SAN FRANCISCO - Scientists observing the wayward wanderings of two humpback whales in a California river have more to celebrate than their return to the Pacific Ocean - the duo provided an unexpected opportunity to study the endangered species.

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 spending more than two weeks trying to coax the whales back to sea with mixed results, officials were ready Wednesday to declare Operation Humpback a success. Since the previously conspicuous whales had not been seen for a full day, officials assumed the duo found their way home, undoing a wrong turn that inspired a range of rescue attempts.

The whales, believed to be a mother and calf, were last observed at sunset Tuesday swimming in San Francisco Bay about 10 miles north of the city. A convoy of boats that accompanied the whales across the bay to keep traffic at a distance stopped escorting them when it got dark.

Officials think the whales slipped out of San Francisco Bay to the open sea late Tuesday night or early Wednesday morning, when no one was watching.

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 relied on reports from commercial vessels and Coast Guard patrols to determine if the humpbacks still were in the bay.

Officials said they will never know why the humpbacks swam 90 miles inland.

But their journey marks 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. It also was the first time that whales swimming free in the wild were successfully treated with antibiotics.

The pair apparently were injured by a boat at some point, and officials said their wounds might have played a role in their becoming stranded in the fresh water of the Sacramento-San Joaquin River Delta. Based on the way their skin deteriorated while they were in the delta, marine scientists now have a clearer idea of how long whales can survive in fresh water, Gulland 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 them with fire hoses and banging metal pipes dangling beneath the water.

Those involved in the rescue effort said they did not know if the methods hastened the whales' exit or hindered it. They tried to strike a balance between getting the whales going and not making the problem worse.

“What we ultimately came away with is that many of the techniques had some effect, but none of them could make a whale go in a direction it did not want to go,” said John Calambokidis, a scientist with the nonprofit Cascadia Research Collective.

Officials speculated Wednesday that antibiotics given to the whales on Saturday to try to heal their wounds may have been a factor in their departure. The pair began their hasty retreat from the delta after receiving them.

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.

Gulland said she would not be ready to celebrate until Sunday, when she could be more certain the humpbacks were safely on their way.

Officials were unsure how much was spent on the rescue efforts, but they insisted the expenditures of time and money were justified, if not required under wildlife protection laws. They urged people who were captivated by the whales and followed their progress to transfer their energy to protecting marine habitats.