RIO VISTA – Scientists injected a stranded mother whale and her calf with antibiotics Saturday to ward off infection in deep wounds that have worsened from long exposure to fresh water.

Veterinarians on a boat shot custom-made syringes with eight-inch needles at the humpbacks in what wildlife officials said was the first time antibiotics have ever been administered to whales in the wild.

“We're very excited about the fact that we were actually able to make this happen,” Bernadette Fees, deputy director of the California Department of Fish and Game, said.

The lost humpbacks continued to circle in the Sacramento River about 70 miles from the Pacific Ocean, where they have lingered since leaving the Port of Sacramento last Sunday.

After more than two weeks in fresh water, the whales' once smooth, shiny skin has become dull and rough. Tissue around the gashes likely inflicted by a run-in with a boat was starting to die off, biologists said.

The mother has already received two injections, with an attempt to administer a third planned for Saturday night or Sunday, Fees said. The calf received one injection.

“These doses should be good at least through the week before they would consider administering any other medications,” Fees said. The medication was expected to start working immediately.

Biologists also used a funnel attached to a pole to try to collect exhaled breath from the whales' blowholes but were not successful, Fees said.

Rescuers otherwise planned to leave the whales alone for the Memorial Day weekend except to monitor their health and maintain a 500-yard barrier around the humpbacks to protect them from heavy holiday boat traffic.

The whales, nicknamed Delta and Dawn, appeared to respond to Friday's effort to push them downriver by spraying them with fire hoses. Scientists planned to use three to five fire boats shooting streams of water Tuesday to drive the whales at least 15 miles to Antioch, where saltier water could help their health improve.

Nearly a week of boat crews banging on metal pipes beneath the water and playing whale recordings have failed to stir the stranded pair ocean-ward.

The pair made an apparent wrong turn earlier this month and headed upstream until they reached the Port of Sacramento, where they could go no farther. They turned around on their own last Sunday, possibly startled by the rumble of a tugboat's engines, and swam some 20 miles downriver to the Rio Vista Bridge, where they have circled ever since.