An army of Asian carp is itching toinvade new waters again在密西西比河流域三十多年征服之后，几乎没有休息。雄心勃勃的外国鱼类仍然繁殖，即使它们耗尽原生食品供应，现在他们还涉及他们最大的奖项：大湖泊，地球最大的淡水生态系统。
Invasions are nothing new for the Great Lakes, where at least 136 exotic species already live, ranging from alewife to zebra mussels. Still, the looming attack from Asian carp — big, hungry goldfish relatives — has been stirring up widespread concern, especially since the first traces of Asian carp DNA were found in Lake Michigan last year, and the first live fish turned up past electric barriers in June. The encroaching carp have made national and international headlines, sparked a legal fight among states, and earned nearly $80 million in aid from the U.S. government.
But with the Great Lakes already under siege from a menagerie of other globe-trotting plants and animals, what's the big deal about adding a few more fish?
“伟大湖泊的条件可能允许亚洲鲤鱼超过所有本土物种，”美国鱼和野生动物发言人Ashley Spratt说。“我认为这尤其吸引了很多关注，因为它们具有多种效果 - 不仅仅是生态影响，而且是经济影响。很多人会受到影响，因为亚洲鲤鱼已经在其他地方建立了很多人可以涉及可能发生的事情。“
The Great Lakes are home to 130 endangered species, 30 million people and a $7 billion fishing industry, and Asian carp have a history of threatening livelihoods as well as wildlife. That began happening on parts of the Mississippi, Missouri and Illinois rivers in the 1990s, with many fish and commercial fishermen vanishing amid crowds of carp. An encore in the Great Lakes could be disastrous, and while there's no evidence yet that Asian carp are reproducing in Lake Michigan, that doesn't necessarily mean they aren't, points out U.S. Geological Survey fish biologist Duane Chapman.
A fish out of water
The first carp of any kind likely evolved in Asia sometime around the Late Jurassic, but humans have more recently made them one of the world's most cosmopolitan freshwater fish. After spreading across Eurasia, carp hit North America in the early 1600s as European settlers brought overgoldfish, which had been domesticated from Chinese carp 1,400 years earlier. Goldfish were soon thriving in the wild, followed in the 1800s bycommon carp。确定它们的影响并不容易，因为它们已经成立了这么长时间，但常见的鲤鱼被认为是一种害虫，因为它们踢起了可以阻挡阳光从到达藻类的沉积物云，并且由于饮食通常包括本土水禽所需的鱼卵和植物。
But the fish known specifically as "Asian carp" — which include several species, such as the notoriously jumpy silver carp pictured above — are a whole different animal. They're huge, feisty and ravenous, and many of them feast on plants and plankton that make up the base of the food chain. Each type of Asian carp fills a different ecological niche, but any of them could wreak havoc in the Great Lakes' already-embattled ecosystem. The following four species are causing the most concern:
•Grass carp:The first of the modern carp to invade America,grass carpwere brought to Arkansas and Alabama in 1963 from Taiwan and Malaysia. They're voracious plant eaters, and were imported in hopes they'd control pond weeds and other unwanted vegetation at fish farms. They did, and for years their introduction was deemed a success. But as more and more got loose and wound up in the Mississippi and Missouri rivers, they began to lose some of their luster. They can eat up to 100 percent of their body weight or more in plant matter every day — denying that food to native fish — but they only digest about half, expelling the rest as waste that can fuel algae blooms. And some may carry parasites that infect native fish, such as an Asian tapeworm they spread to the endangered伤口在80年代。
•Bighead carp:An Arkansas fish farmer first broughtbighead carpto the United States from China in 1972, intrigued by their reputation for cleaning out algae from aquaculture ponds. More bigheads were imported for research and pond-cleaning purposes over the next decade, and a few began appearing in open waters of the Mississippi and Ohio rivers by the early '80s, after either escaping from fish farms or being intentionally released. They stayed quiet for years until their populations exploded in the mid-'90s, displacing some native species like bigmouth buffalo and shad, as well as the local fishermen who relied on them. Bighead carp are now found in at least 18 states, but their appetite for algae hasn't always lived up to its billing — they are filter feeders, but they prefer zooplankton (tiny aquatic animals) to phytoplankton (tiny aquatic plants, aka algae).
