Asian carp expert: Great Lakes tributaries may be more at risk than the lakes themselves

Google “Asian carp,” and you’ll return 348,000 hits. Not as many as Lindsay Lohan (21.3 million) but still plenty of choices from which to glean information on the voracious fish knocking on the door of the Great Lakes.

Michigan Environmental Council Development Associate Andrew McGlashen reverted to a favorite pre-Google tactic, personally asking an actual Asian carp expert a few questions for this edition.

Carl Ruetz is an associate professor at Grand Valley State University’s Annis Water Resources Institute in Muskegon. His research focuses broadly on fisheries biology, including an emphasis on Great Lakes invasive species. He has a Ph.D. in Fisheries from the University of Minnesota.

MEC: Recent news stories have been full of references to Asian carp, but that's really a blanket term for multiple species. Are there any differences between the species that are important to understand?

Carl: The term Asian carp refers to bighead, silver, black, and grass carps. Additionally, common carp are also from Asia but are not typically included when using the term "Asian carp." The bighead and silver carp are the two species that have caught the bulk of the recent public attention. The silver and bighead carp are filter feeders, black carp is a molluscivore, and grass carp is a herbivore. Thus, the effects that each of these carp species has on the ecosystem is quite different.

MEC: How would you characterize the response to the carp by governments, the news media, and the public? Are we all getting too freaked out? Should we be more freaked out?

Carl: The bighead and silver carp are a significant threat to the Great Lakes. Although it is highly unlikely they could colonize the actual lakes, it is possible they could colonize nearshore waters and tributaries. The tributaries probably are the most likely place that bighead and silver carp could establish. They need large river systems to reproduce.Asian Carp

Photo courtesy of Chris Olds, WSFWS -- Silver carp leap behind a speedboat driven by U.S. Fish and Wildlife Service biologist Heidi Keuler in the Illinois River near Starved Rock State Park.

However, there are many uncertainties regarding their requirements to successfully reproduce. For instance, many of the rivers that flow into Lake Michigan have dams and there are questions regarding whether there are sufficient stretches of free-flowing river for the fertilized eggs to hatch (i.e., they float downstream in the river's current). To make matters more uncertain, it also is unclear whether bighead and silver carp could use fish ladders (which are present at some of these dams) to move upstream. If bighead and silver carp were to establish in Lake Michigan tributaries, then they would likely have the biggest ecological effect on the base of the food web. Many scientists (myself included) advocate a precautionary approach that uses all feasible means to keep these fish out of the Great Lakes Basin. Additionally, the Chicago Sanitary and Shipping Canal provides an artificial connection between the Mississippi River and Great Lakes basins. This not only could provide a mechanism for bighead and silver carp to invade the Great Lakes, but also provides a conduit for future invaders. I encourage readers to look at the website of the Michigan Chapter of the American Fisheries Society. Last year, the chapter passed a resolution advocating for the separation of the two basins to prevent the spread of invasive species as well as the closure of the St. Lawrence Seaway. A good website for information on the status of bighead and silver carp is the Asian Carp Regional Coordinating Committee.

MEC: You've said we need a clear policy to prevent new invasive species from entering the Great Lakes. What might such a policy look like?

Carl: I'm not sure whether I've thought carefully enough to offer a good policy option that considers both ecological and economic realities. I think the main issue is carefully evaluating the options for separating the Great Lakes basin and Mississippi River basin. Additionally, we need to consider the multiple pathways that these fish could get into the Great Lakes (e.g., bait-bucket transfer) and implement a policy that holistically deals with the invasive species problem.

MEC: Some people say the carp are all but certain to enter Lake Michigan, but so far there's no indication that they have. Is it inevitable that Asian carp will enter the Great Lakes?

Carl: In my opinion, it is not inevitable that bighead and silver carp will become established in the Great Lakes basin. Given that it is unlikely that bighead and silver carp would thrive in Lake Michigan, I think we as a society have an opportunity to prevent them from establishing in Great Lakes tributaries. Note that an individual fish getting into Lake Michigan is very different from a population being established. Anything that is done to minimize the number of bighead and silver carp that enter Lake Michigan will reduce the likelihood that they are able to establish a population in a Great Lakes tributary.

MEC: With something like 185 invasive species in the Great Lakes already, is it even possible to make reasonable predictions about impacts? Or have we launched a huge uncontrolled biology experiment?

Carl: I am not very optimistic about our ability to predict the ecological impacts of invasive species. Ecosystems are extremely complex systems. Adding a new species into the mix can and does usually have unforeseen impacts. I do think that we can identify potential impacts. But I think it is virtually impossible to predict the true scope of such impacts on the ecosystems. I agree with your characterization that every time we add another invasive species to the Great Lakes we are essentially conducting a large, uncontrolled ecological experiment, which I think is a strong argument for taking actions to prevent invasive species from establishing in the Great Lakes. Prevention is the key.

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