J-50 was last seen Friday in Canadian waters, but she and the rest of the J-pod have not been seen since.
Michael Milstein, a spokesman with NOAA Fisheries, says researchers on Wednesday spotted the 20-year-old whale known as J35 carrying her dead young off the tip of Washington's Olympic Peninsula.
Scientists are still not sure why the whale has lost so much weight and believe an infection could be one of the problems.
"Even if her family is foraging for and sharing fish with her, J35 can not be getting the nutrition she needs to regain any body-mass loss that would have naturally occurred during the gestation of her foetus and also additional loss of nutrition during these weeks of mourning", she added.
J-50 is almost four years old and part of the critically endangered southern residents, a population of killer whales with only about 75 individuals.
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J-pod recently drew an worldwide spotlight when another orca, J35, was spotted pushing the body of her dead calf through the water for more than a week. As a young female, J50 holds particularly high value because of her future reproductive capacity. "It's fantastic. We're hoping she's going to be OK".
The race to save J50, a female with the potential to reproduce, is considered crucial for the endangered southern resident killer whale population that stands at just 75 whales.
The search is on again for J50, the ailing killer whale, in a cross-border effort to save her life.
The weather and the location of the orcas are complicating factors that could prevent intervention, said Paul Cottrell, a marine mammals co-ordinator with DFO. The pod has been keeping to the outer coast and west end of the Strait of Juan de Fuca and environs.
If J50 is in American waters and needs antibiotics, Rowles said the next step will be to administer an antibiotic that lasts 10 to 14 days.
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NOAA says it has legal authorization to try something it's never done before, which is feed the whale live medicated chinook salmon, as a way of delivering oral antibiotics.
"It was foggy up there for most of the day", Cottrell said.
Canadian officials have not received an application to administer antibiotics to the whale in Canadian waters, Cottell said, a procedure NOAA wants to try if J50 is in Washington waters.
Barre said multiple boat teams were on standby Monday to be in the position to collect breath droplets and feces from J50, which could provide better diagnostic information for why this orca is in markedly worse condition and malnourished compared to her relatives. She was the first orca to be rescued, rehabilitated and successfully released back into the wild.
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