A humpback whale missing most of its tail has been spotted off Kaikoura.

It appeared the whale's tail flukes were missing but it was relaxed and moving well, Department of Conservation Kaikoura ranger Mike Morrissey said.

Mr Morrissey speculated the humpback's tail was torn off as a result of the whale getting badly entangled in rope.

He went out by boat to check on the whale on Monday and estimated the whale to be two to three years old.

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He noticed the wounds had healed which indicated it had lost the flukes some time ago.

"What was left of the whale's tail was tapered like an arrow tip. It's bewildering as to how it came to lose both its tail flukes. "Fortunately, the whale wasn't showing any signs of distress. It was swimming well and breaching, diving and rolling as humpback whales typically do," he said.

Department of Conservation advised boaties to take particular care not to disturb the whale and keep their distance from it to protect it. Boats must be kept at least 50 metres away from marine mammals, Mr Morrissey said.

The whale may move north from Kaikoura as humpback whales have started their annual migration to their South Pacific breeding grounds.

Anyone who spots the whale without tail flukes as it travels up the coast is asked to report it to Department of Conservation so its movements can be tracked on 0800 36 24 68.