TRAVERSE CITY, Michigan — Runaway growth of algae in Lake Erie since the early 2000s has made the shallowest of the Great Lakes even more vulnerable to an invasion by greedy Asian carp, federal scientists said Wednesday.
A newly released U.S. Geological Survey report said satellite imagery taken from 2002 through 2011 showed an abundance of green and blue-green algae in the lake. In some places, the amount doubled or even quadrupled during the observation period.
Algal blooms are a preferred food for bighead and silver carp, the voracious filter feeders that have gobbled huge volumes of tiny aquatic plants and animals as they've moved up the Mississippi River and many of its tributaries in recent decades.
Officials are trying to prevent them from reaching the Great Lakes, where it's feared they would destabilize food chains and out-compete existing species that support a $7 billion sport fishing industry. Lake Erie has larger populations of sport fish such as perch and walleye than the other Great Lakes.
"Remote sensing imagery shows that Lake Erie has huge areas of available food that are often several times more concentrated than necessary for Asian carp growth, particularly in the western basin," said Karl Anderson, one of the USGS researchers who produced the report.
The findings are further evidence of the harmful nature of Lake Erie's runaway algae problem, caused largely by high levels of phosphorus and other nutrients.
Phosphorus had so degraded Erie by the 1970s that some declared it dead. The problem improved significantly with laws requiring steep reductions in phosphorus content in detergents and releases from wastewater treatment plants and factories, but the algae plague returned in the late 1990s and has steadily worsened. A bloom in summer of 2011 was the largest on record, coating a 1,930-square-mile surface area with greenish slime.
An outbreak of cyanobacteria, also known as blue-green algae, prompted do-not-drink orders for two days last August that affected about 400,000 residents of northwestern Ohio and southeastern Michigan.
The USGS study found that Lake Erie's abundant algae and warm temperatures between 2008 and 2012 were enough to enable a 9-pound silver carp to gain between 19 percent and 57 percent of its body weight in a year, while an 11-pound bighead carp could gain 20 to 81 percent of its body weight during the same period.
Scientists could replicate the USGS techniques — using computer models to estimate fish appetites and satellite imagery to measure algae near the surface — for studies of how well Asian carp would do in the other Great Lakes, Anderson said. It would be a mistake to assume that the Asian carp appetite for algae would be a silver lining that might partly offset the environmental damage they would cause, he added. Some algae are known to survive even after fish eat and excrete them.
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