slipped back into the Pacific Ocean after a two-week sojourn that took them 90 miles inland up the Sacramento River, scientists said Wednesday.
This may mark the end of an 18-day circus that included everything from banging pipes to boat herding. California officials won't say how much the entire venture will cost taxpayers, reports CBS Correspondent Sandra Hughes.
Rescuers launched several boats Wednesday morning in an effort to find the mother humpback and her calf but hadn't found them, said Bernadette Fees, deputy director of the California Department of Fish and Game.
The whales were last seen Tuesday night in San Francisco Bay, where few obstacles were left on their route past Alcatraz to the ocean.
"The assumption is if we have not sighted the mother and calf by late afternoon that they have made their way out to the Pacific," Fees said.
Rescuers planned to rely on commercial vessels and Coast Guard patrols on regular duty to watch for any sign of the pair in the bay.
Biologists originally planned to attach a satellite tracking tag to the mother humpback, but gusty wind and malfunctioning equipment stymied the effort.
The whales was first spotted May 13 in the Sacramento River and got as far as the Port of Sacramento before finally turning around. Thousands of people have since lined Northern California waterfronts to see them.
Biologists also said the chance to closely observe the pair for so long was invaluable for science, using the urgent situation to their advantage, gathering whale data for study, reports Hughes.
Ariadne Green, 57, of Vallejo, Calif., caught a glimpse of the pair on Tuesday and earlier in the week at Rio Vista, where the whales had circled for several days near a bridge. She described the humpbacks' inland visit as a "profound spiritual experience" but was equally grateful for their departure.
"They need to go home now because their health is in jeopardy," Green said. "It's good to know they're on their way back."
Biologists said the saltier water where the mother humpback whale and her calf had been swimming since leaving the Rio Vista area helped reverse some of the health problems caused by long exposure to fresh water.
Recent photographs showed that serious wounds suffered by both whales appeared to be healing, said Rod McInnis, a spokesman for the National Oceanic and Atmospheric Administration. Antibiotics were injected into the whales on Saturday to try to slow the damage from the gashes, likely from a boat's keel. Lesions that had formed on the humpbacks' skin over the weekend also appeared to be sloughing off, Fees said.
"We would love to be able to see them one last time and say goodbye," said Fees. "But if they've made their way home, that's what counts."