Tales of heroism are emerging from the accounts of survivors of a boating accident that left four scientists dead and a fifth missing in Mexico's Sea of Cortez. The four survivors returned home late Thursday, exhausted and emotionally spent. Two of the survivors gave their first public accounts to news reporters, describing acts of heroism by the expedition leaders -- ecology professor Gary Polis, chair of the University of California, Davis, environmental science and policy department, and postgraduate researcher Michael Rose -- as well as Japanese scientist Shigeru Nakano. "We want everybody to know that Michael and Gary gave their lives in helping to save people who were involved in this accident," said survivor Gary Huxel, a postgraduate researcher. "Both of them wore themselves out. Gary's heart just gave out." The boat's nine occupants tried to cling to the upside-down vessel after it capsized in rough seas. Huxel said Rose struggled to keep three Japanese scientists with the boat. However, two perished -- renowned termite ecology expert Takuya Abe, 55, and ecologist Masahiko Higashi, 45. The third, Shigeru Nakano, 37, is presumed dead. "I think Michael was so distraught, feeling so responsible for the loss that it killed him," Huxel said. "It literally killed him." Becca Lewison, a 28-year-old UC Davis graduate student, said the boat was returning from an island four miles offshore when the weather turned bad. "The boat filled with water, and a large wave shorted out the engine. The boat capsized, pushed over by a wall of water. "After three or four hours, we decided to swim to a nearby island," she said. "We were found the next morning." Others said Lewison was among the expedition's heroes. UC Davis Chancellor Larry Vanderhoef said another survivor, undergraduate student Sarah Ratay, 20, credited Lewison with giving her the encouragement she needed to make it to land. The survivors met with the Japanese scientists' family and friends on Thursday in San Diego. Vanderhoef said Huxel told Nakano's relatives that the researcher had saved his life, pulling him back to the boat several times. Nine members of the ill-fated expedition flew from San Diego to Sacramento International Airport on a turbojet chartered by UC Davis. Earlier in the day they had driven from Baja California to the Mexican-U.S. border. At the border crossing, they were interviewed by U.S. Coast Guard officials about the accident. Huxel expressed sorrow that "we couldn't bring back" others on the ill-fated boat. He offered condolences to the friends and families of the researchers who died. He also thanked the many people who helped bring the survivors home and "everybody who kept us in their minds and prayers." As he spoke, Lewison sat at his left, tears streaming down her face. Other members of the expedition were on another boat that made it safely back to land. They initially were unalarmed when the second boat, led by Polis, failed to show up, said Neal Van Alfen, dean of the College of Agricultural and Environmental Sciences. "They had a lot of confidence in Dr. Polis," Van Alfen said. "He was familiar with the area. He had been there many times. No one was really concerned. They assumed he had gone into some cove on one of the islands to weather it out." The survivors took part in Thursday night's media availability with the understanding that their words would serve as their public comment on the tragedy. They have declined to do additional interviews.