At an estimated age of 105 years old, the orca known to researchers as "Granny" is presumed to be dead.

Labelled J2, she was a member of the Puget Sound orcas which are located in Washington State in the U.S., a small and closely monitored group of the species.

Over the last 40 years, J2 has been witnessed "thousands of times" according to the Center for Whale Research, but hasn't been seen since October.

She's believed to be the oldest of her species, give or take a 12-year margin of error.

She was last spotted swimming north on Haro Strait, well ahead of J pod -- one of the three family groups of whales that travel with their mothers or grandmothers.

"Perhaps other dedicated whale-watchers have seen her since then, but by year's end she is officially missing from the SRKW (Southern Resident Killer Whales) population, and with regret we now consider her deceased," the Center for Whale Research​'s Executive Director, Kenneth Balcomb, wrote in a touching obituary for J2.

The death brings the toll of dead or missing whales to seven in 2016, with the region's population of the whales down to 78 by the end of the year. That's despite the birth of eight babies in 2015.

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Listed as endangered in 2005, orcas continue to battle despite a decade of research, protection and recovery efforts -- struggling due to a lack of food, pollution and disturbances from marine vessels.

Decades ago there were more than 140 Southern Resident Killer Whales, declining to 71 in the 1970s when dozens were captured for display at marine parks and aquariums.

J2's long lifespan was an example of why orcas shouldn't be kept in captivity, but questions remain on who will lead J pod now, which contains 24 individuals.

Associated Presscontributed reporting.