新托福阅读材料：8WildWaystoCombatInvasiveSpecies（7）

会计考友

　外来入侵物种对本地区的生态系统会造成许多不良影响，科学家们用自己的聪明才智研究出了许多对抗这些“外来侵略者”的有趣方法。接下来我们就一起来看看吧!  
　　Blocking Asian Carp from the Great Lakes
+ i0 Y. w! e; s
$ s* _& ~/ ?3 A. P　　They're big, they're ugly, and they're making their way inexorably north.
% o* P: R4 [7 Q
　　Asian carp—which can reach a hefty 45 kilograms—are voracious eaters. Two species—the bighead and the silver carp—are of particular concern. Catfish farmers brought these fish to the U.S. in the 1970s to clean ponds. But the carp escaped into the Mississippi River Basin during massive flooding in the 1990s. They have been migrating north ever since. The fear is that they will eventually make their way into the Great Lakes and out-compete native fish for food.
: b- J( @# @; k7 @3 j5 y
* p- l& [% T; |0 Z: k1 ]6 R　　Skittish silver carp are reviled for more than their voracious appetites. Boat motors can startle the fish, causing them to leap from the water. Occasionally they collide with a surprised boater.
, A: V; p1 e( ?. O
+ {( y9 x3 w8 R6 Y" _+ d　　In 2002 the U.S. Army Corps of Engineers erected a $4-million temporary underwater electric barrier in the Chicago Sanitary and Ship Canal, which connects the Mississippi River system with Lake Michigan. Two years later they began constructing a permanent electric barrier. A second barrier was activated in April 2009 and a third is set to be erected this fall.
! _: x4 m* w* W3 l. C! P! e
) a& ]  }% [7 Z( G　　Last November, scientists found carp DNA on the Great Lakes side of the barrier, possibly indicating that the electric fence had already been breached. Lynne Whelan, a spokesperson for the Corps, points out that the presence of carp DNA does not necessarily mean the presence of live carp. Now, however, there is even more compelling proof: In June a fisherman reeled in a nine-kilogram bighead carp in Lake Calumet, just six miles from Lake Michigan. Researchers are in the process of trying to determine whether the fish came from the wild or a fish farm, and whether he is a loner or part of a larger population.
1 }6 M7 Q5 B8 L' f* u5 E. y, |$ M
　　Twice Michigan has sued to force Illinois and the Corps to close the man-made locks that lie between the Mississippi River Basin and the Great Lakes, but the U.S. Supreme Court rejected its petitions. This latest fish find has prompted Michigan legislators to once again demand that the Corps close the locks until the two watersheds can be permanently separated. At this time, the U.S. Army Corps of Engineers says it has no plans to alter its operations.