Sydney - There are Australians alive today who went on school trips to whaling stations and ate their packed lunches after watching humpbacks hacked apart.

Now, 30 years after Canberra ended commercial whaling, cetaceans have morphed into objects of reverence.

Tourists board boats to glimpse them. Music shops sell recordings of their babble. The government parries demands that its warships sail to the Southern Ocean to blow Japanese whalers out of the water.

No surprises, then, that Sydney residents anguished over this week's teary tableau of a lost and starving baby whale sucking the hull of a yacht in hopes of a milk feed.

The 5-metre baby humpback, for reasons unlikely to ever be known, lost contact with its mother on their passage down the east coast to feeding grounds in Antarctica.

The yacht it was nuzzling was towed out to sea, in the hope that the following 2-week-old whale might rejoin its mother or be adopted by another lactating female, but there was no enchanting reunion, no helpful surrogate, and the calf swam back to the boats it thought were its pod.

The clamour for authorities to do something got louder as the creature the media dubbed Colin got weaker. Then, the outcome marine biologists had expected all along: a decision to administer a lethal injection of anaesthetics.

"The whole issue has been quite harrowing, not only for our staff but for the community in general, where people have really been concerned about this whale," a clearly distressed National Parks and Wildlife Service spokesman John Dengate told reporters. "They've said to us, 'Can't you do this? Can't you do that?' We've tried really hard to follow every bit of advice that's come through."

There was even a standoff with animal lovers who had rigged up a makeshift feeding device with a plastic sack and a hose they said would keep the calf alive long enough for another attempt at finding its mother.

Hard science ran up against the soft-hearted who, perhaps deceived by Free Willy and other feel-good animal rescue films, thought there had to be a happier ending.

Ron Ling, head of the whale rescue group ORCCA, explained that the sucking sounds from the baby whale that the yachtsmen recorded on their boat were misleading. Whales can't move their lips like other animals can and suckling is not what happens when a mother feeds her calf, he said.

"She squirts the milk out, which goes into the whale's mouth, and it's sealed off by a specially designed tongue to stop the salt water from getting in," Ling said. "To replicate that would be very, very hard to do."

The sentimentalists received succor from politicians who promised to move heaven and earth to save the little whale.

"Our hearts are breaking with what's happening with baby Colin," New South Wales Premier Morris Iemma said. "It's looking bleak, but every effort is being made."

International experts were summoned, the military called in, and equipment readied.

Whale expert Nick Gales said it was all just a sad charade. The improvised feeding device would not work and the longer-term prognosis was irredeemably grim, he said.

"To hold it here and feed it ... and then somehow get it to Antarctica where it would learn to feed on krill is simply impossible," Gales said.

Marine biologist Rochelle Constantine from New Zealand's Auckland University urged people to let nature take its course and not intervene.

"I think it's important for people to realize that now you've got this increasing number of whales passing your coast, you're going to see more of this happening," she said. "You're going to see more dead whales washing up on your shores and distressed whales, and I think people need to understand that nature sometimes is like this."