The death leaves just 74 whales in the pod that has failed to reproduce successfully in the past three years in waters off Washington state and Canada. The whales have been struggling with a dearth of their preferred prey, salmon, as well as pollution and boat noise.
The young Southern Resident orca that teams of experts have spent weeks trying to keep from dying hasn't been seen in days and could be dead.
Teams are searching for an ailing, critically endangered orca that a scientist who tracks the whale population in the Pacific Northwest says is likely dead.
Ken Balcomb of the Center for Whale Research said Thursday he believes the whale known as J50 "is gone". The NOAA said it is prepared to rescue J50 if she is separated from her pod or stranded. "We haven't given up hope". Authorities also alerted a network of people who respond when marine mammals wash ashore.
"It was striking to me how thin she was. she is the thinnest killer whale I've ever seen", said Gaydos.
The distinctive black-and-white orcas, known as southern resident killer whales, have struggled since they were listed as an endangered species in the USA and Canada well over a decade ago.
Whale experts feared the orca was dead earlier this month when J50 lagged behind her family and went missing.
The message, the Center for Whale Research said in a website post, is that extinction is looming "while the humans convene task forces and conference calls that result in nothing, or worse than nothing, diverting attention and resources from solving the underlying ecological problems".
The latest aerial images of J50 show a "peanut head" appearance, which is caused by loss of fat behind the head. J50 has been in poor condition for months and there were concerns over the Labour Day long weekend when she was not seen with the rest of her pod in the waters between Victoria and Seattle.