But Baldwin found allies in Lake Mead staff and other members of the 100th Meridian Initiative, a publicly funded consortium of state and federal agencies dedicated to keeping the zebra mussel — and other aquatic invasives — on the far side of the 100th meridian, the historic border of the West. They surveyed recreational boaters, the most likely cross-continental mussel carrier, and mounted educational campaigns to keep infested boats out of Western waters.

Baldwin was soon volunteering 10 to 15 hours a week on zebra mussel prevention. He talked to groups of boaters, agency staffers, and others about effective boat cleaning and inspection. “The best way to get their attention is to get in their knickers,” he says. “Tell them how it’s going to cost them personally.” He learned to build zebra mussel samplers out of PVC pipe and lengths of nylon cord and installed them at six Lake Mead marinas. He checked them monthly for evidence and reported his results to a mussel data clearinghouse at Portland State University in Oregon.

Whenever he could, he talked to marina workers about zebra mussels, describing what to look for as they went about their business. “Wen just kept after us,” says Gail Kaiser, whose family runs the Las Vegas Boat Harbor.

But what is one person’s persistence, compared with the powers of zebra and quagga mussels?

 

Invasion biologists like to talk about “propagule pressure,” or the number of times an invasive species enters an unfamiliar environment. The more numerous the propagules, the more likely the species will take hold. The propagule pressure of zebra and quagga mussels on Lake Mead was, and is, formidable.

The lake hosts some 8 million visitors each year, and on a summer weekend, as many as 5,000 boats launch on Lake Mead and its neighboring reservoir, Lake Mohave. While a small survey of boaters at the lakes in 2002 suggested that little more than 1 percent come from mussel-infested states, any one of those boats could carry enough live mussels or mussel larvae — vanishingly small bits of life known as veligers — to seed a new population.

Spot inspections at Lake Mead since May 2004 caught at least nine boats infected with invasive mussels, almost certainly a small percentage of the contaminated boats that entered the park. Officials for various agencies have also nabbed mussels in transit in Washington, California and elsewhere, and assume that many more have slipped by unseen. In the West, mussel propagules are present, persistent and resistant to detection; to settle in, all they need is a bit of good fortune.

The quaggas also had the advantage of anonymity. Baldwin and the biologists he talked to expected zebra mussels, which are now established in the Mississippi River and range as far west as Kansas and Oklahoma, to lead any invasion of Lake Mead. While the scientists were aware of quagga mussels, the species has only a small outpost on the Mississippi. The closest substantial population is in Lake Michigan, some 1,000 miles away from Lake Mead. Baldwin, playing the odds, designed his samplers for the shallower waters preferred by zebra mussels.

In February of last year, Baldwin dragged a plankton net through the Las Vegas harbor and turned up a microscopic globe of jelly that looked worryingly like a zebra mussel larva. Before taxonomists decreed it was benign, Park Service divers inspected the cables and mooring blocks at the harbor. They found nothing.

On Jan. 6 of this year, Baldwin got the call he dreaded. Eric Virgin, Gail Kaiser’s son-in-law and a member of the Las Vegas harbor staff, had found something suspicious while repairing an underwater cable. “It just seemed wrong,” he says now.

Baldwin drove to the harbor, where the marina workers showed him one of the “Zap the Zebra” educational pamphlets they’d been handing out to visitors. Taped to it was the mussel Virgin had plucked off the steel cable.

Later that day, divers found more mussels in the harbor, and at the nearby Lake Mead Marina. Over the next week, they found mussels at other locations throughout Boulder Basin, the western lobe of Lake Mead. The Lake Mead fish hatchery, a Nevada Department of Wildlife operation that stocks the lake with trout, was quarantined on Jan. 11 after workers discovered quagga mussels on the edges of the boards damming the fishponds.

Robert McMahon, a mussel expert at the University of Texas-Arlington, soon confirmed that the invaders weren’t zebras, but quaggas. Size measurements suggested that the population was at least two years old, though some researchers speculate that the lake’s warmer waters could lead to fast growth; the timing of the invasion remains uncertain.

While the evidence of infestation proliferated, so did its implications. The Southern Nevada Water Authority found quaggas on the outside of one of its Lake Mead intakes, some 90 feet below the surface. On Jan. 17, downstream from Lake Mohave in Lake Havasu, divers for the Metropolitan Water District of southern California found mussels attached to the outside of an intake for the Colorado River Aqueduct, the pipeline that waters Los Angeles. The following week, divers found mussels at the Central Arizona Project intakes in Lake Havasu. Later surveys turned up about a dozen mussels on an intake structure for Davis Dam, the plug for Lake Mohave, and another handful on the spillway gates for Parker Dam below Havasu. And in mid-February, an estimated 2,000 mussels were found on a “trash rack” protecting one of the intakes for Hoover Dam.

Park Service divers, more accustomed to pulling drowning victims out of the lakes than searching for mussels, spent most of January scouring lakes Mead and Mohave. During the weekend of January 20, they found more quaggas, this time stuck to docks and houseboats at the south end of Lake Mohave. Baldwin even discovered one of the lake’s largest quagga mussel specimens — the size of a hefty grape — stuck to the bottom of his own boat hoist. Lake Mead resource management chief Kent Turner says that given the number of mussel finds in Boulder Basin, and the density of mussels found at each location, it’s reasonable to assume that the quaggas in the reservoir already number in the millions.

At the Las Vegas Boat Harbor, more than three weeks after the initial discovery, Baldwin is still distressed. “I feel like I’ve been hit by a stick,” he says again.

He crosses the floating dock platforms, heading for the quiet boat slips on the northern edge of the marina. There, he unrolls his newest mussel sampler from a white plastic bucket. Redesigned to pick up quaggas, it extends his standard 6-foot samplers by 20 feet, and carries a doubled set of PVC tubing. He dunks its concrete anchor into the clear green water, and watches the nylon cord and its sampling tubes spin into the depths. Just a few feet away, gaggles of overfed carp, another import with a global reach, gather near the dock. Squirm-ing over one another to reach the surface, they push their mouths skyward, gaping for handouts.