How serious is Asian carp threat to Great Lakes?

Some fear that if invasive Asian carp enter the Great Lakes, the multi-billion dollar recreational fishing and tourism industry there will be devastated.

The first week of August, 2011 was not a good week to be a fish in Chicago’s Lake Calumet. The Asian Carp Regional Coordinating Committee (ACRCC) unleashed over 1,000 person-hours of electroshocking, fishing, and netting in an effort to find Asian carp in the lake. In spite of all this manpower, the four days of intensive fishing, netting and electroshocking caught 8,668 fish but not a single one of an Asian carp species.

Does that mean Asian carp – which have transformed rivers in Illinois and other states – are not a threat to Lake Calumet and to the Great Lakes generally? Predicting the magnitude of the Asian carp impact upon the Great Lakes is no easy task. Scientists disagree about how seriously to take the threat.

No other fish in the U.S. Midwest excites as much media attention as Asian carp. Since escaping from aquaculture farms in the 1970’s, these fish, primarily bighead and silver carp, have traveled up the Mississippi river basin and now hover around Chicago just outside the Great Lakes.

Today, in some sections of the rivers in Illinois and other states, people estimate that carp are up to 95 percent of the biomass.

Unlike their fellow invader bighead carp, silver carp are especially notorious for jumping out of the water when scared and have become a scourge on Illinois rivers (see video above). Residents of the Great Lakes area are fearful that if these fish enter the Great Lakes basin, the multi-billion dollar recreational fishing and tourism industry will be devastated.

Image Credit: U.S. Fish and Wildlife Service

News of these fish broke into the national media in 2009 when environmental DNA (eDNA) of silver carp was discovered above electric barriers in Chicago. All organisms lose DNA to the environment. Humans lose it from fallen hair, dead skin, etc. The eDNA method detects if any lost DNA from an organism is present at a site. If so, then you can hypothesize that the organism might have been near this location. However, you cannot be sure.

The uncertainty exists because finding eDNA does not guarantee a live fish exists above the barrier. DNA from carp could come from bilge water or other mechanisms. According to monitoring protocols, when three consecutive positive eDNA results of Asian carp are found, an intensive monitoring event occurs to try to catch an actual fish. The intensive monitoring at Calumet Lake the first week in August was a result of eDNA samples with silver carp DNA found in June and July 2011.

Image Credit: U.S. Army Corps of Engineers

Electric barriers erected by the Army Corps of Engineers are designed to prevent Asian carp from getting too close to the Great Lakes. The barriers emit an uncomfortable electric field into the water, repelling fish from swimming upstream. Electric barriers prevent fish from entering the Great Lakes but still allow shipping to continue through canals and rivers. The other prevention option to ensure fish do not enter the Great Lakes entails closing off the shipping canals completely. However, this would result in large economic losses as transporting goods between the Great Lakes and Mississippi would become more expensive.

The presence of eDNA above the barriers has caused some to question their effectiveness. For example, a recent article (PDF) by Jerry Rasmussen in the Journal of Great Lakes Research calls for the complete separation of the Mississippi and Great Lakes watersheds by closing the shipping canals of Chicago.

The status and presence of Asian carp in the Chicago region still contains great uncertainty. Monitoring of eDNA sometimes detects the presence of carp DNA, but no actual fish are found.

Moreover, the percentage of eDNA samples that indicate a positive carp DNA match is very low. Of the 941 silver carp samples taken from May-August 2011, only 14 resulted in a positive eDNA match.

Illinois rivers have been transformed by the carp species, but the Great Lakes ecosystem can be quite distinct from rivers further south. Therefore, predicting the magnitude and extent of the Asian carp impact upon the Great Lakes is no easy task and scientists are in disagreement about how seriously to take the threat. The Jerry Rasmussen article mentioned above responds to other scientists’ beliefs that the carp impacts on the Great Lakes will be minimal. Furthermore, the issue might begin to gain more national attention again, since the attorneys general from six Great Lakes states recently announced they will be contacting 27 other states in an effort to gain more support for ramped-up efforts to ensure that carp cannot enter the Great Lakes.

In the end, speculation about how imminent an entry into the Great Lakes is shall rule the day until an actual live Asian carp can be caught above the electric barriers.

Bottom line: Since escaping from aquaculture farms in the 1970’s, Asian carp have traveled up the Mississippi river basin. Today, in some sections of the rivers in Illinois and other states, carp may be up to 95 percent of the biomass. Now, this invasive species is thought to hover around Chicago just outside the Great Lakes. But scientists disagree about how seriously to take the threat, and predicting the magnitude of the Asian carp impact upon the Great Lakes is no easy task.

Keith Hayse-Gregson & James Diana

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