•银鲤鱼：Introduced in the '70s, most likely via another Arkansas fish-farm escape,silver carp现在在全国各地的中央部队传奇，当摩托车的声音时，全国各地的半腹部发射到空中（见下文的视频）。最大的银色鲤鱼称重110 pounds, but even 20-pounders are dangerous during their forceful leaps, which can injure any people on the water. "If you're a skier, you can't ski where silver carp are abundant. That just wouldn't be smart," Chapman says. "And if you're going to be around these fish, you need to protect the boat's throttle. They can break lots of things in a boat, but if they break your throttle or knock it into gear, that's a big problem." But black eyes and boat crashes aren't the only threats from silver carp — their main food is phytoplankton, the tiny algae that larval fish and mussels need to survive.
•黑鲤鱼：Althoughblack carparen't officially established in the United States, many fishermen from the Gulf Coast to Illinois and Missouri have reported catching them more often lately. And that's just a fraction of what may be out there, says Orion Briney, who has fished Asian carp on the Mississippi and Illinois rivers for 15 years. "The black ones don't jump around, they don't show themselves," he says. "They're the ones they don't want in the Great Lakes." While their relatives gorge themselves on plants and plankton overhead, black carp stay low to hunt snails and mussels, posing a grave danger to Great Lakes mollusks that are already hurt by zebra mussels and other invaders.
Check out these videos from the Mississippi River to see silver carp in action:
The Great Lakes formed about 10,000 years ago, as glaciers slowly carved out the basins and filled them with meltwater. They've seen many ecological changes since then, but nothing like the ones brought by European settlers 400 years ago: On top of deforestation, overhunting and overfishing, they started a centuries-long habit of introducing new plants and animals to the region, often with unexpected results.
Aside from escapes and releases, many invasive species in the Great Lakes arrived in "ballast water,", which is held in large ships to make them heavier and more stable, and is also an easy hideout for aquatic stowaways. Round gobies, ruffes, zebra mussels and quagga mussels all came to the Great Lakes in ballast during the 1980s and '90s, but some of the worst invaders also entered much earlier using manmade canals. Atlanticsea lampreys在1921年，在18世纪30年代到安大略湖的途中乘坐了Welland Canal，并于1921年，迅速消灭了白鱼和鳟鱼。东白色鲈鱼在1950年代,遵循了类似的路线上decimate walleye and white bass by overeating their eggs.
As Asian carp have worked their way toward Lake Michigan, they've reached a similar network of canals that link the Great Lakes and Mississippi River basins. Built in the early 1900s, the Chicago Ship and Sanitary Canal was seen as an engineering marvel, reversing the flow of the Chicago River and allowing barge traffic to travel between the Great Lakes and the Gulf of Mexico. The canal not only sparked a booming barge business, but let Chicago send its sewage somewhere other than Lake Michigan — an important public-health move at the time, but now unnecessary thanks to modern sewage-treatment facilities.
"It's a totally unnatural connection between the Great Lakes and the Mississippi River Basin," Chapman says. "Carp have apparently exploited that, but we can't be sure; they might have been taken over by hand, too."
除了2004年德伊湖中爆发的五个孤立的小头，亚洲鲤鱼直到2009年12月，生物学家发现了密歇根湖的“环境DNA”或edna的痕迹。怀疑论者指出这些漂移的基因可能只是来自粪便或松散的鳞片，但六个月后，渔民发现了苏穆特湖的第一个活的小鲤鱼 - 超越了电障，只有六英里下游的密歇根州。根据Chapman的说法，这适合德国样本的模式，暗示亚洲鲤鱼已经在大湖中。
美国陆军工程兵团开始建设series of electric barriers along the Chicago Ship and Sanitary Canal in 2002, aimed at keeping Asian carp and other invasive species out of the Great Lakes. Steel cables now lie across the canal bottom, channeling a low-voltage, pulsing current that generates an electric field — offering a nonlethal deterrent for fish without affecting water flow or barge traffic. But now that a live Asian carp has showed up on the lake side of the electric barriers, wildlife managers are left wondering how it could have gotten there.
