The start of spring quarter was marked by widespread mourning after at least three people died and two others were presumed dead during a research expedition in Mexico's Sea of Cortez. Among the presumed dead was department chair and world-renown spider and scorpion expert Gary Polis. Campus officials described the accident as one of the worst tragedies in UC Davis history. Polis was leading a 20-member team -- including graduate and undergraduate students and visiting Japanese scholars -- on a spring break research expedition to study spiders and scorpions on desert islands in Baja California when one of the team's boats capsized in rough seas. The dead were identified as postgraduate researcher and alumnus Mike Rose and Japanese scientists Takuya Abe and Masahiko Higashi of Kyoto University. Four people were rescued -- postgraduate researcher Gary Huxel, undergraduate student Sarah Ratay and graduate students Becca Lewison and Ralph Haygood. Campus officials worked on Wednesday to help bring them back to Davis. Some of the survivors told the Coast Guard they saw Polis die in the water after two hours of clinging to the overturned boat. The U.S. Coast Guard deployed a C130 plane Wednesday to search for the bodies of Polis and Shigeru Nakano of Kyoto University Colleagues said Polis had made several research expeditions to the region and knew his way around the islands well. "This is the kind of news that a chancellor worries about virtually every day," Chanc-ellor Larry Vanderhoef told a news conference Tuesday. "You always hope that it never will happen. But unfortunately, today it did." "My heart goes out to the families," Vanderhoef said. "This is a tragic, tragic event for them. We share their grief. This is one of the worst, if not the worst, days in the university's history. It's a very sad day." A campus memorial service is pending. About 20 people were participating in the weeklong expedition, said Lisa Lapin of the campus News Service. Of those, 11 had left campus for Mexico last Friday. Two 22-foot open, inflatable research boats left the town of Pueblo de Bahia de Los Angeles, about 300 nautical miles south of San Diego on Monday morning to conduct research on Isla de Cabeza de Caballo, located about 4 nautical miles off shore. Both boats headed back to port midday, but became separated when the wind whipped up 4- to 6-foot waves. When the crew of one boat arrived at port and realized the other vessel had not yet arrived, it returned to search for that boat. The boat was reported missing to officials in Mexico at 10:30 p.m. Monday night. Several survivors were discovered on the Isla de Los Gemelos Tuessday morning. They reported that their boat had begun to take on water and then flipped, leaving the occupants to swim for land. Neal Van Alfen, dean of the College of Agricultural and Environmental Sciences, was expected to fly to San Diego or Mexico on Wednesday to escort the survivors home. The survivors were taken to a small village north of Pueblo de Bahia de Los Angeles to be interviewed by investigators that same day. "The department is very somber today," Alan Hastings, professor and former chair of environmental science and policy said Tuesday. "It's a very, very close-knit department." Campus counselors met Wednesday afternoon with staff and faculty members to help them deal with their grief. Hastings said Polis was involved with Earthwatch Institute, a conservation organization that invited members of the public to pay to participate in research expeditions. As many as six people were on the trip through Earthwatch. The Japanese scholars were among Japan's leading ecologists. Hastings said the department had hoped the expedition would be the start of a more formal academic relationship with the Kyoto scientists. By Tuesday evening, the U.S. Coast Guard brought in an H-60 helicopter able to conduct night searches after receiving permission from the Mexican government to join in the search-and-rescue effort. Because the incident occurred in Mexico's territorial waters, the search-and-rescue effort was led by the Mexican Navy using a helicopter, fixed-wing aircraft and high-speed boats. The offices of U.S. Sen. Dianne Feinstein, D-San Francisco, and Rep. Doug Ose, R-West Sacramento, also worked with the U.S. Embassy in Mexico City to assist in the search efforts, and to assure the safe return of all those who took part in the expedition.