San Francisco More than two weeks after they were first spotted far up the Sacramento River, two lost humpback whales appeared to have finally found their way home Wednesday.
Officials said they assumed the pair returned to the open sea, undoing a wrong turn that drew thousands of admirers and a flurry of rescue efforts.
The unpredictable duo, believed to be a mother and calf, were last seen at sunset Tuesday less than 10 miles from the Golden Gate Bridge, after they traveled 25 miles southwest from another busy bridge. The convoy of boats that accompanied them across the bay to keep traffic at a distance abandoned their escort service when it got dark.
Officials believe the whales slipped out of San Francisco Bay to the open sea late Tuesday or early Wednesday, when no one was watching.
"With no confirmed sighting in the bay, we feel confident that it is highly likely that the animals are outside the Golden Gate," said Scott Hill, a division manager for the National Oceanic & Atmospheric Administration.
To make sure the whales did not take another wrong turn, two government boats were launched Wednesday morning to look for them in the Pacific Ocean. Rescuers planned to rely on reports from commercial vessels and Coast Guard patrols to determine whether the humpbacks still were in the bay.
As the afternoon wore on, producing only a false sighting of two gray whales, officials grew increasingly confident that the humpbacks, which were injured by a boat during their two-week sojourn inland, were on the move and made plans to stop searching for them.
Marine scientists said Wednesday that although they will never know why the pair swam 90 miles inland, the intensive operation to rescue the humpbacks yielded valuable information about the endangered species. It was the first time the same humpbacks were studied in the wild for so long, according to Bernadette Fees, deputy director of the California Department of Fish and Game.
The information scientists gathered includes sound recordings, logs of their behavior and tissue samples from both the mother and calf, which will be analyzed to determine whether they come from a pod of whales that travel between Mexico and California.
"All those things are very hard to get. So what we are doing is filling up the knowledge bank on humpback whales in the wild," said Jim Oswald, a spokesman for the nonprofit Marine Mammal Center, a private scientific and rescue organization. The experience also could prove helpful in approaching other stranded whales, he said.
After the whales were spotted near Sacramento on May 13, officials spent days trying to goad them back to the ocean, playing recordings of other whales, surrounding them with boats, blasting the water near them with fire hoses and banging on metal pipes dangling beneath the water.
Those involved in the rescue effort said they did not know whether the various methods had hastened the whales' exit or hindered it. But they speculated Wednesday that antibiotics given to the whales on Saturday to try to slow the damage from their wounds may have marked a turning point, since the pair began their hasty retreat from the Sacramento-San Joaquin River Delta after that.
Biologists said the saltier water where the mother humpback whale and her calf had been swimming since leaving the delta helped reverse some of the health problems caused by long exposure to fresh water.