheries Management and Ecology 22:181–184. doi: 10.1111/fme.12108