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. 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.
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.
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.
Mr 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”. She is not socialising, such as splashing, but experts are not seeing other things worsening, Mr 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.
Mr 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.
“This type of thing has never been tried before,” he said.