Invasive bighead and silver carp from Asia probably would not just survive but could thrive in parts of Lake Michigan, according to a new study by the U.S. Geological Survey.
The study, results of which were released this week, said there is enough of the right kinds of food in Lake Michigan for the big algae-eating fish to survive and reproduce.
The big fish are already at Lake Michigan's doorstep, moving up the Illinois River system and the Chicago sanitary waterway. They also are moving up the Mississippi and St. Croix rivers in Minnesota. They were originally imported from Asia to U.S. fish farms but escaped to populate the Mississippi River system.
The U.S.G.S. study contradicts some earlier assessments that Asian carp would need warmer, more fertile waters than are generally found in the Great Lakes.
Due to introductions of other invasive species, like alewife and quagga mussels "Lake Michigan's ecosystem has already undergone broad and rapid change in fish and other aquatic life. If bighead and silver carp were to populate Lake Michigan, they have the potential to adversely affect the ecosystem and fishing industry," the study's authors said.
USGS scientists used satellite imagery of Lake Michigan showing near-surface algae to determine how much food would be available for Asian carp. Green algae and blue-green algae, specifically floating algal blooms that can be seen on the surface, are a preferred food source for Asian carp. The water temperatures and algal concentrations detected in Lake Michigan from 2009-2011 show that the bighead and silver carp populations could not only live in this environment, but continue to grow.
The fish likely would stay close to shore and also frequent bays and river mouths, the study found.
"Most areas of the lake had insufficient algal food for bighead and silver carp, but the model indicates that nearshore areas and embayments had plenty of algal food to support survival and growth," said Karl Anderson, USGS scientist and lead author of the study.
Because the fish would concentrate near shore, that would be especially disruptive to the lake's ecosystem, with critical fish habitat for spawning and feeding usually found in those areas. It's also where silver carp, which tend to jump out of the water when spooked by motorboats, would be most likely to run into people.
The study did not look at the potential for Asian carp to thrive in Lake Superior. But earlier research suggests the big lake may be too cold for them to thrive in most areas. Russian research from 2012 shows the carp need a specific number of warm days to reach spawning potential in the lake.
The one exception would be warmer bays or estuaries, such as the Twin Ports harbor and lower St. Louis River which are warmer and more fertile than Lake Superior.
"So temperature, regardless of food availability, may have some protective capacity against colonization of Lake Superior by a reproductive population of silver carp," Duane Chapman, U.S.G.S. researcher, told the News Tribune. "This doesn't necessarily mean that Asian carp could never survive in Lake Superior - but it does mean that our best predictive abilities currently available signal substantially less threat to Lake Superior than any of the other Great Lakes."