The bait fish business and the anglers who make use of it present a serious risk of introducing invasive species of fish into the Great Lakes area, a study suggests.

Water samples taken from tanks of bait fish on sale at 500 shops in the states surrounding the lakes found 27 that tested positive for DNA of invasive species such as Asian carp, researchers said.

The study by Central Michigan University and the University of Notre Dame suggests anglers may be spreading some of those invaders by dumping unused bait in the lakes.

"While overall only a small percentage of bait shops had evidence of invasive species, it is nevertheless alarming that at least some invaders are being spread by anglers, the very group of people that value the Great Lakes fishery the most," said CMU researcher Andrew Mahon, one of the paper's co-authors.

The researchers describe their research as a first effort to reveal the existence of invasive species by testing bait supplies for "environmental DNA," evidence of genetic fingerprints of particular fish.

Analyzing the water in which bait is sold is more effective than just examining the bait fish themselves, the researchers say, since a usual bait tank may contain thousands of small fish such as minnows, and invasive fish can often be difficult to tell from native species at that early stage of life.

Analyzing water samples for DNA can yield a better picture of the types of species present than can be garnered from few samples of fish taken out of a tank for a visual inspection, they say.

While many states around the Great Lakes actively urge anglers to not dump their unused bait supplies into the water, not everyone follows the recommendations, the researcher said, citing a study in Canada which found more than 30 percent of anglers were releasing unused minnows into area waterways rather than disposing of them in recommended ways.

While most efforts to keep invasive species like Asian carp out of the Great Lakes involve physically blocking likeliest entry points, bait fish must be considered as a significant threat, the researchers say.

"If we ignore this pathway for spread of invasives, then we will likely be too late to prevent the damages they could ultimately cause," Central Michigan biologist Lucas Nathan, the study's lead author, says.

Invasive species in the Great Lakes are considered a serious threat to disrupt the aquatic food chain by outcompeting native species for available food supplies.