Tough choices follow in wake of invasive species

And how do you put a price tag on the damage caused by the Burmese python and other constrictor snakes that are strangling the precious ecology of the Everglades?

Invasive species, long the cause of environmental hand-wringing, have been raising more unwelcome questions recently, as the expense of eliminating them is weighed against the mounting liability of leaving them be.

Those questions became more urgent Tuesday when a team of scientists led by the University of Notre Dame disclosed that silver carp dominating stretches of the Mississippi River and its tributaries had infiltrated Lake Michigan. The federal government had spent $22 million on electric barriers in the Chicago Sanitary and Ship Canal to keep carp out, but it clearly wasn't enough. An additional $33 million is going into the effort next year.

A coalition of six Great Lakes states and the Canadian province of Ontario sought a preliminary injunction from the Supreme Court to shut down two major locks immediately on the grounds that an Asian carp invasion would cause "irreparable harm." The court declined to grant the injunction this month, but it will accept briefs next month on the broader question of whether to close them at all.

Army Corps of Engineers officials say it's too early to shut down the locks. They are focused on building a third electrical barrier to provide yet another obstacle to Asian carp infiltrating Lake Michigan. "It's not a silver bullet, but it's a good tool to impede the movement of the silver and bighead carp," said Col. Vincent Quarles, commander of the Army Corps' Chicago District.

But the barriers are not surefire, and experts say it's difficult to say how many Asian carp would have to make it through to establish a viable population.

Southern catfish farmers began importing silver and bighead carp from China in the 1970s to eat up algae in their ponds. Some carp escaped during flooding, and now the fish so thoroughly dominate the Illinois River that communities have annual fishing tournaments targeting them.

U.S. officials have been fighting invasive species for many years, but efforts have intensified in recent years as the impact has become clear. For instance, zebra and quagga mussels that were once restricted to the Great Lakes have moved west, clogging systems at critical dams.

In the D.C. area, state and federal officials have been waging war against the snakehead, a voracious fish that infiltrated the Potomac River and occupies 70 river miles downstream from Great Falls. Scientists first detected the fish in 2004. Now thousands swim there, posing a threat to such native species as the American shad and alewife herring.

Interior Secretary Ken Salazar announced last week that he would ban the importation and interstate trade of the Burmese python and eight other large constrictor snakes that threaten the Everglades. And he recently instructed his staff to review how Interior can better combat exotic plants and animals.

"It sometimes takes dramatic evidence to bring public attention to something that's been a problem for some time," said Tom Strickland, Interior's assistant secretary for fish and wildlife and parks.