(CNN) -- U.S. and Mexican search teams scoured the Sea of Cortez for seven Americans still missing after a tourist boat capsized Sunday off the east coast of Mexico's Baja California peninsula and killed one American tourist.
Visibility was clear and the water was warm in the sea, also called the Gulf of California, but rescuers had not found any survivors since Monday, Coast Guard Lt. Bill Burwell told CNN.
However, he remained optimistic.
"If someone is out there, there is a good chance that they are still surviving, and we will keep looking for them," he said.
The boat was carrying more than 40 people when it capsized.
Harry Edwards, a spokesman for the U.S. State Department, said Tuesday that so far 19 American passengers have been rescued. But the search continues for seven more American passengers, he said.
U.S. authorities identified the killed American as Leslie Yee. Her city of residence was not immediately available, authorities said.
"The State Department expresses its condolences to the victim's family and remains in contact with the survivors and families of the missing," the agency said in a statement.
There were conflicting numbers on how many people were on the boat when it sank. Mexican authorities counted 43 passengers and crew, while the Coast Guard put the number at 44.
One of the surviving tourists is Charles Gibson, the chief of police services at Contra Costa Community College District in California. Gibson is an avid fisherman and has participated in the same deep sea fishing trip several times, said Contra Costa Community College spokesman Tim Leong.
Gibson's family has been in contact with him but Leong declined further comment about the circumstances of the incident pending Gibson's return from Mexico.
According to the Contra Costa Community College website, Gibson served in the U.S. Navy where he was assigned to the USS Ranger. He served two terms in Vietnam and received the Vietnam Service Medal.
Burwell said the Americans had a C-130 aircraft on scene helping with the search, and were plotting the drift from the site of the incident. Mexican authorities also had assets aiding in the search, he said.
The C-130 is equipped with survival gear, rafts and electronic sonar that can detect beacons and people in water, said Ron Clark, U.S. Auxiliary Flotilla Commander. The plane, which will cover a broad swath of the sea in the area, arrived after Coast Guard crews on Monday flew an H-60 Jayhawk helicopter over more than 42 miles of water. The C-130 can fly as low as 1,000 feet and is expected to search for five hours, Clark said.
The C-130 and the Mexican navy reported no sightings of the seven missing Americans as of Tuesday afternoon, said Petty Officer 2nd class Levi Read of the Coast Guard. The C-130 has been searching waters around the accident since 2 p.m. ET as Mexican authorities continued their search by helicopter, plane, boats and on-shore vehicles, said Read.
All 16 crew members of the Erik survived; another who had been on the list of crew members apparently failed to embark, a Mexican official said, citing passengers' accounts.
The Erik sank in the Sea of Cortez, near Isla San Luis, Mexico, east of Baja, at 2:30 a.m. Sunday, the Coast Guard said.
"They ran into some bad weather, capsized, the boat sank," said Petty Officer 2nd Class Henry Dunphy, a spokesman for the Coast Guard in San Diego. Several people swam to shore, walked to the nearest town and alerted the Mexican navy to what had happened, he added.
But the Mexican navy said it was alerted by the cook of the boat, who was rescued by fishermen along with two passengers. He told officials that 27 tourists had been aboard the Erik when it sank approximately 60 nautical miles south of San Felipe, the navy said in a news release.
All the rescued people were in good health and were taken to their hotels, with the exception of one person with diabetes who remained under observation, the navy said.
"We have been working with Mexican navy authorities and the U.S. Coast Guard in the search and rescue," Baja Sportfishing Inc. said in an e-mail. "Right now our main concern is making sure that everyone is accounted for."
The Erik was a 115-foot fishing boat with a 24-foot beam, according to the company's website. "Built in Holland, she was equipped with stabilizers to handle the turbulent North Sea," it said.
Later Monday, the website added, "Due to events occurring at this moment, all further trips are canceled."
Mike Flynn, an advertising representative who had booked the Erik for an excursion in October, said the boat specializes in fishing trips.
The boat serves as a "mother ship" that carries its passengers out to sea, where they then use smaller boats to fish for the day before returning, Flynn said. The Erik offered three meals a day, showers and other amenities for its guests, he said.
CNN's Tom Watkins, Helena DeMoura, Leslie Tripp, Stan Wilson, Sandra Endo and Michael Martinez contributed to this story.