UPDATE: Researchers call display of grief 'unprecedented'

More than two weeks since her newborn calf died, the killer whale known to researchers as J-35 has been spotted again Wednesday still carrying the calf's body.

The calf was born July 24, but died shortly after and the mother has refused to let go.

In the days that followed, J-35 drew worldwide attention for what looks to human observers like an extraordinary display of grief.

She has been seen pushing the dead offspring along the water with her forehead, or grasping the calf's tail in her mouth — activities that experts say take huge amounts of energy for a swimming whale.

J-35 hadn't been seen since last week when her family group, known as J-pod, swam into the fog off Vancouver Island, B.C.

But Wednesday afternoon, Fisheries and Oceans Canada observers spotted her again, with the calf, and a struggling young whale named J-50 that biologists are trying to help.

Our marine mammal experts have sighted <a href="https://twitter.com/hashtag/KillerWhale?src=hash&ref_src=twsrc%5Etfw">#KillerWhale</a> J50 and her mother J16 in US waters. J35 is with this pod and is still carrying her calf. We are continuing to work with <a href="https://twitter.com/NOAAFish_WCRO?ref_src=twsrc%5Etfw">@NOAAFish_WCRO</a> and other partners to monitor the situation. <a href="https://t.co/QUxyv284GG">https://t.co/QUxyv284GG</a> <a href="https://t.co/fziQ0JCQc2">pic.twitter.com/fziQ0JCQc2</a> —@DFO_Pacific

The J-pod is part of the critically endangered southern resident population of killer whales, with only 75 individuals left.

The last successful birth in the population was three years ago.