One of the oldest known killer whales in the West Coast's southern resident population is missing and presumed dead, according to researchers.

The whale identified as J-2 — and known more affectionately as Granny — hasn't been spotted since Oct. 12, Ken Balcomb of the Centre for Whale Research in Washington state, said in a statement issued earlier this week. That was when Balcomb last saw Granny leading her pod north through Haro Strait.

"Perhaps other dedicated whale-watchers have seen her since then, but by year's end she is officially missing from the SRKW population, and with regret we now consider her deceased."

The matriarch of J-pod was one of the first identified by researchers in the 1970s. Based on studies of her family group, it was estimated she was born as early as 1911 — making her up to 105 years old.

"She is one of only a few 'resident' whales for which we do not know the precise age, because she was born long before our study began," said Balcomb in the statement.

"In 1987, we estimated that she was at least 45 years old and was more likely to have been 76 years old," he said.

The pod is the most studied population of killer whales in the world and the lifespan of a wild orca is generally 60 to 90 years.

Population in decline

The death is a blow to the endangered population of southern residents, which lost several members in 2016, after a baby boom of eight calves in 2015 pushed the population up to 85 whales.

"The population is now estimated to be 78 as of 31 December 2016, and J-pod contains only 24 individuals plus the wandering L-87," said Balcomb.

J-2, on the left, is with a large male in the waters between Point Roberts and Saturna Island. (Simon Pidcock/Ocean Ecoventures)

The other known deaths and disappearances in 2016 include:

While the individual causes of death vary, researchers blame the overall decline of the population on a shortage of their primary food — Chinook salmon — and high levels of toxins in the blubber, the result of pollutants in the water and food.

Balcomb said in years in which Chinook and other fish stocks are poor, the orcas are forced to metabolize their blubber, subsequently releasing toxins into their blood and organs.

Despite her age, Granny's death will be a blow to J-pod and the rest of the southern resident population, he said.

"She kept on going like the Energizer Bunny," said Balcomb. "Who will lead the pod into the future? Is there a future without food? What will the human leaders do?"