Created on Saturday, 09 August 2014 Written by JOHN FLESHER, AP Environmental Writer
TRAVERSE CITY, Mich. (AP) — A successful invasion of Lake Erie by Asian carp wouldn't necessarily doom its valuable sport fish such as yellow perch and walleye, a newly released scientific paper said.
The analysis concluded the nutrient-rich lake might have enough food to go around even if voracious silver and bighead carp eventually develop as big a presence there as native species. Also, the newcomers and at least some of the lake's existing fish might frequent different areas and depths, reducing competition.
But there's too much uncertainty to relax efforts to keep the carp out of Lake Erie, which has the largest fish population of all the Great Lakes despite being the shallowest and smallest by volume, scientists said.
"I would not suggest complacency," said David Lodge of the University of Notre Dame, a contributor to the paper published this week in the journal Conservation Biology. "Especially since the study didn't deal with other potential damages such as the silver carp's jumping behavior, which could negatively affect recreational boating."
Bighead and silver carp, which feed on microscopic aquatic organisms called plankton, were imported from Asia in the 1970s to cleanse sewage ponds and fish farms. They escaped into the wild and have infested the Mississippi and other major rivers. Government agencies have spent hundreds of millions of dollars on measures to shield the Great Lakes.
Scientific opinion differs on how widely the carp would spread there and their likely effect on food chains, although many warn they pose a serious risk to the lakes' $7 billion fishing industry.
"The best experiment would be to put the fish in the lake and see what happens, but we don't have that availability," said Notre Dame scientist Marion Wittmann, the article's lead author. "It wouldn't be feasible or ethical."
Instead, she and other study leaders based their findings on mathematically weighted estimates provided by 11 fish biologists and Great Lakes experts.
The paper concluded that if they gain a foothold in Erie, Asian carps' biomass — or combined weight, a standard measure of fish abundance — could exceed that of walleye and yellow perch combined.
Even so, it said yellow perch biomass wouldn't necessarily drop as a result and could even rise by up to 50 percent. The potential effects on walleye varied widely — from a 60 percent decline to a 40 percent jump.
One reason the native species' numbers might conceivably rise is that Asian carp larvae would provide them with a new and plentiful food source, Wittmann said.
Duane Chapman, an Asian carp specialist with the U.S. Geological Survey and one of the scientists consulted for the paper, said he didn't share its optimism about Asian carp peacefully coexisting with native fish. Studies of European lakes suggest baby perch and walleye might wind up seeking plankton in the same feeding grounds as adult carp, he said.
"If bighead and silver carp reach high abundance in the Great Lakes, in my opinion they'd have a substantial downward effect on ... young walleye and perch," Chapman said.