J Pod was seen off the south end of Vancouver Island by Canada's Fisheries and Oceans personnel late Tuesday.
The orca known as J50 appears emaciated and scientists have said she may have only days to live.
Scientists in Canada and the USA have been working together to save her life. "Where they are is not where these kind of activities could occur", said Paul Cottell, marine mammal coordinator for Fisheries Oceans Canada. But, obviously, her body condition has been waning in the last couple of weeks.
J50 and her brother in 2014. As a young female, experts say, she has reproductive potential and could play a vital role in the southern residents' recovery.
DFO research crews have been out on the water every day trying to locate J50. Researchers said Tuesday morning that such an extended absence is not uncommon for the pod. She was staying close to her mother and moving steadily. Then the whales disappeared back into the fog. This involves collecting breath and stool samples and observing her behaviour.
"We're going to make this happen, if it's deemed appropriate to do this", Cottrell said.
If a cause can be identified, the veterinarians on board will be able to sign off on the next step-the injection of a long-acting broad-spectrum antibiotic either from a pole or a dart gun.
The U.S. -based National Oceanic and Atmospheric Association (NOAA) has approval to attempt feeding the whale the medicated salmon but for now that could only take place in U.S. waters. If J50 responds to the salmon, they will be considered as a way to administer medications that may not be injectable.
Rowles said injections of antibiotics or sedatives have been given to other free-swimming whales or dolphins that were injured or entangled but it hasn't been done for free-swimming whales in this area.
Feeding J50 by bringing her live chinook salmon caught by the Lummi Nation could begin as soon as Thursday, depending on whether the health assessment is accomplished Wednesday, and its outcome.
Whale experts have been increasingly anxious about J50 after a researcher last month noticed an odour on the orca's breath, a smell detected on other orcas that later died.
Rowles said such imagery has shed more light on the whales' overall body condition and growth over time.
The orca, which was last seen Friday, is part of an endangered population that has dwindled to just 75 whales.
"Hopefully, they are doing well and foraging and doing what they need to do".
The young female orca has sparked an global rescue effort by Canadian and American scientists who have developed a novel plan to feed her salmon medicated with antibiotics.
Springer was two years old when she was found in Puget Sound near Seattle, ailing and separated from her pod.