Lamprey Love Potion

Sea lampreys earned the alias "vampire fish": After all, they suck blood. These long, parasites are similar to eels and use their suckerlike mouths to latch on to the bodies of other fish. Then they rasp a hole in the fish's skin with their tough tongues. In the Atlantic Ocean, the lamprey's home, this isn't such a problem: The fish are big, and they can spare some blood. But in the Great Lakes, where lampreys arrived a century ago, the fish are smaller, and a lamprey bite can be deadly. "Many fish that get attacked by the sea lamprey eventually die," says Weiming Li, a fisheries professor of at Michigan State University. In fact, these slimy suckers were at least partly to blame for the collapse of lake trout, whitefish and chub populations in 1940s and 1950s.

Lampreys, which breed in freshwater streams and tributaries, find their mates by scent. In 2002 Li and his colleagues identified a pheromone that male lampreys use to attract their mates. Perhaps, they thought, we can use the chemical to lure lampreys into particular streams to make trapping easier. So the researchers created a synthetic lamprey love potion.

Over the past few years, they tested it out in a few "pristine" streams, places where lampreys don't already breed. Li and his colleagues found that just a small amount is enough to lure females into these waterways. This year they started testing the compound in streams where lampreys already breed. So far, the results look promising, Li says.

Using pheromones to lure females into areas where they can be easily trapped is the most straightforward application, Li says, but the synthetic chemical could be used in other ways, too. He envisions employing it to coax female lampreys into areas where their larvae are less likely to survive.

Snuffing out Smelt in Northern Wisconsin

This giant disk of black rubber may seem harmless, but don't be fooled. This gizmo—called a GELI, short for Gradual Entrainment Lake Inverter—is designed to kill. It's the newest weapon in the war against invasive rainbow smelt, a native of the North Atlantic states.

Rainbow smelt were brought to the Midwest in 1912 as food for fish farm salmon. But the tiny fish soon escaped into Lake Michigan and then moved into Wisconsin's inland lakes, perhaps by hitchhiking in fishermen's bait buckets. In Wisconsin alone smelt have already invaded about 25 lakes, "and every year they tend to pop up in another lake," says Jake Vander Zanden, a biologist at the University of Wisconsin–Madison's (U.W.) Center for Limnology. Smelt compete with other species for food and feed on baby fish, including trout, walleye, yellow perch and cisco.

How will the GELI help to get rid of smelt? The goal, says Jordan Read, an environmental engineering graduate student at U.W.–Madison, is to "flip the lake on its head." Temperate lakes tend to stratify, with cold water sinking to the bottom and warm water floating on top. Smelt like the cold water. If the cold water disappears, so will the smelt—or at least that's the hope.

The researchers plan to test this idea out in Crystal Lake, an 84-acre lake in northern Wisconsin. In 2011 they will put about a dozen of these devices in the middle of the lake. Each disc has an inflatable tube running around the rim that is connected to an air compressor. Once the device has sunk to the bottom of the lake, the researchers can start the compressor, fill the tube, and the GELI will rise slowly to the surface, bringing up a large volume of cold water from the lake bottom. Once the GELI hits the surface, the tube will deflate and the GELI will sink again, bringing warm surface water to the bottom. "Eventually we erode that stratification," Read says.

The baby smelt don't mind warm water, so to wipe out the entire smelt population the researchers will have to mix the lake for several years. According to Vander Zanden and Read, the mixing shouldn't have an impact on native fish, which can tolerate warmer waters. The hope is that once the smelt are gone, native fish like yellow perch will rebound. "One of the big ideas here," Vander Zanden says, "is to test of whether the ecosystem can really be brought back to something resembling its original state after eliminating this nasty invasive."

Blocking Asian Carp from the Great Lakes

They're big, they're ugly, and they're making their way inexorably north.

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.

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.

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.

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.

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.

Combating Cane Toads in Australia

In the 1930s farmers released thousands of poisonous cane toads native to Central and South America into sugar plantations around Cairns, Australia, in the hope that they would rid the fields of beetles. Big mistake. The plan failed, and the toad spread across northeastern Australia, gobbling up native insects and poisoning predators that mistakenly fed on them.

Rick Shine, an evolutionary biologist at the University of Sydney, has been studying the ecology of the invasive cane toad since 2004. "We kept finding all these vulnerabilities," Shine says. For example, the frogs that are native to Australia know how to avoid large, carnivorous ants because they've evolved with them for millions of years. The toads, on the other hand, "have all the wrong responses," Shine says. The baby toads come out of their ponds when the ants are most active. And, when they encounter an ant, rather than hopping away, they freeze.

The researchers found that they could attract meat-eating ants to the ponds where cane toads breed by setting out cat food. When the toads emerge, the slaughter begins: The ants attacked 98 percent of the toads in the first two minutes. Of those, 70 percent died. "Their poison doesn't affect the ants, so they just get creamed in huge numbers."

Shine's lab is also looking at ways to train large predators to avoid eating the toads. Big animals are more likely to grab big toads, which contain the most poison and can cause an instant heart attack. In a recent experiment the researchers laced cane toad meat with a drug that induces severe nausea and fed it northern quolls, cat-size marsupials that sometimes feed on the toads. The tainted meat doesn't kill the quolls, but it makes them very ill. In the field "the ones that have been educated survive very well, the ones that haven't been educated die almost immediately," Shine says. The researchers have seen quoll populations bounce back in some study areas as a result of the training. Shine and his colleagues say the strategy may work for other large predators such as monitor lizards as well.