Whale researchers have confirmed that a newborn orca spotted last week near Vancouver Island is a girl, raising hopes for the endangered southern resident population.

The calf, which has been named J50, was first spotted on Dec. 30.

Ken Balcomb, a senior scientist at the Center for Whale Research on San Juan Island in Washington, says a couple of volunteers headed out to see how the whale pod was doing and captured some photos of the calf.

"[They] took photographs and confirmed that the baby was still there. And the baby actually rolled over and showed them the underside, and we confirmed it is a female, so that's wonderful news."

J50 rolled over and gave researchers a chance to see her belly and confirm it's a female. (Center for Whale Research)

The birth of a female is exciting news, because the population of southern resident killer whales is at historic lows. J50 brings the population to just 78.

"Girls are the ones that have babies and we're running real short on whales that are able to produce babies lately," said Balcomb.

Last month a pregnant female from the southern resident population was found dead off the east coast of Vancouver Island.

Balcomb says there is a high mortality rate for calves, but since it survived the first week, he's hopeful.

In the meantime, researchers still are trying to figure out the identity of J50's mother: J16, a 43-year-old mother of three surviving offspring, or her 16-year-old daughter, J36, who has yet to have a recorded calf.

"It quickly became the subject of mystery because it was swimming alongside a female whale that is estimated to be 43 years old – beyond the age calculated for reproductive senescence in these whales.

"Sometimes it takes a few encounters and some time to sort these things out because these whales are very caring for one another, and baby-sitting is not unusual, especially with grandmothers," said a statement released by the centre.