The snail that stands like a dam

Grand Canyon restoration hinges on the recovery of a tiny, talented mollusk

  • The endangered Kanab ambersnail - Roy Averil

    urray/Ariz. Game and Fish Dept.
  • Vasey's Paradise

    Guy Webster photo

GRAND CANYON NATIONAL PARK, Ariz. - "Here's one!" The shout comes from Melinda Thompson, a research volunteer from Provo, Utah, as she crouches to watch a half-inch snail sliming across a rock ledge near a clump of red monkeyflowers. "I think it's an ambersnail!"

Thompson and a group of scientists have just climbed about 45 minutes up Elves Chasm, a canyon that rises out of the Grand Canyon. It's day eight of a 15-day research trip down the Colorado River.

Jeff Sorensen, an Arizona Game and Fish Department biologist leading the expedition, hurries over.

"It is," he says. "Wow, they're moving out of the release area. They're venturing out."

That's good news for Grand Canyon boaters and for endangered fish, just a few of those who could benefit from man-made floods from Glen Canyon Dam like the one that restored some beaches and backwaters in 1996 (HCN, 7/22/96: Glen Canyon: Using a dam to heal a river).

The floods followed years of work by scientists to convince the Bureau of Reclamation to use the dam to restore the river, rather than just generate electricity and store water. But now those floods are on hold, as the tiny Kanab ambersnail, an endangered subspecies, is forcing managers to make tough decisions about the big dam and the river that runs through it.

Life in a turbulent world

The Kanab ambersnail is an air-breathing land snail that lives amid damp plant litter, eating leaves and stems, and being eaten by birds and rodents. Each snail develops both male and female sexual organs. Snails kept in isolation fertilize themselves. In groups, they seem to prefer fertilizing each other.

Some scientists surmise that the ability to breed without a mate is an adaptation to the snail's rough and tumble environment. Floods can leave snails stranded and wash them downstream. Those snails might then start subpopulations of their own.

But the flooding of Glen Canyon under Lake Powell may have erased some of the snail's upstream habitat for good. No one checked that area for Kanab ambersnails before it was inundated, but some scientists guess that a population in Glen Canyon may have periodically reseeded populations in the Grand Canyon.

Today, there are only two known natural populations of the snails. One is on private land near Kanab, Utah. The other is at Vasey's Paradise, about 100 yards from the Colorado River in the northeastern neck of Grand Canyon National Park.

Although the snails in Utah are protected under the Endangered Species Act, they are at risk because the owner plans to develop the land, says U.S. Fish and Wildlife Service biologist Debra Bills. The protection strategy she helped design focuses on the snails inside the national park, where the government has more control.

"We know Vasey's is not going to have a housing development put on it," Bills says.

But in 1996, when the Bureau of Reclamation opened the floodgates at Glen Canyon Dam, much of Vasey's Paradise was under several feet of muddy water. The floods washed out 16 percent of the snail's habitat. While the Bureau moved more than 1,000 snails to higher ground before the flood, hundreds died.

Now, a formal biological opinion from the U.S. Fish and Wildlife Service prohibits any large water releases from Glen Canyon Dam until an additional population of Kanab ambersnails is established.

An experiment on hold

All this presents an interesting conundrum for biologists working to restore the Colorado River. The dam has virtually eliminated spring floods that traditionally replenished beaches and backwaters. It has also turned the warm, muddy river into a cold, clear one. This has benefited some plants and animals, but is has been bruising to endangered fish such as the humpback chub.

The 1996 flood was an attempt to give native fish a boost and restore sandbars used by wildlife and boaters. Now, says Larry Stevens, a biologist for the Grand Canyon Wildlife Council and a member of the multi-agency Kanab Ambersnail Working Group, "the snails are seen as an impediment to the fish habitat."

Stevens argues that floods may actually benefit the snails. Insulating them from the selection pressure of floods may turn them into something different and more domesticated, he says.

Others are more cautious. Dave Wegner led planning and evaluation of the 1996 flood for the Bureau of Reclamation's Glen Canyon Environmental Studies program. It took him years of pushing Reclamation's hydropower bureaucracy to win permission for the release. Wegner, who now runs a consulting firm in Durango, Colo., supports the current restriction on experimental floods.

We can't protect an ecosystem without paying attention to the needs of individual species within it, he says. "That little snail has made us better scientists."

In the meantime, hopes rest on three snail populations that have been moved to places such as Elves Chasm, out of the reach of floods. The 300 transplants at Elves Chasm appear to be doing better than the ones at the other two sites. This spring's checkup found lots of snails and some egg masses, as well as the first snails venturing out of the release area.

But it is unclear when the translocated populations can be considered "established," to meet Fish and Wildlife's precondition for another flood. Fish and Wildlife's Bills has suggested that three years of a self-sustaining, reproducing population may be sufficient to justify calling it established. Other scientists have suggested waiting 10 to 30 years to judge.

Formerly a freelance writer in Arizona, the author now writes for the Jet Propulsion Laboratory in Pasadena, Calif.


  • Jeff Sorensen, Wildlife Specialist, Nongame and Endangered Wildlife Program, Arizona Game and Fish Department, 2221 W. Greenway Road, Phoenix, AZ 85023 (602/789-3740), [email protected];
  • Debra Bills, Fish and Wildlife Biologist, U.S. Fish and Wildlife Service, 2321 W. Royal Palm Road, Suite 103, Phoenix, AZ 85021, 602/640-2722, ext. 239, [email protected]

Copyright © 2000 HCN and Guy Webster

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