On July 17, the Detroit Free Press ran a six-part series on the Asian carp threat to the Great Lakes. This is an issue that I’ve been following for some time, after I had interviewed University of Michigan fish biologist, Gerald Smith, on the Drunken Skeptics podcast.
The concern is regarding whether if Asian carp (specifically, the bighead and silver carp) enter the Great Lakes, will they have a detrimental impact on the ecosystem? And from there, the specific assertions state that the invasive species will adversely affect the fishing industry, tourism and sporting industry, and take over Michigan river systems.
Currently, there is an electric barrier in the Chicago Sanitary and Ship Canal that’s designed to prevent the fish from passing through it. And researchers are monitoring the waterway for evidence of Asian Carp getting past the barrier. There is also a law against the transportation of the fish across state lines.
This issue has garnered much attention, but it may be surprising for some to find that this issue is very controversial within the scientific community. Fish biologists from the University of Michigan, like Gerald Smith, are skeptical about whether the Asian carp can survive and flourish in the Great Lakes. Smith is quoted in the Freep story.
“Ninety-nine percent of the Great Lakes are too cold for these fish to succeed,” he said.
In my interview with Smith last Fall, he provided an overview of the issue and why he became skeptical of the Asian carp threat and media attention. Here’s an audio excerpt:(Asian_Overview)
Smith explained that all of the fish biologists at the University of Michigan disagree with the assessment that Asian carp can take over the Great Lakes. (Asian_ScientificConsensus)
And so they developed their own risk analysis. (Asian_RiskAnalysis)
Aside from the water temperature point, Smith and the other biologists argue that another factor that would prevent Asian carp from succeeding in the Great Lakes ecosystems, is that the eggs and young would succumb to predation. Asian carp minnows is a popular bait for sport fishing. So an emergence of Asian carp could actually boost fish stock which have been declining. (Asian_Predation)
EVALUATING THE EVIDENCE
So how should skeptic-minded folks consider this topic?
Well, the scientific arguments offered by the skeptics of the Asian carp threat are as follows:
1) Asian carp (like its established cousins, the common carp) can only survive in warmer waters (about 1% of the total Great Lakes). The commercial fishing industry won’t be affected by the Asian carp because it utilizes the deeper, colder waters. Several studies that suggest Asian carp would be acclimated to the Great Lakes utilize air temperatures, not water temperatures. And several independent researchers have used average lake temperatures, but don’t take into account the winter temperatures.
2) The diet of Asian carp is phytoplankton. And phytoplankton levels are already very low because it is also the diet of zebra and quagga mussels – which are an established invasive species that are succeeding (unfortunately, all too well). And therefore, Asian carp will be out-competed.
3) In the warm, shallow areas in which Asian carp could live, they would experience heavy predation by other fish stock as they would find eggs and young as a source of food. And this fish stock could get a much-needed boost.
4) If Asian carp get into rivers, they would need long stretches of water that have no dams – for spawning. However, most rivers in Michigan have dams which would make reproductive success very challenging.
It’s important to note that these four points are not agreed upon by all fish biologists. As the Freep story reports, some fish biologists at other institutions expect the Asian carp to adapt to the Great Lakes ecosystems (although it would take many decades for this to happen). And once this happens, it will be too late to do anything. The Michigan Sea Grant is one such organization that believes the Asian carp are a threat.
Bill Taylor, a professor in global fisheries sustainability at Michigan State University also is concerned by the Asian Carp threat. He believes that the Asian carp will dominate the shallow, warm waters of the shores and make their way into the rivers.
“The Asian carp are going to whack the tributaries,” Taylor said. “They’re going to eat all the food – they eat anything they get in their mouth and that means they’ll eat the food base that our resident fish would normally eat. They will change the food web and dominate our streams and near shore regions in the Great Lakes basin.” [MSU News]
News reports of Asian carp DNA being found past the electric barrier (although not any live specimans) have emerged in the past year. This shouldn’t be surprising, since it would be reasonable to expect that Asian Carp waste material or decomposing bits could pass through the barrier. But some researchers are convinced that Asian carp are beyond the electrified field.
“We’re assuming (the fish) are there because we have to,” said John Rogner, assistant director of the Illinois Department of Natural Resources. “It’s the best data we have.” [Milwaukee Sentinel]
However, despite the skepticism towards this issue, it’s important to keep in mind that invasive species, in general, are a threat to any ecosystem. Invasive species disrupt the food chain due to the fact that they consume and reproduce with little risk of predation. And all fish biologists would like to see policy changes that minimize new organisms from getting into the lakes.
The quagga and zebra mussels are one such example. Because they face no predation, they have out-competed other native species that feed on phytoplankton (although quagga mussels with their softer shells have been found in the stomachs of some predators, such as whitefish and some perch).
Yet, biologists like Smith, do not want science to be manipulated by politicians either. Many people would love to see the Great Lakes separated from the Mississippi river basin for political and economic reasons. And it’s believed by many (such as Smith) that the Asian carp issue is being used to that end.
Ultimately, I’ve come to accept that the robustness of the political force driving this issue exceeds the robustness of science behind it. Personally, I’m more concerned with pollution from industry and agricultural run-off affecting the Great Lakes ecosystem. But I strongly believe in further studies and research, as well as continued monitoring.
The Army Corp of Engineers has begun a long-term study, called the “Great Lakes Mississippi River Interbasin Study” that will be completed in 2015. And there are several research teams generating their own studies, as well as developing solutions to warding off the Asian carp from the Great Lakes waterways.
I e-mailed Smith about whether his position has changed at all since last Fall, in particular as to whether Asian carp could be a threat to the shallow waters and river systems.
He replied, “I am still a skeptic.”