Asian carp could be a lot worse to the Great Lakes than previously thought, UofM study shows

Image 1 of 3

Scientists thought Asian carp’s threat to the Great Lakes would be limited.

They may have been wrong.

A new study released by the Cooperative Institute for Great Lakes Research (CIGLR) found the potential threat posed by two types of the invasive species could be much larger if Asian carp invade the Great Lakes.

“In terms of impact, based on our models that say what they can do, they are capable of significant detrimental impacts,” said Peter Alsip, lead author of the study, 

The specific fish in question are bighead and silver carp - the two subspecies of Asian carp that eat plankton and zoo plankton, which are two key sources of food in the lower tier of the lake’s food web. Previous studies warned if either established themselves in Lake Michigan, not only would they out-compete the fish that also eat plankton, but they could decimate the plankton population as well.

But what about all the dead organisms and biomass (fish poop, decomposing organisms) that lies on the lake bed? Both bighead and silver carp are known to feed on this “detritus”. When scientists estimated Asian carp's threat to the Great Lakes, they didn't factor in this separate source of food. 

Alsip’s study however did consider this detail, and he found that not only could it make it easier for Asian carp to establish themselves in Lake Michigan, it could also make it easier for the species to spread around the lake and to its tributaries.

“They primarily eat plankton, but they are really opportunistic feeders,” Alsip said. “When their preferred food isn’t available, they’ll switch to others.”

Much of the “others” that Alsip is referring to is the excrement left by quagga and zebra mussels - another invasive species that’s wreaked its own brand of havoc on the Great Lakes. Dubbed “fecal pellets,” these little pieces of poop can be found wherever quagga and zebra mussels are, which is everywhere.

This lethal combination of ‘flexible diet’ and diverse selection of food makes Asian carp’s threat to the Great Lakes a dangerous one.

Asian carp’s introduction to the U.S. is one of the country’s better documented invasions from a foreign fish, and equally tragic considering it was brought here intentionally. Imported in southern U.S. in the 1970s as a means to control algae blooms, they quickly established themselves in the Mississippi River. From there, several of the species made their way north.

Populated throughout the Midwest, their numbers have been spotted in the Illinois River, an out-flowing river for Lake Michigan. Electric and bubble barriers have been put in place to keep the fish out, however officials still worry the species could breach the Great Lakes.

Are the Great Lakes next? Video shows hundreds of Asian carp shocked in Kentucky lake
Great Lakes Conservation Coalition formed to stop Asian Carp

When assessing the threat level faced by silver and bighead carp in the Great Lakes, researchers relied on satellite data and water samples of viable habitats for both bighead and silver carp. However, both kinds of data had their limitations and didn’t take into account what Alsip has now considered.

“Those studies were very foundational and like any other science, we’re advancing the dialogue of what they (researchers) have done,” Alsip said. “What we wanted to say, ‘now that we have the ability to look beneath the surface and consider new prey options, let’s build on our current knowledge.’”

Most of the viable habitat for Asian carp were nearshore locations - the same places where much of the plankton and zooplankton are. However, due to declining levels of phosphorus in Lake Michigan, the amount of available food has been reduced. 

This decline led some scientists to be skeptical of bighead and silver carp’s potential for establishing itself in the lake. But a lack of plankton won’t limit Asian carp’s advances if they have another food source to feed upon.

Alsip said he wouldn’t expect carp to wander away from more productive parts of the lake. But given a good enough reason to migrate elsewhere, the option of another food source could enable them.

“They could potentially survive a journey through less-productive areas as they seek out other feeding grounds,” he said. “And these fish have been shown to seek out higher prey densities if they have the motivation to travel across the lake.”

For officials working to keep the carp from intruding in the Great Lakes, the study's results further validated the need to protect them. The vice president of policy at the Alliance for the Great Lakes released this statement:

 “The University of Michigan led study confirms what we’ve long feared: invasive Asian Carp could not only survive but thrive in Lake Michigan and its tributaries," said Molly Flanagan. "We are on the verge of an unstoppable crisis for the Great Lakes region, and now is our best chance to stop these aggressive fish from crashing our economy and environment."

One of those solutions includes erecting barriers in the Illinois River. However, the project recommended by the U.S. Army Corps of Engineers, a fortification of the Brandon Road Lock and Dam, carries a hefty price tage, and remains a sticking point among those skeptical.

Alsip’s study was part of his Master’s thesis at the University of Michigan. His study was co-authored by his adviser Hongyan Zhang of the Eureka Aquatic Research, as well as researchers from NOAA’s Great Lakes Research Lab, the Michigan Sea Grant and the Department of Natural Resources.