Biologists administered what they believe is a full dose of antibiotics to an emaciated killer whale in the waters off British Columbia on Tuesday.

Michael Millstein, who is with the National Oceanic and Atmospheric Administration in Portland, Ore., says the female southern resident killer whale known as J50 was spotted Monday and researchers were able to deliver a dart filled with the potentially lifesaving medication. Video of the manoeuvre was released later in the day.

"Martin Haulena, the veterinarian from Vancouver Aquarium who administered it, believes that most of the dose was delivered,"​ Millstein said in a telephone interview.

Millstein said team members were pleased with the outcome because the first time a dart was used to deliver medication to the animal, in early August, Haulena suspected it fell out before releasing a full dose.

The three-year-old orca is staying close to its 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.

"The teams did remark on just how emaciated J50 is," said Millstein after researchers located the young whale.

'She has some fight in her'

J50 has often lagged far behind other members of the pod as it travels through coastal waters from B.C. to California and back.

Concern that the young whale had died arose over the long weekend when it wasn't seen with the rest of its pod in the waters between Victoria and Seattle.

"They have never seen a whale this emaciated hang on for this long so she has some fight in her, it seems," Millstein said of the researchers who have been watching the whale.

Researchers have been able to deliver a second dose of antibiotics to the young orca J50, which scientists say appears emaciated. (Brian Gisborne/DFO)

J50 has been in poor condition for months and the killer whale's death would further devastate the dwindling southern resident population. Only 75 orcas remain.

In May, Environment Minister Catherine McKenna said the species faces imminent threats to survival and recovery and the government limited the Chinook fishery off the B.C. coast in an effort to increase the main food source for the whales.

Biologists were not able to administer a deworming medication to J50 on Monday, but Millstein expected further attempts would be made, depending on available boats, crews, water conditions and the location of the pod.

"There are indications that J50 may have some parasitic worms that are common among marine mammals and typically are not a problem, but in compromised animals they can be, so that is the next step," he said.

J50 is staying close to her mother, according to scientists. (Katy Foster/NOAA Fisheries)

Because the whales appear to be travelling north toward the Fraser River, Millstein said Fisheries and Oceans Canada would be the lead agency while the pod is in Canadian waters.

A range of options for treatment of J50 has been discussed, including the possibility that the orca could be captured and held for life-saving treatment before being released to rejoin its pod, but Millstein said the first choice is to cause as little disturbance as possible.

"There are many advantages to her being with the other whales and we know they share prey so that's something we certainly want to respect as long as she is still with them and active with the pod."

With files from CBC News

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