Scientists with the National Oceanic and Atmospheric Administration (NOAA) say they are concerned that the ailing killer whale known as J50 has not been seen in several days.
The orcas have struggled with pollution, boat noise and, most severely, a lack of their preferred prey, chinook salmon, because of dams, habitat loss and overfishing.
The deep scratches along her back and dorsal fin not only earned her the nickname "Scarlet", but may also indicate that the young female orca, J50, came into the world through harrowing means: Pulled out of her mother by other whales using their mouths.
"We're watching a population marching toward extinction", Ken Balcomb of the Centre for Whale Research said on Thursday. Her family was seen Wednesday but J50 was not among them.
By Thursday evening, however, there were still no sightings of J50 and the Center for Whale Research listed her as "presumed dead".
"This is a sign from the whales that all is not going well out there for recovery of the southern residents", Balcomb told the Seattle Times on Thursday.
The distinctive black-and-white orcas, known as southern resident killer whales, have struggled since they were listed as an endangered species in the U.S. and Canada well over a decade ago.
Another whale in the same pod, known as J35, triggered worldwide sympathy this summer when she kept the body of her dead calf afloat in waters for more than two weeks.
Officials were searching for the almost four-year-old whale in the water yesterday.
He believes she died between last Friday and Monday.
J50 is seen in 2016 with its mother J16. Efforts to save the sick whale have not been successful. "Teams were on the water searching yesterday and are increasing a broad transboundary search today with our on-water partners and counterparts in Canada", NOAA Fisheries spokesperson Michael Milstein said.
Crews in a U.S. Coast Guard helicopter, 10 vessels, whale watch crews and other resources on both sides of the border were involved in the search.
Only 75 southern resident killer whales remain.
Though J50 has been declared dead, federal officials said the search will continue on Friday, TIME reported.
The National Oceanic and Atmospheric Administration in the US said teams on the water and pilots are looking for J50, who has not been seen in several days.