The Great Lakes may be under threat from an Asian invader.
Grass carp, a kind of Asian carp, are capable of naturally reproducing in the Great Lakes watershed, according to a new U.S. Geological Survey study. The discovery comes after four grass carp were pulled from the Sandusky River in Ohio and biologists confirmed they had lived in the basin their entire lives. The results show the invasive species, that came to the U.S. from Asia decades ago, may threaten native fish, duck and geese populations in the Great Lakes.
"These findings are significant because they confirm recent USGS research indicating that shorter rivers, like the Sandusky, are potential spawning sites for grass carp and other Asian carps as well," USGS scientist Duane Chapman said in a news release. "The study may also provide resource managers an opportunity to address the spread of grass carp before it becomes problematic."
While fish experts have previously thought carp needed longer rivers without dams to reproduce, the latest results show that some species of carp can spawn in bodies of river as short as 15 miles, the Milwaukee Journal-Sentinel reports. Dams were believed to act as a barrier for Asian carp that need free-flowing water to keep their eggs floating before they hatch. But the latest study findings show the dams don’t hamper spawning entirely.
"This is very important because it means Asian carps have many more potential spawning locations in the Great Lakes than we thought possible," Chapman said.
The latest study, published in the Journal of Great Lakes Research, involved analyzing the chemistry of otoliths, fish ear bones, to see where they lived over their lifetime. Multiple results including a high ratio of strontium to calcium in the Sandusky River and comparably high numbers in the otoliths, suggested the carp were a result of natural reproduction.
“[It] indicates that these fish lived in a high-strontium environment throughout their entire lives,” the study authors write.
While experts are typically more concerned with preventing the growth of bighead and silver carp populations in the Great Lakes, Chapman warns the grass carp have similar spawning requirements and may be an equal threat in the region and elsewhere, the Associated Press reports.
"It also means many more reservoirs in the United States are at risk of Asian carp establishment," he said.