"The simple answer is we don't know how they would have gotten through," Spratt says. "It was specifically designed to keep them from getting into the lake, and it has been a very effective tool. Now the Army Corps is working to expedite construction of a new electronic barrier to complement the existing barriers that are there right now."
Despite the breach, Spratt says electric barriers are still a long-term solution. After all, no one really knows if Asian carp can even survive for multiple generations in the Great Lakes, and when officials used rotenone to poison a stretch of Chicago canal last year, about 90 percent of the dead fish that floated up were common carp, and just one was a bighead — although Spratt adds that other bigheads may have sunk to the bottom and gone uncounted.
Regardless, the eDNA and the live bighead have renewed calls to shut down the shipping locks altogether, which leaders in Chicago and Illinois oppose. They've drawn support from the Obama administration but the ire of other Great Lakes states — Michigan sued to close the locks last year, and although the U.S. Supreme Court declined, Michigan, Minnesota, Wisconsin, New York, Ohio and Pennsylvania are pushing ahead with another lawsuit aimed at closing them permanently. President Obama has tried to defuse the situation by giving $78.5 million to carp control — a plan that would open the locks less and use poison more — but critics argue that only closing the locks can keep the carp out.
然而，有些怀疑论者，亚洲鲤鱼无法在大湖泊中造成巨大的湖泊，因为他们是河流 - 只是看看他们在美国河流中所做的程度。但是，虽然查普曼同意他们在大湖泊的生存远离某些情况，但他说他们不应该是鸽舍。
"Bighead and silver carp are lake fish that spawn in rivers," he says. "It's a testament to their adaptability that they've been able to do as well as they have in the Mississippi. My Chinese colleagues are amazed that they can even survive here, because we don't have these big flood-plain lakes like they do in China."
Catch and relief
There's little debate that Asian carp are unwelcome in the Great Lakes, but some fishermen farther south have at least found a silver lining to the invasion. Carp can be bony and aren't widely eaten in the United States, but they do sell well overseas and in ethnic markets in New York and California, which has been enough to support small startup fisheries along the Mississippi River Basin. And Louisiana wildlife officials recently launched与厨师Philippe Parola的项目to make Asian carp a mainstream food, dubbing them "silverfin," posting recipes online and working on better methods for removing their bones.
Illinois angler Orion Briney was one of the region's first fishermen to begin successfully catching Asian carp. After watching them conquer the Mississippi and Illinois rivers where his father had taught him to fish, Briney learned to catch the famously hard-to-catch invaders and began making a living off them in the mid-'90s. For years he's been reeling in six-figure incomes by selling his catch to Schafer's Fisheries in Thomson, Ill., which distributes the meat to ethnic markets around the world. Others have joined him recently, though, which has cut into business a bit.
“今年，钓鱼的人数[亚洲鲤鱼]三倍，”布里内斯说。“这不像是这样。这笔钱消失了 - 太多人在他们之后。现在我们正在制作一半我们的东西，但这仍然足够了。”
除了钱,Briney年代ays the giant carp of a few years ago are gone, too. There are more carp now, but they're smaller, which Chapman says is happening across the Mississippi River Basin as they face the consequences of their unsustainable appetites. "You can tell the effects they have on the environment just by looking at the fish themselves," he says. "They're big and robust when they first arrive, but they get skinnier as time goes on because they're continuing to feed on that resource."
Still, the large numbers of carp mean business is "better than it's ever been," according to Briney — he used to get 18 cents a pound for black carp and 10 for silver, but now he's getting 15 for both. "Used to be, just I was out there catching them," he says. "Now there are 20 or 30 boats out there."
But many of the places already infested with Asian carp are in such dire straits, Chapman adds, that most experts now agree expanding the market is worth the risks.