Those focused on the Upper Basin, meanwhile, tend to dismiss the Lower Basin efforts as futile, given that nothing approaching ecosystem-scale recovery can ever take place in what is essentially a system of reservoirs. While some environmental groups have participated in the various Lower Basin conservation initiatives, none of them have given the razorback sustained support. "The river had been so transformed that it was a question of what could possibly be accomplished there," said Dan Luecke, a hydrologist and longtime participant in Upper Basin efforts, recalling a long-ago decision by the group Environmental Defense not to join an early Lower Basin recovery program.

But to the Lower Basin's champions, the fact that adult razorbacks survived for years in Mohave is proof that the efforts remain worthwhile -- even imperative. Just because there are dams on the river, they say, is no reason to give up on native species that evolved there. Tom Dowling, the geneticist, recalls a talk he gave at a fisheries conference several years ago, after which an audience member asked why Dowling was worried about biodiversity if the presence of non-natives meant there were now more species living in the river than ever before. "He asked, ‘Isn't that a good thing?' " Dowling said. "I was like, ‘You're missing the point completely!' As conservation biologists, it's important to understand what the different units are and try to preserve them. They co-evolved with the system."

Minckley, who died in 2001, laid out his own conservation plan for the razorback and other endangered fishes in the lower Colorado, in a scientific paper published posthumously and co-authored by Marsh, Dowling and others. He called for a more ambitious series of "protected, off-channel habitats," free of exotic species, where the razorbacks and other natives could breed and grow big enough to survive in the lake. The plan envisioned a series of "excavated habitats" resembling the river's original floodplain and constructed to keep non-native fish out. Hatchery-raised razorbacks would spend an additional year or two in these ponds before being netted and transferred into the lake (or elsewhere on the river). Though there has been wide support for the concept, it has yet to be implemented on a large scale. "The wheels turn slowly," said Marsh.

But even if Minckley's plan were carried out exactly as he envisioned, the razorback's survival would remain entirely dependent on sustained human intervention. That is not "recovery," nor is it the original intent of the Endangered Species Act. Yet it's a situation faced not just by razorback suckers but by most endangered species in the United States -- and likely around the world. There is no way they will survive without constant management. One recent study noted that "conservation-reliant" species now make up about 85 percent of those listed under the ESA.

So is it worth the effort? Does it make sense to set ourselves up as perpetual caretakers, indefinitely footing the bill and bearing ultimate responsibility for these creatures' presence or absence from the planet?

We work to save endangered species for many reasons. We do it for their genetic legacy, their place in the ecosystem, their commercial value, their moral right to exist. Sometimes it's simply for the love of a fascinating natural creation. Yet there is one overriding reason that binds us all, whatever our beliefs: Protecting endangered species is the law.

"There are some cases that seem perhaps less hopeful than others," said Sylvia M. Fallon, a wildlife conservation scientist with the Natural Resources Defense Council and an expert on the ESA. "But the law is designed to provide a legally enforceable way to make sure that we do what we can to identify threats and eliminate or mitigate those threats." Ultimately, said Fallon, the law is about "keeping all the pieces in place and not letting the whole web of life come apart."

But the pieces are countless, and budgets are finite. When it comes to some endangered species, law and economics may be on a collision course.

"I'm not sure I really truly believe in recovery for these fishes," Tom Burke told me one evening, as we sat on the upper deck of a houseboat the Bureau of Reclamation had rented for the Roundup. A waxing crescent moon glimmered just behind Burke's head, and the Big Dipper hung handle-side down, like a celestial question mark suspended over the lake.

It's not that Burke thinks razorback suckers on the lower Colorado should be abandoned to history. He's just a realist, looking out from the vantage of a long career. He's retiring in July, leaving Marsh and others worried about the fate of the program. "I believe we can do conservation, keep these species going for as long as we want to make a positive effort," he said. "But they have to be managed. I'm not saying these are zoo populations, but it's difficult for them to complete their life history without some outside help. And I don't see that ever changing."

Scientists who have spent their careers trying to save the native fish of the Colorado often wonder if their efforts will, ultimately, make any difference. "We're almost 30 years after the last amendments to the Endangered Species Act were passed in '73," said Marsh, "and no one would argue that native fishes of the Southwest are in better shape today than when the act was passed. We're actually losing ground." But he, for one, refuses to give up just yet. Politics might change, attitudes might change, some sort of breakthrough is always possible. "I guess I hope that if we knock on the door long enough that the door will open and things will move forward in a more meaningful way," he told me.

Before the crescent moon had risen that night, as the early spring sun fell toward Lake Mohave's Nevada coastline, Arizona's hills turned fiery pink. Bats shared the sky with seagulls and pelicans. A bald eagle, that ESA poster child, perched in a tree along what once was the edge of a canyon above a free-flowing Colorado River. As his staff worked nets for the second time that day, hoping to find more tagged razorbacks in order to unlock the mysteries of which fish were surviving, and why, Marsh looked out over the lake and tried to imagine its waters somehow cleansed of the species that don't belong here.

"It wouldn't be devoid of fish," he said. "The resources the natives need are all here. Fish are primitive and highly adaptive. So you give them a few elements -- water, food, shelter, real fundamental things -- they'll do OK."

Hillary Rosner has written about science and the environment for Mother Jones, The New York Times, Newsweek, OnEarth and many other publications.

This story was funded by a grant from the David and Lucile Packard Foundation.

For more information, visit:

The Lower Colorado River Multi-Species Conservation Program

The Upper Colorado River Endangered Fish Recovery Program

Marsh and Associates Native Fish Lab