From the Youtube video description
On July 8, 2012, a mother dolphin was spotted with her calf in Sanniang Bay of Qinzhou City in Southern China. The mother appeared to be helping her calf stay afloat. And when a tourist vessel got close enough to see the baby, they saw that it was dead.
It had a long cut across its belly, probably from a boat propeller. Tourist boats often go dolphin spotting in nearby waters.
The calf looked like it had been dead for several days.
[ Mr. Su, Fisherman]: “The little dolphin was dead for two or three days, but its mother still stayed with it and carried it day and night, which has touched all of us and the tourists. Just like human beings, dolphins also have feelings. A mother’s love is noble and moving.”
Similar behavior in mother dolphins has been documented by an Italian scientist since 2007.
After several encounters with dolphins mourning their dead or nearly dead, scientists are starting to think that not only do dolphins grieve, they are also aware of their own mortality.