Evidence of Asian carp spawning has been discovered as far north in the Mississippi River as Pool 9, which borders Iowa’s Allamakee County.
"This discovery means that Asian carp spawned much farther north in the Mississippi than previously recorded," said Leon Carl, Midwest regional director for the U.S. Geological Survey.
The eggs and late-stage embryos-- collected last May and June and recently identified -- were 250 river miles upstream of previously known reproductive populations in the river.
Carl said the invasive Asian carp could pose substantial environmental risks and economic impacts to the Upper Mississippi River if they become established.
Both silver and bighead carp are filter feeders that compete with young fish for food. The silver carp, which often leap from the water, present an additional threat to boaters.
"The presence of eggs in the samples indicates that spawning occurred, but we do not know if eggs hatched and survived or whether future spawning events would result in live fish,” Carl said.
Iowa Department of Natural Resources fisheries technician Kevin Hanson, stationed at Guttenberg, said the news was not a big surprise.
Commercial fishermen in waters above and below Guttenberg had netted a few Asian carp in the past two years, he said.
In pool 13 near Bellevue, commercial fisherman have netted about 6,000 pounds of Asian carp in recent years, Hanson said.
But it remains to be seen whether the invasive species have established a reproducing population in pools 9, 10 and 11, he said.
Once the scientists visually identified the eggs, they examined other samples taken from the Mississippi River and found Asian carp eggs at seven locations between Pool 19 near Keokuk, Iowa, and Pool 9 of the main channel of the Upper Mississippi River near Lynxville, Wis.
The eggs and late-stage embryos were identified as either bighead carp or silver carp through visual analyses of specific features of the eggs and embryos.
Results of genetic analyses to definitively determine which species of Asian carp the eggs belong to were inconclusive. Results of additional genetic analysis are expected in one to two weeks.
Scientists plan to collect additional samples from the Mississippi this year as part of their on-going research project.Asian carp have been found in many Iowa rivers including the Cedar and Iowa, as well as in the Iowa Great Lakes.