Invasive silver carp in Chain Lake

Invasive silver carp in Chain Lake
Photo: Thad Cook, Illinois Natural History Survey – a division of the Prairie Research Institute of the University of Illinois.

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Asian carp, a catch-all name for four species – bighead, silver, black and grass – were introduced to American research facilities and aquaculture ponds between 1963 and 1973. Grass carp are incredible at eating weeds that choke aquaculture ponds while bighead and silver are excellent filter feeders. They eat as they breathe, using fine combs on their gills to vacuum up suspended phyto- and zooplankton in the water. They also produce huge volumes of spawn that reach maturity quickly and can survive in just about any conditions. This makes them highly efficient pond cleaners. It also makes them a terrifying invasive.

Not long after their introduction, they escaped into the wild. Some say it happened when flood waters rose in Arkansas while others believe they were accidentally released as baitfish by unknowing recreational fishers. But their US origins matter less than what happened next. Once in the wild, silver (Hypophthalmichthys molitrix) and bighead (H. nobilis) in particular seized advantage of the opportunity to significantly expand their new-found habitat. And quickly.

Bigheads were caught in the wild by 1981. In three decades, escaped silver spread to 23 adjacent states, moving north to South Dakota and Illinois, west to Texas and east to Florida through the Mississippi and other rivers large and small, conquering new habitats and destabilizing native fisheries by outeating and outbreeding other species unfortunate enough to share a river with them. Some estimates put the total biomass in the Mississippi River – the total volume of all living plant and animal matter – at around 97 per cent Asian carp. Concentrations of silver carp are higher in the Illinois River than anywhere else in the world.

The result has been ecological destruction with mounting environmental and economic consequences on a continental scale.

Well – not quite continental. At least not yet. In early January, the Army Corps of Engineers released its 210-page Great Lakes and Mississippi River Interbasin Study (GLMRIS) report outlining eight possible short- and long-term blueprints for keeping Asian carp and other invasives from moving seamlessly between the basins. Everything from maintaining the status quo, boosting the number of electric fences and increasing the volume of pesticides released into the Chicago Canal is on the table. The most colossal proposal – to close the pathway between the Mississippi River and the Great Lakes by erecting a massive physical barrier (known as “hydrologic separation”) – comes with an asking price of US$18-billion over 25 years.

Ottawa has recently shown signs of understanding the severity of the problem on its doorstep. In 2012, Canada launched its largest Asian carp control program to date, with $17.5-million earmarked over five years towards prevention, early detection, rapid response and, though they hope it never comes to this, management of an established population. The feds are currently reviewing the GLMRIS report. Recognizing the impact hydrologically separating the two basins could have on aquatic ecosystems, marine transportation and recreational fisheries in Canada, Ottawa believes they’ll have a say in whatever final decision Washington makes.

But while the GLMRIS report and Canada’s detection efforts are pieces of a broader management strategy, they’re a far cry from what many Americans crave: a bricks and mortar fix. I was in Cleveland, I suppose, to see if we were finally talking about solutions.

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Carp-Occupied Territories

This map depicts small watersheds in the continental United States where four Asian carp species - bighead, grass, silver and black - are currently or have previously been found. While Asian carp have been known to exist in each of these watersheds, not all indicated populations are capable of reproduction. Sterile grass carp have been introduced in many areas for purposes of weed and pest control. Overlapping colours represent watersheds in which more than one species of Asian carp are present. Available data are inadequate to show the historical pattern of the species' spead, as the date of each observation does not necessarily coincide with the date of the carps' arrival in the watershed. Data provided by the United States Geological Survey (USGS).

The Invasive Four

Black Carp
Mylopharyngodon piceus
Silver Carp
Hypophthalmichthys molitrix 
Grass Carp
Ctenopharyngodon idella
Bighead Carp
Hypophthalmichthys nobilis
Average Length
60-82 cm (24-32") 60-100 cm (24-39") 60-100 cm (24-39") 60-82 cm (24-32")
Max Length
104 kg (220 lb) 45 kg (99 lb) 45 kg (99 lb) 45 kg (99 lb)
Max Weight
104 kg (220 lb) 45 kg (99 lb) 40 kg (88lb) 65 kg (143 lb)
Feeding habits
Feeds almost exclusively on molluscs, including snails. Filter feeder, mostly of phytoplankton, but also zooplankton and detritus. Primarily herbivorous, but will also eat detritus, insects and other invertebrates. Filter feeder. Often used to maintain water quality at sewage treatment plants and in aquaculture.
Interesting facts
Highly esteemed in China as one of the four famous domestic fish, they fetch a high price as a food fish. Black carp are also widely cultivated for use in Chinese medicine. They are often used as a method for controlling snails in aquaculture. Similar to bighead carp, they have no stomach. Some species of blue- green algae can pass through their gut unharmed, actually picking up nutrients while inside the fish, exacerbating algal blooms. They can also injure boaters because of their habit of leaping from the water in response to motors. Often introduced for weed control when bred as sterile triploid versions. Wary, they can be hard to catch, but are popular bow-hunting targets. They will eat canned corn and cherry tomatoes, often used as chum to attract the fish for sport fishing. Similar to silver carp, they have no stomach and feed constantly. Banned in Canada for sale or importation. Often they are still sold illegally as a food fish. Bighead are also a popular target for bowfishers.
Introduction date
1972 Considered a "contaminant" in imported grass carp stock. They were imported for use in pest control in aquaculture. Released to the wild for the first time in Missouri in 1994 when floodwaters overcame aquaculture ponds near the Lake of the Ozarks. 1973 Initially privately imported in Arkansas, they were first found in natural waters in 1980, likely as the result of accidental release from several facilities. Introduction in Florida likely occurred as contamination of an intentional grass carp release for aquatic plant control. 1963 First imported from Taiwan and Malaysia for use in aquaculture in Alabama and Arkansas. In 1966, they were accidentally released from a US Fish & Wildlife Service fish farming experimental station in Arkansas. 1972 Imported to Arkansas, they were discovered in open waters in the early 1980s, likely as the result of escapes from aquaculture facilities. They were also released in the same flooding event in 1994 that released the black carp into the wild near the Lake of the Ozarks.

Andrew Reeves is an environmental writer completing a book about Asian carp in North America. He is a contributing editor at Alternatives Journal and This Magazine’s environmental columnist. His work has also appeared in the Globe & MailSpacing and Corporate Knights.

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