The Fate of the Great Lakes: Asian Carp and eDNA

The 7th Circuit, though denying five Great Lakes states injunctive relief against the U.S. Army Corps of Engineers, nevertheless acknowledged that the threatened harm by Asian carp to the Great Lakes is both imminent and extreme.[i] The states, it said, had failed to propose a solution reasonably more likely to succeed at preventing the invasion than the present electric barrier maintained by the Corps.[ii] Furthermore, since the federal government was already taking preventative measures – measures the states found, and continue to find, inadequate – it seemed inappropriate for the court to intervene.[iii] So for now, the fate of the Great Lakes resides in the hands of the U.S. Army Corps of Engineers.

But the Corps maintains a rather precarious defense, complicated by the precarious nature of the problem.  Fish, it happens, are difficult to find, difficult to catch, and difficult to direct without directing the entire body of water in which they swim.  The process of redirecting the Mississippi River, however, whether by closing locks, restricting traffic, or disconnecting it from the Chicago River entirely, would be costly, and it’s unclear who would – or should – pay for it.  Furthermore, even complete physical separation is uncertain to prevent the migration over the long term.

On the other hand, the costs of an invasion of the Great Lakes would likely be extraordinary, and almost certainly long-term:  one recent study estimates that upon entry into Lake Michigan, the carp would spread through all five lakes within 20 years.[iv] And for a species that has comprised 97% or more of the biomass in stretches of the Mississippi River basin, post-establishment management would be undeniably difficult, if not impossible.[v]

The federal government, through the Corps, has instituted a solution of questionable efficacy:  an electric barrier, standing only 30 miles from Lake Michigan.  And now the debate on the efficacy of this barrier, and therefore the actual progress of the Asian carp migration, turns on the reliability of the environmental DNA (“eDNA”) sampling technique, a test for the presence of a species analogous in procedure and rationale to modern forensics at a crime scene.[vi] But the emphasis seems untimely and inappropriate.

The eDNA technique determines the presence of specific DNA sequences in samples of water drawn from a particular environment.  Scientists define the scope of the target DNA sequence and can thereby confine it with near certainty to any particular species, since distinct species, even if closely related, have at least some distinct DNA sequences.  Polymerase chain reaction (“PCR”) amplification replicates even a single target sequence of DNA exponentially, enabling the manipulation and detection of specific sequences, and thus the DNA of specific species, in relatively short periods of time.

The controversy stems primarily from the fact that the presence of carp DNA does not necessarily imply the presence of an actual carp.  The DNA is unquestionably derived from a living or recently living carp, but the DNA’s presence beyond the Army Corps of Engineers’ electric barrier (the side nearest Lake Michigan) does not necessarily imply the presence of a carp beyond the barrier, since the DNA might have been transported by other means (in sewage and wastewater, bilge water discharge, predator excrement, etc. – but not by mere river flow, since DNA doesn’t float upstream).[vii] So rather than prompting immediate reforms in prevention management, the routine discovery of carp DNA in the waters beyond the barrier has instead provoked routine fishing expeditions by more traditional methods – poisoning, electrofishing, and netting[viii] – all in an effort to capture an living fish.  And these measures have been virtually fruitless.[ix]

The frequency of eDNA discovery beyond the barrier, however, continues to increase.  On October 9, 2012, the Army Corps of Engineers announced that 17 of 57 samples of water taken on the Chicago River contained silver carp DNA.[x] This is a dramatic increase from the Corp’s 2010 results, where only 5 of 212 samples from the Chicago River contained the DNA.[xi] More DNA suggests an increased likelihood that invasive carp lurk on the other side of the barrier.  On the other hand, it only necessarily implies an increase in the source of the DNA, which may or may not be beyond the barrier, or an increase in transportation of that DNA from its source to the waters beyond the barrier.

But eDNA is a notably more effective means of species discovery than the traditional methods.[xii] At hypothetical low population densities, for example, where eDNA discovers a species approximately ten percent of the time, the predicted discovery rate by traditional methods is virtually zero.[xiii] Though estimates, these ratios plainly suggest why eDNA might detect carp while traditional methods fail to do so.

The wisdom of the Corp’s hesitancy is diminishing, particularly in consideration of the plausibly extraordinary costs of harm should the carp successfully invade the Great Lakes, and the plausible ease with which they might presently do so.  Only a small population of carp (fewer than 10 females, and a similar number of males) is sufficient to make successful mating more likely than not.[xiv] So while it awaits confirmation by traditional means, the Corps relies on a questionably effective electric barrier to prevent a small population of an overwhelmingly invasive species from passing undetected into the Great Lakes.

Confirmation may come too late.

– Austin Anderson is a General Member of MJEAL.  He can be reached at

The views and opinions expressed in this blog are those of the authors only and do not reflect the official policy or position of the Michigan Journal of Environmental and Administrative Law or the University of Michigan.

[i] Michigan v. U.S. Army Corps of Eng’rs, 667 F.3d 765 (7th Cir. 2011) cert. denied, 132 U.S. 1635 (2012).

[ii] Id.

[iii] Id.

[iv] Canadian Science Advisory Secretariat, Binational Ecological Risk Assessment of Bigheaded Carps (Hypopthoalmichthys spp.) for the Great Lakes Basin, Canadian Science Advisory Report (July 2012), SAR-AS/2011/2011_071-eng.pdf.

[v] Dr. Michael Hansen, The Asian Carp Threat to the Great Lakes, Great Lakes Fishery Commission (Feb. 9, 2010), testimony_ aisancarp.pdf.

[vi] Dan Egan, Chicago River becomes battleground test lab, JS Online (Aug. 18, 2012),

[vii] Christopher L. Jerde et. al., ‘Sight unseen’ detection of rare aquatic species using environmental DNA, Conservation Letters, 2011, at 7.

[viii] Dan Egan, Fish barrier vs. carp DNA – what to believe?, JS Online (Aug. 25, 2012),

[ix] Id.

[x] Dan Egan, Asian carp DNA triggers new Chicago River fishing expedition, Midwest Association of Fish & Wildlife Agencies (Oct. 9, 2012),

[xi] Christopher L. Jerde et. al., supra note 2.

[xii] J.A. Darling & A.R. Mahon, From molecules to management: Adopting DNA-based methods for monitoring biological invasions in aquatic environments, Environ. Res. (2011), doi:10.1016/j.envres.2011.02.001.

[xiii] Id.

[xiv] Canadian Science Advisory Secretariat, supra note 11.