Aboriginal "whale whisperers" and weeping protesters failed to save the stricken calf, with Australian rangers destroying the animal with a fatal dose of anaesthetic.
The humpback whale, nicknamed "Colin" but later found to be female, was discovered at the weekend attempting to suckle from a moored yacht at Sydney's Pittwater Bay after being abandoned by its mother off Australia's east coast.
After a six-day effort to lead the calf back to open sea and re-unite it with other migrating humpbacks, rangers and scientists decided that it would be more humane to destroy the whale.
A vet report and blood tests on Thursday revealed the two-tonne calf, believed to be only two to three weeks old, was in poor condition and probably had only hours to live. It was suffering from shark bite wounds and breathing difficulties.
"Everyone is very connected to this animal and it is a very emotional decision," state Parks Service chief Sally Barnes told Australian radio on Friday. "I've taken the decision that I don't want to prolong the agony of this animal," she said.
The whale's struggle to survive captivated Australians, who strongly oppose Japanese "scientific" whale killing and flock to sea on whale-sighting tours during the giant mammals' annual Antarctic migration and breeding season in Australian waters.
A handful of outraged animal rights protesters who staged an overnight vigil in Sydney said the calf's drawn-out death, over 10 minutes after anaesthetic was injected, had brought scenes akin to the yearly Japanese Southern Ocean slaughter to Australian doorsteps.
"It was absolutely disgusting. They have towed him behind the boat, scenes reminiscent of what we've seen the Japanese fishing trawlers do. He was clearly still alive, he was clearly moving, the line was thrashing," said boat captain Alexander Littingham, from Devine Marine Group.
Littingham and other activists tried to block the whale's destruction with a state Supreme Court legal injunction but were too slow to save the animal. Some watchers shouted "murderer" as vets and scientists prepared to move in, watched by police.
"I don't understand why they didn't let it die quietly. It was obviously distressed. I'm 41 years old and almost collapsed," onlooker Michael Brown told News Ltd.
SCIENTIFIC DEBATE
Scientists debated for almost a week over whether the whale could be saved, pointing out that migrating whale pods passing Sydney's beaches were unlikely to adopt a strange calf.
"It would face a higher predation pressure from sharks. There is absolutely no information to suggest another humpback whale female would be available or wanting to adopt it," Southern Cross University Whale Research Centre Director Peter Harrison said.
Other whale researchers accused rescuers of interfering in a natural process and said the calf's mother had probably abandoned it because it had some genetic abnormality.
"It does happen from time to time that calfs, especially those born so far south of the birthing grounds will not make it," Will Ford, a spokesman for the whale watching industry in Sydney, said on Thursday.
The saga spread around the world via the Internet, with chat rooms and forums abuzz with opinions on how the whale's fate should have been handled.
After destroying the whale, rangers dragged the carcass by boat to a nearby beach and covered it with a tarpaulin and a tent ahead of an autopsy at Sydney's Taronga Zoo to determine what may have caused the calf's mother to abandon it.
An Aboriginal "whale whisperer" was brought to the bay from South Australia to "talk" to the stricken calf, which responded by nudging its head momentarily clear of the water after being stroked on the back and sung ancient indigenous songs.
"He heard me singing and came over. I looked at him and he was full of life. He had a few scratches and cuts on him and I was a bit worried about his eyes. All he needed is a mother's milk," whisperer Bunna Lawrie told the Sydney Morning Herald, pleading with authorities for a change of heart.
On Monday a team of workers towed the private yacht out to sea to try to lure the calf into deeper water, hoping that it would find its mother or another passing whale pod, but it was spotted close to the beach at Pittwater again on Tuesday.