Biologists have managed to deliver what they believe is a full dose of antibiotics to an emaciated killer whale in the waters off British Columbia.

Michael Millstein with the National Oceanic and Atmospheric Administration in Portland, Ore., says the female, southern resident killer whale was spotted Monday and researchers were able to deliver a dart filled with the potentially life-saving medication.

He says the young orca, known as J50, is staying close to her mother and is active as the pod of whales moves toward the mouth of the Fraser River where they are expected to continue foraging for salmon.

Concern about J50 rose over the long weekend when the nearly four-year-old whale was not seen with the rest of her pod as it was spotted in waters between Victoria and Seattle.

J50 has been in poor condition for months and her death would further devastate the dwindling southern resident population where only 75 orcas remain, but Millstein says J50 is hanging on.

Experts are tracking J50 with the hope of administering a deworming medication and Millstein says another attempt could be made today.