Keiko's monitoring team, which has tracked him since he was released from his pen in Iceland in July, has started to feed him herring to shape him up, authorities said.

Locals in western Norway have seen Keiko change from a joyful player when he made a surprise visit to the Skaalvik fjord a week ago to a loner shying away from the curious crowds who have rushed to watch the world-famous whale.

Just one week ago, Keiko even allowed children to ride on his back.

"There has been a lot of fuss," said Lars Olav Lilleboe, the local Halsa municipality's Keiko coordinator, who liaises between Keiko's monitors and Norwegian authorities. He said a ban to keep people away had helped calm Keiko.

Millions of dollars have been spent on preparing the 10-metre (30-foot) animal for life in the wild after the 1993 movie "Free Willy" prompted a campaign for his release, but Keiko still seems to prefer human company.

Lilleboe said Keiko's monitors had started feeding Keiko by boat early this week with his favourite dish - herring - to make sure he moved around in the narrow fjord.

"They are feeding him to make him exercise," Lilleboe told Reuters. "This morning, he seemed happy and satisfied."

Lilleboe said a blood test of Keiko had showed a high level of white blood cells, indicating that the killer whale was either stressed or had caught a respiratory infection.

Keiko showed up in western Norway after swimming some 1,400 km (870 miles) from Iceland. He was spotted in the fjord on Sunday by two 12-year-olds fishing in a small rowing boat.

Among world support for Keiko, French celebrity animal right activist Brigitte Bardot wrote an open letter to Norwegian Crown Princess Mette-Marit last week, begging her to help save Keiko.

Norway, with long whaling traditions, is the only nation in the world that hunts whales commercially, ignoring a global moratorium. However, it only hunts the minke whale.

And a Norwegian pro-whaling Norwegian parliamentarian, Steinar Bastesen of the Coastal Party, told daily Aftenposten this week that there was no hope for Keiko in the wild, urging the United States to bring him back to captivity.

Norwegian authorities in cooperation with Keiko's monitoring team are expected to decide this week whether to lure him back to deep waters or retire him in a peaceful fjord in western Norway.