TRAVERSE CITY, Mich. (AP) — Sport fish have declined significantly in portions of the Upper Mississippi River infested with Asian carp, adding evidence to fears about the invader’s threat to native species, according to a new study.

Analysis of nearly 20 years of population data suggests the carp are out-competing fish prized by anglers, such as yellow perch, bluegill, and black and white crappie, the report said.

Scientists have long suspected Asian carp of starving out other fish in the Mississippi and many of its tributaries. The peer-reviewed study this month in the journal Biological Invasions is among the first to establish a solid link, lead author John Chick said in an interview Friday.

“The alarms have been out there for a long time now,” said Chick, a fisheries biologist who directs a University of Illinois field station in Alton, Illinois. “This adds further mustard to the argument that we need to be taking these things seriously. The trends that have been established here are not the trends we want to see in other places.

Four varieties of Asian carp were imported in the late 1960s and early 1970s to clear algae and weeds from sewage ponds and fish farms. They escaped into the Mississippi and have migrated northward.

Bighead and silver carp are the most troublesome. They gorge on tiny animals and plants known as plankton, which virtually all fish eat as juveniles. For some filter-feeding species, itís a lifelong staple.

Federal and state agencies have spent heavily on research and technology to keep them out of key waterways.

In their paper, Chick and colleagues say there’s rarely enough data to document how invasive species harm natives.

But the U.S. Army Corps of Engineers has been monitoring fish in the Upper Mississippi system for more than two decades, including several years before the carp arrived, using electrofishing to collect samples.