Marine researchers working to save an ailing killer whale have released live salmon into waters in front of the free-swimming orca.
But they did not see the critically endangered whale, called J50, take any of the eight salmon dropped from a boat.
The feeding operation was part of an extraordinary response effort to save the malnourished orca.
Killer whale J50 and her mother, J16, swim off the west coast of Vancouver Island. J50 is the sick whale that a team of experts are hoping to save by giving her antibiotics or feeding her
A vet also injected J50 with medication using a dart on Thursday.
Researchers want to see whether they can dose a live salmon with medication and feed it to the whale, but they first need to test whether it will take the fish.
As of Tuesday, it appeared that the ailing orca hadn’t eaten any of the live chinook salmon released to her at sea.
NOAA Fisheries biologist Brad Hanson told reporters on Monday that they will wait for the pod of whales to return to the inland waters of Washington state to evaluate the next step.
The whales were last seen heading west towards more open waters.

For the feeding attempt on Sunday, members of the Lummi Nation, a Native American tribe, and others moved their boat about 100 metres in front of J50 and other whales
The fish-eating whales have struggled for years because of lack of Chinook salmon — their preferred food source — toxic contamination and disturbance from vessel noise.
They are down to just 75 animals, the lowest in more than three decades.
Hanson said he saw J50 ‘slogging along’ with her pod mates off Washington state’s San Juan Island, about 100 miles north of Seattle.
She appeared tired from swimming into the current and was even moving backwards as other whales sprinted by her.
Her body condition is quite poor, he said, and she does not look ‘very vibrant’.
Parts of her cranium have begun to show, indicating that she may be severely malnourished.
She is not socialising, such as splashing, but experts are not seeing other things worsening, Hanson added.
For the feeding attempt on Sunday, members of the Lummi Nation, a Native American tribe, and others moved their boat about 100 metres in front of J50 and other whales.
Keeping ahead of the pod in challenging currents, they scooped out salmon from a bag on the back of the boat and pushed it through a blue tube into the water.
‘Did she detect the fish? We don’t know,’ Hanson said, according to the Seattle Times.
Hanson called it successful even though they did not see J50 take fish.
He said some of the whales responded to a salmon but it was not clear whether it was a fish that came off the boat.

Keeping ahead of the pod in challenging currents, they scooped out salmon from a bag on the back of the boat and pushed it through a blue tube into the water

A string of heartbreaking events over the last few weeks has brought heightened attention to a struggling pod of orcas living in the waters off the Pacific Northwest. The grieving mother, known as Tahlequah, has been clinging to her baby’s body for two weeks (pictured on July 24)
‘This type of thing has never been tried before,’ he said.
J50 is a 3½-year-old member of the J Pod of the southern-resident clan of killer whales, the Times noted.
Another orca known as J35 is also a part of the same pod as J50.
J35 struck an emotional chord for many around the world when images showed the grieving whale carrying her dead calf for more than two weeks and swimming 1,000 miles, before finally letting go of her baby this week.
Scientists have indicated that they were concerned about the mother’s condition, but that they were not considering removing her calf.
‘It would be very challenging and perhaps not in the best interest of the animal to go in and remove the calf,’ Hanson explained. ‘I’m not even sure we would be successful.’