Rare penguin nursed back to health after mysterious, savage attacks on the species.

Conservationists say they'll probably never know what caused barracuda to maul dozens of endangered yellow-eyed penguins this year.

After finding savaged birds up and down the Otago coast each week over recent months, they were happy to last night celebrate the release of a penguin back to its habitat after a brief convalescence in the north.

Fittingly, that habitat was Victory Beach, on the Otago Peninsula - a spot the unsexed bird was also named after by veterinarians.

Dr Brett Gartrell, director of the Wildbase Hospital at Massey University, where Victory recovered, said around 40 injured adult yellow-eyeds had been rescued and taken to clinics around the country since summer.

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That amount was especially worrying given many of the penguins were from a local population of just a few hundred, which is itself a large chunk of the rare species' total numbers, between 6000 and 7000.

The nature of the lacerations - Victory suffered a nasty gash to the bone stretching from foot to leg - suggested barracuda were to blame.

"Penguin skin is quite tough and the only thing the guys down south think could do this is the really sharp teeth of the barracuda," Dr Gartrell said.

"Normally, it would only be one or two birds a year that are coming in, so why it's suddenly extended into this huge thing is just something we don't understand."

Yellow-Eyed Penguin Trust ranger Leith Thompson suggested water temperatures could have brought more barracuda to the area.

"There is talk about them maybe going after the same food source, and the barracuda accidentally snapping at the birds rather than attacking them," he said.

The trust was relieved the spate of attacks was now over, and that birds like Victory, who made the trip home on board an Air New Zealand flight yesterday, could return to the water.

Mr Thompson was chuffed to weigh in Victory at 6.3kg - most adults of the species weigh around 5kg - before the bird waddled on to a sand dune and happily dived into the freezing surf as night fell.

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"It's always good to get these little guys away," said Dr Gartrell, whose team has suffered its own bites - from the penguins. "It'll give our bruises a chance to heal."