Shifting a young orca from one side of Auckland to the other on a trailer was risking its life, an expert on marine mammals says.

Associate Professor Liz Slooten, an Otago University marine mammal biologist, said last night that although orca had a large home range - they had been known to move between Auckland and Kaikoura - the 4-year-old female rescued on Friday would be in danger if it remained on its own.

While she was unwilling to criticise the animal's relocation by trailer from Auckland's west coast to Takapuna Beach on the east, she questioned whether there were alternatives.

"It would have been a really tough call to know what to do. It might have been better to hold on to it in the Manukau Harbour [by keeping a boat with it] and see if the family came back or the weather improved so you could put it back out to sea on that side."

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