Scientists measure extent of Asian carp invasion in US rivers

(13 Jul 2012) STORYLINE:
River ecologists in the US have taken to their boats to attempt to settle the debate about the impact of Asian carp.
Some scientists have predicted that the fish - an invasive species introduced 30 years ago to control plankton and algae in Arkansas fish farms and sewage lagoons - could decimate native fish stocks in the Great Lakes.
Others contend that the Lakes waters would be too cold and anyway food supplies could support both populations.
But research shows that the carp which escaped into the Mississippi river system when fish farms were flooded, now make up more than 60 percent of the combined weight of all fish species in some stretches of river.
And they're eating their way northwards, consuming up to one-fifth of their body weight in a day.
Already they're established in more than two dozen states, as far as Kansas and the Dakotas, and within 55 miles (88 kilometres) of Lake Michigan.
What's missing, though, is clear evidence that Asian carp will devastate other fish. Even in places such as the Illinois and Mississippi, where carp are rampant, changes have been incremental.
Many experts say if the hardy fish establish a foothold in the Great Lakes, they're likely to find hospitable conditions in bays, nearshore areas and tributary rivers. Warm, shallow Lake Erie, with the most abundant fish numbers, is an especially ripe target.
"They are knocking on the door of the Great Lakes, through the Chicago Sanitary Shipping Canal," said Levi Solomon, ecologist at Havana Biological Station, Illinois.
The main prevention measure is an electric barrier on the Upper Illinois river that prevents fish from moving through but several states are demanding more substantial measures from the federal government, with court action pending.
While years of study have turned up ominous signs that the carp are capable of crowding out other species and changing ecosystems, the worst-case scenario which some scientists predict has not yet happened.
Research so far has focused on rivers, where Asian carp are most plentiful, counting the fish stunned by an electric current, which can cause a spectacular display of jumping fish.
Big money is at stake. The fish could supplant river species widely harvested for food. And the Great Lakes leisure angling industry is said to be worth seven billion US dollars a year.
Government agencies have already spent more than 150 (m) million dollars on technology to repel the invaders and five states are suing the federal government to blockade the Chicago Ship canal, which would take years and cost (b) billions.
A US-Canadian team is expected soon to release a Great Lakes risk analysis following an 18-month study.
Calculating damage from Asian carp is slow and often frustrating work, thanks in part to the ever-changing nature of rivers.
Fluctuating water levels, nutrient runoff and temperatures also affect fish numbers.
Some scientists say that predictions about the damage carp can do may be premature, which makes the current research critical.
It likely will influence how the debate over managing waterways said to be at risk is played out in Congress and the courts.
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