A helicopter later spotted the whales swimming near the harbour entrance, the mother with lacerations near her dorsal fin and the calf with an 80-centimetre gash.

“An alert had come out earlier on the radio so we knew the whales were in the vicinity and everyone was keeping a watch out,” said whale-watching tour operator Richard Ford.

“It just popped up in front of the ferry, there was nothing the ferry could do to avoid it.”  National Parks and Wildlife Service spokesman Geoff Ross said the whales appeared to be fine, although the propeller blade had sliced through the blubber layer and there was blood in the water.

“They do have amazing powers of recuperation so in all likelihood the animals will recover,” he told the Sidney Morning Herald. “The (calf) appears to be swimming well and swimming close to mum’s side so with a bit more love and some breastfeeding I think it’ll be fine.”