They might be here or they might not be here just yet: Asian carp, the silver and bighead kind, 60 lb. monsters that can suck up 10% of their body weight in a day, stealing food from other fish.  They could fundamentally change the aquatic character of the Great Lakes.

Last spring, a single water sample taken from Lake Michigan showed detectible remnants (environmental DNA) of silver carp. Subsequent samplings turned up nothing. It may have travelled to Lake Michigan attached to a boat, or a bird, having eaten a carp may have defecated in the lake, or indeed this may have been evidence of a really bad fish now in the Great Lakes.

If it did signify a real fish, it may have come to the Great Lakes via the Chicago Area Waterways Systems, (CAWS), five waterways, 128 miles long, connecting Lake Michigan to the Mississippi River. However in a recently released white paper, the U.S. Army Corps of Engineers said emphatically, “There is no evidence that Asian carp are bypassing the [electric barriers in Chicago Sanitary and Ship Canal.] Nor is there any indication that Asian carp are in the vicinity of the barriers. The closest adult Asian carp found in the Illinois River are about 55 miles from Lake Michigan, and no small Asian carp have been observed closer than 131 miles from Lake Michigan.”

But given the findings of this same white paper, this isn’t particularly reassuring. It found that fish are being transported across the electrical barrier via “vessel-induced residual flows” created by barges. The recess area between two barges provides the dominant transport mechanism. Of the 72 samples taken, 44 included at least one school of fish passing through the barrier; and of this group of 44, 61% saw multiple fish slipping by. Research is ongoing.

(If silver and bighead carp get here, they may likely find a comfortable home. Last October Lisa Borre reported on a finding of grass carp in the Sandusky River, a Lake Erie tributary: only one-year old but with the potential to become spawning adults. Analysis revealed they were native to the river.)

The potential invasion by this really bad fish is the subject of a widely-anticipated study of what might be done to stop them. Issued on Monday by the Great Lakes and Interbasin Mississippi River Study (GLMRIS), it delineates eight options for reducing the risks posed by 13 aquatic nuisance species (ANS) including silver and bighead carp, for either the Mississippi watershed or the Great Lakes. The threat of invasives goes both ways. Which of the eight proposals is chosen is the prerogative of U.S. lawmakers; the study does not provide recommendations.

Here is a brief description of Plan 5, the Cadillac option, the most expensive at $18,389,000,000, not including annual costs.

It would address the risks posed by all thirteen ANS.  It would include nonstructural measures such as the removal of nuisance species, chemical control, controlled waterway use, inspection and cleaning of watercraft before and after entry to a water way. (These are common to all the options.) This part of the plan could be implemented immediately.

Plan 5 would provide a physical barrier between the water bodies at four locations in CAWS. To remedy the stagnant and other water quality impacts at the barriers, three of these locations would see treatment plans installed that would take Lake Michigan water, treat it and discharge it into CAWS. Water quality in Lake Michigan would see a definite uptick as sewer and storm water flows would be confined to CAWS. To address the risk of flooding two new reservoirs and conveyance tunnels would be built.

Whatever the plan and whatever the costs, a successful outcome is not assured. Prevention is regarded as the best defense, but as the GLMRIS authors make clear, “‘prevent’ means the reduction of risk to the maximum extent possible, because it may not be technologically feasible to achieve an absolute solution.”

Furthermore, aquatic pathways exist along the entire 1,500-miles between the basins, and these aren’t addressed by the engineering marvels proposed for CAWS.  And then there are the non-aquatic methods of crossing the watersheds including waterfowl migration, fishing, accidental and unregulated fish stocking.

Costs and timing pose real stumbling blocks. The cheapest option, Plan 2, wouldn’t include any water regulating structures or barriers, would only keep out five ANS not including Asian carp from reaching the Great Lakes, and would cost 68 million. From there, the Plans go all the way up to almost $18.5 billion.

Plan 5 would take 25 years to complete, that means bighead and silver carp wouldn’t be dealt with until 25 years had passed, and the clock hasn’t started ticking yet, which leaves us relying on the fine tuning of the existing electrical barriers that USACE is researching now.

Scientists take comfort in the fact that we know so much more about Asian carp than we used to. And no one doubts there is a great deal at stake. Still, we’re getting awfully close to replacing discussions of how to keep them out with how to control them once they’re with us.

The Great Lakes and Mississippi River Interbasin Study: http://glmris.anl.gov/

Summary of Fish-Barge Interaction Research and Fixed Dual Frequency Identification Sonar (DIDSON) Sampling at the Electric Dispersal Barrier in Chicago Sanitary and Ship Canal http://www.lrc.usace.army.mil/Portals/36/docs/projects/ans/docs/Fish-Barge%20Interaction%20and%20DIDSON%20at%20electric%20barriers%20-%2012202013.pdf

Asian Carps Reproducing Naturally in Great Lakes Tributary by Lisa Borre http://newswatch.nationalgeographic.com/?s=Lisa+Borre

Asian Carp face-2: photographer Kate Gardinr; Jumping Asian Carp: photographer JasonLindsey.com