Scientists working off the Yucatan Peninsula are preparing to use sound waves to search for information about an asteroid that may have wiped out the dinosaurs 65 million years ago.

　　But environmental activists are trying to shut the project down, saying the technology could harm whales, sea turtles and several varieties of fish that provide a livelihood for thousands of Mexicans along the gulf coast.

　　Marine seismologists from the University of Texas Institute of Geophysics, the Geophysics Institute at Mexico's Autonomous National University and Cambridge and London universities will use underwater seismic pulses to learn more about the Chicxulub (pronounced Sheek-shoo-LOOB) Crater, a depression measuring about 120 miles in diameter and centered just outside the port of Progreso, 190 miles west of Cancun.

　　The same technique is routinely used by scientific research vessels around the world to study earthquake faults, tsunami dangers and climate change, scientists say. It is used in Mexico by the state oil monopoly, Pemex, to search for new energy reserves.

　　But Rosario Sosa, president of the Yucatan-based civilian Association for the Rights of Animals and their Habitat, said the sound waves "damage the brain, or damage the cochlea of the ear, and disorient the animals so that they beach themselves or crash into boats."

　　"They are no longer capable of looking for food using their sonar," she said.

　　Scientists acknowledge there's evidence that points to Navy sonar causing whales to beach themselves. But they say there's no proof that seismic pulses have harmed marine animals, though much more research is needed to draw firm conclusions.

　　Thus far "there has not been any significant evidence that there is any harm being done to the marine animal population," said Maya Tolstoy, a research scientist with Columbia University's Lamont-Doherty Earth Observatory.

　　The observatory is in charge of operating the Maurice Ewing, the research vessel from which the scientists will work, about 50 miles offshore. The boat is owned by the U.S. National Science Foundation.

　　Located half-onshore and half-offshore, the Chicxulub Crater is believed to have been carved by a comet or asteroid 65 million years ago, and occurred simultaneously with the mass extinction of species, including the dinosaur.

　　It is the largest and best-preserved "impact" crater on Earth, said Gail Christeson, a University of Texas marine seismologist involved in the project.

　　Researchers will send sound waves into the seabed via compressed-air guns to try to create the three-dimensional structure of the crater and learn the speed of the asteroid or comet, the angle at which it hit the Earth, and its effects on the environment.

　　The information could lead to knowledge of how to respond to possible future asteroid hits, Christeson said. She said the research also will help scientists to better understand the aquifer system of the Yucatan because the crater controls the water supply.

　　But Sosa says that after the Maurice Ewing conducted research in the waters between the Baja California peninsula and mainland Mexico in October 2002, two beached whales were found in the area with evidence of damage to their ears.

　　She also says activists have come across dead dolphins and turtles in the gulf coast state of Campeche, where Pemex uses seismic pulses to explore for oil. An additional concern is that the sound waves could threaten fish stocks — the livelihood of about 30,000 families along the Gulf coast.

　　Christeson says she has participated in at least four seismic cruises, "and we have never seen any effect on marine life."

　　"It has been observed that the Navy sonar may have contributed to strandings of marine mammals," said Christeson. "Our sounds source is different from navy sonar. The amplitude is less and we also fire intermittently, so we will put a short burst of sound in water every 20 seconds. The Navy sweeps through different frequencies."

　　Mexico's national Environment Department granted the Maurice Ewing permission to operate after the scientists agreed to take along independent specialists to monitor sea animals; allow flight and underwater acoustic monitoring; work only during the day when it is easier to notice the animals; and maintain a 3,800-yard safety radius around the ship. The government will conduct its own monitoring flights as well, officials said.