Study: Few Asian carp needed to establish foothold in Great Lakes

TRAVERSE CITY – A small number of Asian carp might be enough to establish a population in the Great Lakes that eventually could pose a serious threat to other fish species and the region’s economy, a Canadian scientist said earlier this week.

Researchers at the University of Waterloo in Ontario said in a paper published this month that under the right circumstances, as few as 10 Asian carp that find their way into one of the Great Lakes would have a 50-50 chance of becoming established. If 20 fish slip inside, the probability of gaining a foothold could jump to 75 percent, the study said.

The findings show how difficult it will be to shield the Great Lakes from the invasive fish over the long term – and the importance of developing rapid-response procedures that could limit their spread, said Kim Cuddington, an ecologist and the study leader.

It’s probably “only a matter of time before the population migrates to the Great Lakes,” Cuddington said. “We need to start thinking about how to get rid of a spawning population. Once you have large breeding populations in a couple of locations, I don’t think you’ll get them out.”

Tom Goniea, fisheries biologist with the Michigan Department of Natural Resources, said a bigger potential for carp invasion is in places such as Saginaw Bay, Thunder Bay and the western shore of Lake Erie as opposed to Lake Superior.

Asian carp, he said, thrive in high-productivity waters with agricultural runoff. That type of aquatic habitat is not common in Lake Superior.

“When you get up in the Upper Peninsula, you have standard coniferous forests without much in the way of agricutural influence,” Goniea said.

Asian carp, he said, should be expected to turn up elsewhere first.

“We would definitely anticipate seeing them in lower lakes before we see them in Lake Superior,” Goniea said.

However, Goniea said the DNR still is asking the public to be vigilant for invasive species. People can send photos to the DNR, which will identify the species.

Bighead and silver carp were imported from Asia to the southern U.S. in 1970s to control algae in fish ponds and sewage lagoons. They escaped and have infested most of the Mississippi River and many of its tributaries, including the Illinois and Wabash rivers, which could provide linkages to Lake Michigan and Lake Erie.

Authorities have spent nearly $200 million on electric barriers and other measures to block the carp’s paths.

According to the DNR website, bighead carp can reach up 100 pounds. Juveniles can consume up to 140 percent of their body weight daily while adults can eat up to 40 percent of their body weight daily. Although smaller than bigheads, silver carp can jump up to five feet out of the water when disturbed by vibrations often caused by boat motors and create a safety hazard.

Bighead and silver carp can spawn multiple times a year, thus quickly displacing native species.

Scientists differ on how many would be needed to form a growing Great Lakes population. Males and females would have to find each other in tributary rivers with fast, turbulent currents where fertilized eggs would stay afloat long enough to hatch. Cold temperatures and lack of food could hinder growth.

Because of such obstacles, some experts say it could take hundreds of carp reaching the lakes to become established. In their paper, Cuddington and her colleagues said they developed mathematical models that suggest far fewer fish might be needed.

Each of the lakes has about 10 rivers suitable for spawning – a favorable number for males and females to find one another, they said.

Duane Chapman, an Asian carp expert with the U.S. Geological Survey who wasn’t involved with the study, said its findings are based on the unproven assumption that a few carp – perhaps just one male and one female – would mate. Asian carp tend to spawn in large groups, he said.

“We know there can be hundreds of fish spawning in the same place at the same time, but we don’t know if there’s a minimum number,” Chapman said.

Another crucial factor is how quickly the carp would reach sexual maturity in the lakes, Cuddington said. If they mature and spawn by age 3, it could take 20 years to establish a moderate-sized population and twice as long for the population to become very large. But the carp could take longer to develop in cooler waters, requiring a century or more to spread widely.

Christie Bleck can be reached at 906-228-2500, ext. 250.