Science / Medicine : Mexico Helps Rare Tortoise Bounce Back : Environment: The creature was nearly extinct. Now biologists from two nations are collaborating to reintroduce the species in Texas.

There was a time when herds of yellowish tortoises the size of laundry baskets grazed on cactus fruit and grass along the hot and thorny Rio Grande Valley.

Once as plentiful as jack rabbits (though not as fast), those lumbering Bolson tortoises were long ago hunted to extinction by early man throughout their range. In fact, Bolson tortoises were found only in fossil collections until a colony of 20 was discovered in the 1960s on a patch of desert about 150 miles south of here, near Durango, Mexico.

Mexican biologists, armed with environmental restrictions, wildlife husbandry techniques and the support of Coahuila Gov. Eliseo Mendoza Berrueto--who has come to be known as Mexico’s “Ecology Governor”--have raised the number of the endangered tortoises to about 5,000.

Now, in the first collaboration with a foreign government aimed at reviving a species in a U.S. national park, Mexican biologists hope to reintroduce some of the burgeoning colony of Bolson tortoises in this Texas region of rugged mountains and river canyons.

If it works, the tortoise would be just a beginning. Mexican biologists say other candidates for transplant to Big Bend include Mexican black bear, desert bighorn sheep and Mexican wolves.

In a reversal of traditional relations along the border, it is biologists in the United States who will be seeking scientific information from counterparts in Mexico if these plans are to succeed.

The reason: Most of the research on the Bolson tortoise and a variety of other rare animals such as Mexican black bear has been conducted in Mexico, where biologists have been studying them for years.

The question is whether federal officials working in vastly different political jurisdictions can overcome the historic mistrust that has stymied close cooperation in the past, wildlife experts in both the United States and Mexico said.

“There’s always been a certain amount of animosity across the Rio Grande because, in the past, it was ‘Big Brother gringo’ extending a hand to Mexico. It’s not that way anymore,” said Big Bend Chief Ranger Phil Koepp.

“In the old days, we were a federal enclave dictating to Mexicans how we were going to run things around here,” Koepp added. “Hell, they’ve been studying the Chihuahuan Desert a lot longer than we have.”

A key reason the Mexican government is eager to transplant some of the tortoises is that as a single colony they are vulnerable to a potentially catastrophic disease. Starting a colony in the tortoise’s ancestral haunts on Big Bend’s 800,000 acres of federally protected land would help ensure the survival of the species.

National Park Service officials are elated. Gopherus flavomarginatus --the largest of four tortoises found in North America, with a yellow-tinged shell reaching 16 inches across--has not roamed these parts in 10,000 years.

“We are hoping to bring in 200 to 250 tortoises from Mexico as early as spring,” Koepp said. “The public is going to love them.”

There is little doubt that the tortoise could survive in Big Bend--a region of towering coral cliffs, maroon hills and brushy desert valleys mirrored on the Mexican side of the chocolate-colored Rio Grande.

The Bolson tortoise is now restricted to a series of remote natural basins in the Chihuahuan Desert near the convergence of the Mexican states of Chihuahua, Coahuila and Durango. The basins are included in the Mapimi Biosphere Reserve, which is one of 250 conservation areas around the world designated by the United Nations Educational, Scientific and Cultural Organization.

Living in colonies, the tortoises spend as much as six months a year in subterranean burrows, where they take refuge from the sun’s killing heat until desert downpours cause seedlings to burst to life with the grass and flowers they feed on, said Bruce Bury, research zoologist with the U. S. Fish and Wildlife Service in Ft. Collins, Colo.

In Mexico, biologists have been “hatching tortoise eggs in captivity under controlled conditions to learn more about increasing the reproduction rate,” Bury said. At the same time, he said, adult tortoises have been outfitted with radio collars to study movement, habits and range.

Similar studies have been conducted on the rare Mexican black bear, about 900 of which live in Mexico’s nearby Sierra del Carmen Mountains, just south of the Rio Grande.

Black bear, which were common in Big Bend around the turn of the century, were hunted to extinction in the national park’s Chisos Range by 1945.

But on the Mexican side of the border, the bear population has proliferated under the protection of environmental laws. There are so many bears in Mexico that some have begun swimming across the river to the United States in search of new territory.

“We have been gathering information for years about the black bears in the Sierra del Carmens,” said Alphonso Ochoa, who works for Mexican Gov. Mendoza.

“We believe the bear will eventually repopulate the Chisos as they seek additional water and territory,” Ochoa said.

In fact, an unprecedented number of sightings reported this year by visitors to the park suggest that the bear may have already begun to push north across the river.

In 1989, there were 27 sightings of Mexican black bears in the park, compared with three in 1944. More important, park rangers in October recorded the first sighting of a breeding population of black bears--a sow with three cubs--in Big Bend in 45 years.

In July, two biologists from Mexico temporarily moved to Big Bend headquarters to help monitor the black bear and peregrine falcon populations along the international border.

But any proposal by the Park Service to protect or even study the bear, endangered peregrine falcon or any other species that crosses the borderline “requires the approval of Mexican officials,” said Big Bend’s Ramon Olivas, the only international cooperation specialist in a national park.

“There is growing mutual interest and respect for conserving natural resources on both sides of the border,” Olivas said. “As a result, there are many wonderful plans evolving out of closer ties with our friends across the Rio Grande.”

Said Ochoa: “There is only a river dividing us.”

Bolson Tortoise Gopherus flavomarginatus Extinct in Big Bend National Park for 10,000 years Largest terrestrial reptile in North America with shells reaching 16 inches across Live in colonies, spending as much as six months a year in underground burrows 200 to 250 of the endangered tortoises may be reintroduced to Big Bend this spring Mexican Black Bear Ursus americanus Hunted to extinction in Big Bend by 1945 About 900 live in Sierra del Carmen Mountains, southeast of the park 27 bear sightings in the park in 1989 Documented sighting of a breeding population within park in October--the first in over 45 years