The first orca calf born in the last two years to an endangered pod of killer whales is missing and presumed dead just weeks after its birth, experts said on Tuesday.

The mother of the late baby orca has been seen now for the third day in a row swimming in waters off Washington state without her calf by her side.

"For the first two years, a calf is glued to its mother's side. This calf hasn't been seen with its mother, and that's conclusive that it died," Howard Garrett, co-director of the Washington-based Orca Network, told Reuters.

There are only about 78 orcas left in the Puget Sound area in Washington, down from 98 in 1995 and over 200 decades ago. The unique population was listed as endangered in 2005, but the birth of L-120, the missing baby calf, back in early September gave conservationists hope that the whales were on their way to recovery.

Now, it seems all their hopes are dashed as the search continues for L-120. Experts had given the baby orca between a 50 and 65 percent chance of survival.

"We were being guardedly optimistic that a turning point had been reached, but that is not the case," Ken Balcomb of the Center for Whale Research told The Associated Press (AP).

The largest members of the dolphin family, orcas are highly social and intelligent marine mammals that communicate using whistles and pulsed calls and maintain group cohesion or "pods" through their lifetime, according to the NOAA. These black and white beauties are identified by slight variations in the shape of their dorsal fins, the AP notes, and a distinctive whitish-gray patch of pigment behind the dorsal fin, called a saddle patch.

Threats to the population include pollution and overfishing of their major food source, chinook salmon, near the San Juan Islands in the Salish Sea.